Published Jointly by the United Nations Food and Agriculture Organization and the Peoples Republic of China
Alfalfa is the major forage crop produced in temperate regions of the world. In China, alfalfa has great potential for expansion, however domestic forage seed production is very limited. Over 90 percent of the alfalfa seed used in China must be imported, resulting in the use of un-adapted varieties, variable prices, and quality concerns. Presently, the demand for high quality seed of alfalfa and other forages is soaring in China to improve livestock production and for massive revegetation and construction projects. The Western Development Campaign will have a major impact on forage seed demands, and there are a number of seed production projects underway to increase the supply of domestic forage seeds.
Xinjiang shares many similarities with the western United States (USA) where alfalfa seed is produced. Both regions have good irrigated farmland, long and hot growing seasons, low humidity, and low precipitation in July and August. Several attempts have been made to develop a commercial alfalfa seed industry in Xinjiang, but these have had limited success. For example, widespread infestations of the parasitic weed dodder (Cuscuta spp.) in the Altai region have eliminated several seed bases.
Alfalfa seed produced in the western USA has become a major cash crop, and Xinjiang has the potential for similar development. Alfalfa seed production requires both science and “art”. In Xinjiang, production costs for alfalfa seed can exceed those of tomato or cotton, but profits on alfalfa seed could be much higher. As with all other high-value crops, there are a number of important cultural practices to optimise production. At first, many techniques appear to be too expensive or impractical. However, management decisions should be made based on net return after expenses, science, experience, etc. – not solely the cost of a new practice.
Alfalfa Seed Production
in the USA
Alfalfa forage is grown on about 13,000,000 hectares in the USA. Large concentrations of alfalfa are grown in the major dairy areas such as the upper Midwest, the Northeast, and the south-western USA. Alfalfa hay is also grown in the western and central regions for beef cattle, horses and other livestock. Alfalfa hay is a major cash crop in these regions.
The USA alfalfa seed production industry has advanced parallel with the increase in world alfalfa forage production. Through the 1950s, alfalfa seed was generally harvested from existing hay fields, and production levels were low (< 60 kg/ha). Later, alfalfa seed was grown commercially on broadcast-seeded land, and with improved pesticides, pollination and irrigation, yields through the 1960s were in the range of 200 to 800 kg/ha. In the 1970s, precision row crop techniques were adapted for alfalfa seed production. Growing alfalfa for seed in wide rows, plus other advances in pollination, insecticides, weed control by cultivation and herbicides, and improved irrigation management resulted in seed yields of over 800 kg/ha. Seed yields in recent years have averaged about 800 to 1,200 kg/ha, with occasional yields over 2,000 kg/ha. Presently, alfalfa seed is an important commercial crop in six western US states, with an annual value of over $US 80,000,000 in farmer receipts.
The alfalfa seed industry has grown dramatically in the last 50 years. Alfalfa seed production increased, and there were other significant changes since the 1970’s. University and federal research programmes developed disease and insect resistant varieties, improved production methods in irrigation and soil fertility, better pest management, and pollinators. Today, new US alfalfa varieties are developed almost exclusively (over 99 percent ) by private companies. Most of these companies are “vertically integrated” – they have in-house programmes for variety development, seed-stock (Breeder and Foundation seed) production, seed contracts with farmers, conditioning plants to clean and package seed, and employees or dealers for retail sales.
The demand for high-quality alfalfa seed has also resulted in the need for seed quality control and Certification standards. Many international, federal and state laws govern the standards for all seed to be marketed. In the USA, the Association of Official Seed Certifying Agencies is a national programme that oversees seed certification agencies in individual states. In order for alfalfa seed to be eligible for sale as Certified seed, there are several requirements for the production field and harvested seed. For example, in Montana, the field must not have been in alfalfa seed for a minimum of three years, and must be isolated from other alfalfa seed fields by a minimum of 15 metres. Certified seed can be harvested from a field for a maximum of six harvest years. The field must be inspected annually by a qualified inspector prior to harvest and all or a portion of a field may be rejected if isolation is inadequate, or if prohibited weeds are present. After harvest a sample is submitted for laboratory analysis for purity and germination. For both certified and all other seed sold, there are maximum tolerances for seeds of other crops or weeds present. In short, US seed certification standards have greatly improved alfalfa seed quality, and this has helped increase domestic and foreign markets.
Alfalfa Seed Production
There is tremendous potential for seed production of alfalfa and other forage crops in Xinjiang. Several varieties adapted to western China have been developed and tested throughout the region, and these are in high demand. These include ‘Xinmu No. 3’ which was developed by Xinjiang Agricultural University with FAO support for irrigated conditions in northern Xinjiang by , There is also the larger potential for Xinjiang to produce alfalfa seed of varieties for other provinces in China where seed production is not feasible due to the climate.
The purpose of this manual is to provide general guidelines for optimising alfalfa seed production. Most of these recommendations have been proven over a 50-year history in the USA, but may need to be modified for special situations in Xinjiang. Aside from the field, seed processing and laboratory techniques described, other factors will affect the success of a developing alfalfa seed industry such as quality regulations and market forces.
Alfalfa seed production has become a multi-million dollar industry in the USA since the 1970s. Science, “art” and good fortune were responsible for this: concentrated production in the semi-arid west to avoid rainfall and high humidity, high seed demand for increased dairy production and export markets, improved pesticides for control of harmful insects and weeds, better control of pollinators and introduction of the leaf-cutting bee, and better harvest methods such as the use of chemical desiccants. However, a major turning point came when alfalfa seed was grown in wide rows as “row crop” instead of in solid stands suitable for hay production. Many techniques and implements used for sugar beet, cotton, corn and other row crops were quickly adapted. As a result, seed yields in many areas now average from 800 to 1,200 kg/ha, occasionally as high as 2,000 kg/ha, so alfalfa seed is a valuable cash crop.
Alfalfa grown for seed is a different “crop” from alfalfa hay. Even though it is the same plant, some practices and growing conditions for high seed yield are quite different than those for high forage biomass.
Climate. Xinjiang shares several similarities to the western USA, relative to the eastern regions of these countries. Large quantities of alfalfa seed are used in the east, but seed production is best suited to the west. Alfalfa for seed requires long, hot summers with minimal summer rain to disrupt seed harvest. Low humidity is also beneficial to pollinator activity.
Site selection. Alfalfa grown for seed has some different requirements for growth conditions and culture than alfalfa forage. It is ideally produced on irrigated land in an arid environment. Select deep, well-drained soils where water supply can be controlled by irrigation. Sandy loam soils or other light soils are best. Water demands for alfalfa grown for seed are quite different from those for hay – good soil moisture is needed until bloom, then irrigation levels and timing are gradually cut back to mid-bloom; this causes the plant to have a more synchronous blooming at the expense of additional vegetative growth. The land should be fairly level to accommodate surface irrigation.
The soil should be deep, without a high water table or impermeable layer. For seed production, alfalfa has similar fertilizer needs and is limited to salt levels as for alfalfa forage. Alfalfa is a heavy user of P and K, and in some light soils responds to S and B applications. A thorough soil test is recommended prior to producing alfalfa on new soils, followed by adequate fertilization.
On newly-claimed land,
grow another crop such as wheat for at least two years before planting alfalfa.
For cropland, pay particular attention to the weed infestations and herbicides
used in the previous crops. Weed management is very critical in successful seed
production, and the very first step is prevention. Avoid weedy sites, particularly
if infested with troublesome broadleaf weeds such as dodder (Cuscuta), and clovers
(Trifolium spp. or Melilotus spp.). These species are difficult to control in
alfalfa, and very difficult to separate from alfalfa seed. A best decision on
these sites would be to grow a crop of wheat and manage the broadleaf weeds
thoroughly for a year before sowing alfalfa. Also, review herbicides applied
to a preceding crop – alfalfa is susceptible to some soil-active herbicides.
Field Preparation. Land preparation prior to sowing alfalfa or other row crops includes ploughing, followed by harrowing, possibly broadcasting fertilizer and herbicide application, disc harrowing, land levelling and rolling. For alfalfa and other small seeds, the soil should be fairly fine, free of large clods or residue and firm. For late-summer planting, the land is pre-irrigated prior to planting.
Growing Alfalfa as a Row
Advances in row crop production have been mostly due to a simple farm implement – the tool bar (may be two or more parallel bars). Toolbars are commonly used in Xinjiang for the cultivation of cotton, tomato, corn and sugar beet. Depending on tractor size and number of crop rows (2, 4, 6 or 8-row), toolbars range in width from 1 to 10 metres. The toolbar is attached to the three-point lift of a tractor, as opposed to a pull-type grain drill. For larger toolbars (> 4 rows, > 4 m), gauge wheels are attached to the ends of the bar. The three-point hitch and gauge wheels provide a “fixed” or rigid platform, which will pull consistently straight through the field, and at a consistent depth.
The concept of furrow-seedbed row crop farming with a toolbar is that all operations can be done precisely and repetitively with the same implement. Seed boxes can be mounted on the toolbar to accommodate sowing seed in wide rows. The seed boxes and various sizes of furrowers (“furrow bottoms” or “ditchers”) are attached at precise spacing along the toolbar. Later, sweeps, knives or other cultivation attachments are mounted on the toolbar. Due to the weight and time involved, most farmers have separate toolbars for planting and cultivation operations.
For example, a standard “4-row toolbar” used to prepare 4 seedbeds placed on 60 cm centres would have five furrow bottoms spaced 60 cm on the toolbar, and the toolbar would be at least three metres in length. Note that furrow width must accommodate the width of the tractor for later operations, so in this example the tractor width is 120 cm (centre-to-centre of the rear tires). To use the toolbar, the three-point hitch and gauge wheels are adjusted to be level, then the shanks that supports the furrow bottoms are set to the exact depth and angle to form the desired seedbeds.
Figure 1. Six-row toolbar used for furrowing and cultivating alfalfa in wide rows (photo from Certified Alfalfa Seed Council, USA).
Seed. Buy good quality seed of a known, marketable variety. In the USA, most alfalfa seed growers are under contract with a seed company, and they are provided with excellent-quality Foundation seed. In Xinjiang, Foundation seed of local varieties is sold by the Xinjiang Agricultural University, and in the near future Foundation seed may become available from other provinces or private seed companies. Be sure to read the seed tag which will specify purity and germination rate. High quality seed should have over 90 percent germination, but with limited ability to control drill rates, lower germination rates can be used. Do not use Foundation seed contaminated with dodder or other locally-prohibited weeds. You will infest your land, and increase your weed control costs.
Time of Seeding. Alfalfa is best planted in the early spring in late March or early April(same time as wheat or barley) or in the late summer. In Xinjiang, late summer, four to six weeks before the first frost, appears to be a promising time, because the long growing season may allow planting after an annual crop such as wheat. The alfalfa must be seeded so that it has emerged for at least six weeks prior to frost. This generally will require two or more irrigations to assure adequate growth to overwinter. An advantage of late summer seeding is that many summer annual weeds (next year’s weeds) will germinate then be killed in winter.
Sowing Optimal. alfalfa seed yields are grown on wide rows (>60 cm). Sprinkler irrigation systems are ideal for alfalfa establishment. For furrow irrigation, alfalfa can be planted on a seedbed with furrows between the alfalfa rows. Planting must occur on a firm, flat and uniform seedbed with the toolbar mounted with seed boxes. Note that a common grain drill may be used, however all subsequent furrowing or cultivation operations will never match the alfalfa rows exactly. After the land is prepared, pull furrows through the soil with a toolbar. If the seedbed is not firm, shape and compact it with packers attached to the toolbar.
The first pass with the toolbar should be as straight as possible. During the first pass the farmer should again check and adjust furrow depth and angle to the desired seedbed dimensions and shape. After the first pass through the field with the furrowers is completed, the toolbar is lifted and the tractor is turned around to make the second pass. Most large toolbars have a fold-down marker disc to provide a straight mark to follow on the second pass. For the second pass, the outside furrow bottom is placed in the outside furrow again, and four new furrows are created. In this manner, repeated sets of four new seedbeds are created in each pass. It is not critical that rows are exactly straight because all subsequent operations will occur on the same set of four seedbeds. In the US, most large six or eight-row toolbars have solid, V-shaped gauge wheels that track in the outside furrows – these in conjunction with the implement weight, and support on the tractor three-point hitch and outside gauge wheels provide for very straight tracking through the field.
There are numerous sizes, shapes and adjustments for the furrow bottoms to create any desired type of seedbed. For sowing alfalfa, often the furrow is shallow, and the seedbed is flat. Depending on soil conditions and available equipment, it may be necessary to shape or compact the seedbed. For alfalfa, bed shapers or packer wheels are often attached to the toolbar while furrowing to shape and pack the seedbed.
After pre-irrigation the planter units are placed exactly on the centres of each seedbed (at 60 cm in the example). For alfalfa, the seeder unit typically has double disc openers, followed by packer wheels. Each planter unit may have a small seed box, or a larger single box with multiple drop tubes. Again the toolbar is checked for level, and all planter units are set to be consistently at the proper depth.
Late summer sowings should be pre-irrigated. Pre-irrigation is necessary due to the deep moisture loss prior to and during tillage. Pre-irrigation will also insure that after planting, irrigation water can be applied to the new alfalfa field quickly, and emergence will be more uniform. Alfalfa growth is fast in late summer so long as adequate moisture is available. Again, allow for emergence at least six weeks before freezing temperatures.
For spring alfalfa sowing, all of the operations above should be done in the previous autumn to assure that sowing can occur as early as possible. If weeds are already present, they can be sprayed with non-selective herbicides without disturbing the seedbed.
Seed Rates. Alfalfa sown in wide rows for seed production can be seeded at low (<2 kg/ha) rates. In the USA, many producers can plant as low as 200 g/ha. Many local drills or seeders may not accurately plant these low rates. In these cases, the actual seeding rate can be reduced by diluting the seed with dead seed of alfalfa or another species of similar size (be sure to account for the germination rate of the Foundation seed). The seed should be inoculated immediately prior to planting with Rhizobium meliloti to insure proper nodulation. The alfalfa must be sown shallow (< 2 cm) in a firm seedbed. This is best done with a double disc opener with depth bands, followed by a packer wheel. Unless wind erosion is a serious problem, do not sow with a nurse crop.
Management During Emergence. Early spring sowings may receive adequate precipitation for establishment, however preparations should be made for immediate irrigation when needed. For late summer plantings, several applications of irrigation will be necessary, but likely no other care until the following spring. Normally, these plants will begin growth ahead of weeds, which is an advantage.
After establishment, weed control will be a major priority. With spring plantings it is typical that alfalfa and weeds emerge at the same time from spring precipitation. After emergence, cultivation is used to control weeds, and re-shape furrows and seedbeds for good irrigation. Note that this is the single largest advantage of precision planting with a toolbar. Since the alfalfa is grown in very consistent sets of four (or six or eight) rows, accurate cultivation can be rapid, and control about 80 percent of the weeds. This timeliness and accuracy reduces costs of herbicides, and allows the farmer to tend to other duties of irrigation, spraying, or work on other crops.
There are a wide variety of cultivator attachments, and farmers improvise many for their own needs. Weed control in the furrows is accomplished with sweeps, which run just below the soil surface to cut weed roots. Sweeps come in numerous sizes, and can be adjusted for depth and angle. The sweeps are mounted on shanks attached to the toolbar, again on precise 60-cm centres. For precision control adjacent to the alfalfa rows, cut-away discs or knives are used. These are in pairs, about eight centimetres in width, which run on either side of the alfalfa row. These provide accurate weed control up to the narrow band of alfalfa. Many cotton growers install “hoods” for the first cultivation to prevent seedlings from being buried by soil from the action of the sweeps. Hoods are then removed for subsequent cultivations. Other cultivator attachments include knives for deeper soil disturbance, or roller tines to break crust on the sides of the seedbed for aeration. Another common attachment used in some areas for early cultivation are “torpedoes” – these are just round cylinders fixed or dragged from the toolbar to pack the furrow for irrigation. These are useful for light-textured soils with very little slope to speed water movement. Again, there are countless attachments and configurations used on cultivator toolbars.
To use the cultivator, it is placed in the first set of four rows, matching the furrower and seeder. It is checked for level and placement of all attachments. Most farmers develop the “art” of cultivator adjustment, and it varies from field to field, and among operations in the same field. Cultivator adjustments are made, then the toolbar is pulled at the desired final speed. Often, cultivator action varies with speed, so adjustments made at too slow a speed will need to be corrected again.
After cultivation, aeration and plant growth improve, but this will require subsequent irrigation. Commonly, a new alfalfa stand is cultivated two or more times up to the point when bloom and pollination occur. Each successive cultivation may use different cultivator attachments and settings.
A toolbar-mounted sprayer is another innovation used in alfalfa seed production. A spray tank is attached to the tractor or towed on a trailer behind the toolbar. There are two opposite uses for toolbar sprayers – in the crop row or in the furrow. For the first, a selective herbicide (grass herbicide, 2,4 D-B, etc. safe to alfalfa) is applied in a narrow band on the crop row. The advantage of this is the 75 percent reduction in herbicide cost. For furrow applications, hoods are mounted on the toolbar to shield the alfalfa crop from herbicide (non-selective – glyphosate, gramoxone, etc.) being sprayed in a wide band over the furrow. This type of application is becoming more important in the US because these herbicides are inexpensive, and application can occur later than cultivation. Also, furrow spraying requires less fuel than cultivation, and is faster and less expensive than hand labour.
If frequent rains prevent cultivation, control weeds early with selective herbicides. Otherwise, cultivation can effectively control 80 percent of the weeds. Cultivation will dry the soil, so begin irrigation to maintain good soil moisture conditions. Spring management until bloom will consist of herbicide application, followed by several repeated rounds of cultivation, hand weeding and irrigation.
Complete weed control is desired, because uncontrolled weeds at this stage will mature with the alfalfa. Weed control is very critical – weeds use water, nutrients and light at the expense of the alfalfa crop. Several weeds are difficult to remove from alfalfa seed, resulting in the loss of good alfalfa and more cost in cleaning. Further, several weeds are more desired by pollinators, and some weeds are primary hosts for insect pests that will later move to the alfalfa. Weeds should also be controlled in ditches and the land adjacent to the alfalfa (see the weed management chapter).
During the pre-bloom period, it is critical to maintain a regular irrigation schedule to promote good vegetative growth. Do not allow the soil to become dry enough to stress the crop, because severe stress would occur before the entire field could be irrigated. At peak bloom, gradually decrease irrigation. Generally, high biomass production results in low seed yield. Tall (>1 metre) thick forage growth will produce less seed than shorter, vigorously blooming forage on the same soil. In some soils with a clay hardpan or a high water table, a common phenomenon is high seed production for one or two years, then in later years the alfalfa growth becomes more vegetative and tall with low seed yields, regardless of good irrigation management. (For more information refer to the irrigation chapter).
Figure 2. Furrow irrigation of alfalfa (photo from Certified Alfalfa Seed Council, USA).
Pest Control. Prior to bloom, monitor closely for insect pests such as weevil, aphids, lygus, grasshopper and cutworm. If these are building up prior to bloom, treat with an appropriate insecticide because during pollination, treatment is more limited.
Management During Bloom.
The final cultivation should occur prior to first bloom. Again, monitor insect populations and treat if necessary. At this time, irrigation timing and amount is gradually reduced. This will “stress” the alfalfa, resulting in more uniform blooming and better pollination. Depending on soil type and evapotranspiration, irrigation may be terminated when the alfalfa reaches full bloom, and green seed pods begin to form. At this time areas in the field known to be infested with dodder, and other difficult weeds should be spot-treated. In the USA, dodder patches (including the alfalfa and a perimeter of alfalfa) are treated with non-selective herbicide. This is the final opportunity to prevent wider infestation and seed production by dodder.
In the USA and Canada, most alfalfa seed growers provide additional pollinating bees to promote good pollination and seed yields. In fact, alfalfa seed is not a viable crop in most of the USA without additional pollinators. Improved pollination in these areas has been responsible for increasing seed yields by 25 to over 100 percent . In California, pollination is primarily done by honeybees (Apis mellifera ) by contract between a seed grower and a beekeeper. These are specialized colonies, cultured specifically for pollination of alfalfa, clover and orchard crops. Honeybee hives are placed in groups of 12 to 18 strong hives, about every 160 metres. The honeybee pollinates alfalfa accidentally, while probing for nectar. Alfalfa is not the most desirable nectar plant, and the honeybee is not the best pollinator. However, in California, attempts to use other pollinators have been unsuccessful.
The leaf-cutting bee (Megachile rotundata) is widely used in the north-western USA and Canada for alfalfa pollination. The leaf-cutting bee is native to many areas, and the females lay their eggs in small tunnels in trees or structures. In June the bees emerge, mate, and five days return to nesting sites to lay eggs. The females cut pieces of leaves to place in the nesting hole to protect each egg in an individual cell. The female supplies each cell with pollen and nectar, lays an egg, then repeats the process until the cell is full. Artificial cells are created by providing boards with holes, plastic or wood laminates with holes, etc. In artificial cells, about eight cells are made in each tunnel, and then it is capped with more leaf pieces. In some environments, the eggs will hatch in the same season, but in northern climates, there is only one generation, and the artificial habitat is put in cool storage for the winter. During the four to six-week life of one female leaf-cutting bee, she will pollinate enough flowers to create 100 g of seed, and she will produce about 12 healthy offspring (4 to 6 females).
In Canada and the northwest USA, the most successful alfalfa seed growers also have a viable leaf-cutting bee storage programme. During winter the leaf-cutting bee boards are disassembled and the loose cells of larvae are put in cold storage. One month prior to pollination, they are incubated on trays at about 29 degrees Celsius at 50 percent humidity. Male bees will emerge first and when this occurs, the bees are taken to the field site. Clean bee boards are then placed in shelters in the alfalfa field, facing the east. At least 10,000 female leaf-cutting bees are needed per hectare, but many growers now use over 20,000. Artificial culture of the leaf-cutting bee is critical for seed producers – if the bees are purchased, the pollination cost alone can be up to $US 600 per ha!
In Xinjiang alfalfa pollination may be very challenging. Near Hutubi alfalfa seed fields are grown in an area with a concentration of irrigated crops, open ditches and many trees. At this site, alfalfa is pollinated by large population of native bees, and seed yields of over 600 kg/ha are possible with no added bees. At other locations where there is a limited amount of irrigated cropland and few trees, potential seed productivity will be severely limited without supplemental bees. Several attempts to use leaf-cutting bees at Hutubi had limited success. Based on the consistent benefits to providing additional bees to alfalfa in the USA and Canada, it is likely that seed yields in Xinjiang will not reach their full potential until suitable pollinators are found and domesticated.
Prior to seed harvest the field should again be monitored for weeds, particularly the dodder patches that were treated. If a spot was missed, remove it by hand or by burning with a torch. The best method for alfalfa seed harvest is to spray with a desiccant (Diquat), when most of the pods are brown, followed by direct combining. Good coverage of the foliage by the desiccant is required, and seed can be harvested five seven days later. Consult the weather forecast because, after desiccation, an alfalfa seed crop is susceptible to significant seed loss from wind and small amounts of rainfall.
Once the crop has dried begin harvest in dry, warm conditions. Thoroughly clean the combine to remove contamination from seed of other alfalfa varieties, crops and weeds. The combine should be operated at low ground speed, with a low cylinder speed, and low air. After starting, repeatedly check the grain tank to assure that seed is not being damaged, and check the chaff row to look for high seed loss. Adjust the combine settings if necessary. Normal alfalfa seed should be plump and bright gold in colour. Be sure that all seed containers, wagons, conveyors and other equipment are clean and leak-proof. At this stage, the moisture content should permit safe indoor storage of seed in bins or bags until cleaning.
After harvest several autumn field treatments are necessary. All of the crop residue should be burned or removed. Do not feed chemically-desiccated material to livestock. Seed chalcids are very prevalent and if not controlled, can become very serious in alfalfa grown for seed. The only effective control measure is to bury the crop residue. Cultivation of the dry soil is an effective way to bury the remaining residue. Autumn cultivation, followed by irrigation is also an effective weed control method. Irrigate the alfalfa to go into the winter with a full profile. Ideally, any autumn regrowth of the alfalfa should not be cut or grazed. If the forage is utilized, it should be after the plants are completely dormant from cold temperatures to minimize winter injury.
Management of existing alfalfa seed fields
An alfalfa stand should be maintained for 30,000 to 50,000 plants per hectare for optimum seed production. Plant spacing within a row of about 15 cm is ideal. This can be accomplished in the autumn – after harvest, before cultivation – or in early spring. A toolbar cultivator with small sweeps mounted on spring shanks is more accurate than disc harrow.
After the first seed production year irrigation and fertility levels should be maintained for the duration of the stand. The importance of weed control remains critical in the alfalfa seed field for its life. Cultivation is the primary method of weed control. At this stage, several additional herbicide choices are available. Soil-active herbicides can be applied to dormant alfalfa, or alfalfa just starting to grow in spring, to control most germinating seeds. Of the soil active products, one (US trade name is Prowl) has excellent activity to control dodder. Glyphosate can be safely sprayed over the crop in the spring when it has very little new growth, to control winter annual weeds. Insect populations should continually be monitored, as these cycle from year to year.
A well-managed alfalfa seed field can remain in viable production for up to ten years. However, in the USA, the decision to terminate a field is primarily dictated by the three-year seed company contracts or by a stand limitation for variety Certification. Aside from these situations, seed yield yields generally decline, and weed invasions force the grower to terminate the field.
Crop Rotation. The alfalfa seed field can be killed with herbicides or ploughed. A field should then be planted to wheat or a grass crop to eliminate broadleaf weeds, for a minimum of two years before returning to alfalfa.
WEED MANAGEMENT IN ALFALFA
Jean Dawson, USDA-ARS Weed Scientist (retired), Prosser, Washington, USA
(With excerpts from Weed Management Handbook, Cooperative Extension Services
of Montana, Utah and Wyoming, USA)
Alfalfa seed is a very valuable crop. Weeds compete with alfalfa for light, water and nutrients, and can significantly reduce seed yields. During seed cleaning and conditioning, large amounts of valuable alfalfa seed can be lost when removing weed seeds. Several weeds such as dodder can never be removed to 100 percent , which may result in not being able to sell the alfalfa seed. Consequently, a major emphasis for producers is to grow alfalfa seed in fields as weed-free as possible. All management factors such as field selection, crop rotation, tillage, seed source, cultivation, irrigation, herbicides and harvest methods must be used together (integrated) to effectively control weeds.
Weed prevention is the exclusion of weed seed or vegetative propagules onto the land. This requires vigilance and the ability to identify weed seeds, seedlings, and mature plants. After a weed is introduced to a piece of land weed eradication is nearly impossible, and the endless process of weed control begins. Some suggestions:
• Avoid weed establishment;
eliminate individual survivors.
• Identify and map weed infestations.
• Keep records over years.
• Recognize and eliminate new weeds before they multiply and establish.
Employ sanitary procedures;
prevent weed spread.
• Clean equipment between sites or infestations.
• Examine nursery plants, seed, and imported soil or media. Use Certified Seed.
• Screen irrigation water that comes from surface storage through canals.
Control vegetation and seed sources around the field or site. Comply with or initiate national and local weed laws and noxious weed control programmes.
Weed Control by
Cultural weed control uses the principles of crop competition to exploit the crop’s abilities and the weed’s deficiencies. Alfalfa grown for forage reduces the ability of annual weeds to grow, but can favour growth of perennial weeds. In contrast, alfalfa grown for seed can have different weed control challenges from both annual and perennial weeds. Know the weed spectrum in a field then select the crops according to their ability to compete with those weeds. Rotate crops to disrupt weed life cycles or suppress weeds in a competitive crop before planting a less competitive crop.
Plant competitive crops instead of fallowing to improve soils and weed management:
• Consider specific
varieties of cereals with natural plant toxins (allelopathy); vegetation must
remain uniform on the soil surface; either perennial or large-seeded crops can
be planted through undisturbed mulch.
• Consider crops such as oats or spring barley that winter kill after vigorous autumn growth. This avoids or reduces the need for controls the following spring.
Alter planting dates to encourage maximum early crop growth or delay planting until the first flush of weeds is controlled.
Placement and time of application
of fertilizer, especially nitrogen.
• Band or spot fertilizer below crop seed to reduce its availability to surface-germinating weeds.
• Time the application of fertilizer using side-dressing for maximum crop growth or to minimize weeds.
Mechanical weed control involves the physical destruction of a weed. Techniques involve hand pulling or hoeing which are practical for small infestations. Mowing is often used but by far the commonest practice of mechanical control is tillage. Advantages of tillage include:
• Elimination of
• Controlling annual weeds
• Suppression of perennial weeds
• Tillage methods include ploughing, rototilling, disking, and harrowing. Cultivation implements for weed control include sweeps, rolling cultivators, finger weeders, push hoes, rotary hoes, etc.
Several excellent herbicide options are available for alfalfa seed production. Herbicides must be used properly and in conjunction with other cultural practices. Specific herbicides listed in this document are used in the U.S., and may not be available under the same trade names in Xinjiang.
Alfalfa weed control should be viewed as a three-phase programme. Each control phase represents a unique opportunity to address specific weed problems. Attention to all three phases is the key to successful weed management in alfalfa.
Phase 1: Pre-Crop
Perennial weeds are usually more difficult to manage in a perennial broadleaf crop. Therefore, every effort should be made to reduce or eliminate perennial weeds prior to planting alfalfa. Never plant a field to alfalfa before a perennial weed problem has been made manageable. Choose rotation crops preceding alfalfa which allow use of effective cultural and/or chemical weed control techniques. For example, small grains are compatible with numerous selective herbicides which are effective against perennial broadleaf weeds, but which are not tolerated by alfalfa (see small grains section). The non-selective herbicides Roundup or Landmaster can be very effective against both perennial grasses and broadleaf weeds when applied in the early autumn after harvest of any annual crop. Be mindful of time intervals required between the application of some herbicides and planting of alfalfa.
Phase 2: Seedling
Alfalfa seedlings freed from weed competition during their first few weeks of growth will produce higher-yielding and longer-lived stands. There is no more critical time to control weeds in alfalfa. Both pre-emergence and post-emergence herbicides exist which effectively eliminate weed competition without harming young alfalfa seedlings. Examples include Buctril, Butyrac, Eptam, Kerb, Poast, Pursuit, Select and Raptor. Clipping young stands of alfalfa also can reduce competition and shading from certain annual weeds.
All management practices during the first season should focus on optimising alfalfa establishment and survival. Select adapted varieties for your local growing conditions. Always plant weed-free seed of the highest possible quality. Use the ideal planting rate, seeding depth, fertilizer rate, and irrigation programme for your situation. The goal is to eliminate as much stress on young alfalfa seedlings as possible, so they can develop into a thick and vigorous stand of established alfalfa. Once established, a healthy, dense stand of alfalfa is very effective by itself in keeping out many weeds.
Planting small grains with alfalfa as a companion or nurse crop is discouraged, except in cases where severe soil crusting or wind erosion can make alfalfa establishment nearly impossible. Oats, barley, or wheat seedlings can compete with alfalfa for moisture, sunlight, and nutrients, much the same as grass weeds.
Herbicides in newly
Herbicides for early-emerging broadleaf weeds
2, 4-DB (Butyrac, Butoxone)
Herbicides for early-emerging grasses and volunteer wheat
Herbicides for early-emerging grasses and broadleaf weeds
Control of late-emerging grasses and broadleaf weeds
Phase 3: Established
Waiting until a stand is several years old and full of weeds is not the time to start a weed control programme in alfalfa. Weed control operations in this phase should be pre-emptive in nature, intended to preserve or improve the level of control achieved in phases 1 and 2. Begin well before a weed problem becomes serious. Any of several selective soil-residual herbicides can be applied in the late autumn or very early spring to dormant established alfalfa for control of annual grasses and/ or broadleaf weeds. Examples include Karmex, Kerb, Lexone, Prowl, Sencor, Treflan, Velpar and Zorial. Some can be helpful in managing certain perennial weeds.
Herbicide application accuracy and proper timing are always essential. Make sure spray equipment is correctly calibrated and maintained. Read and follow all label instructions.
Herbicides in established
Herbicides for winter annual and summer annual broadleaf weeds and grasses
Diuron (Karmex, Direx)
Herbicides for winter
annual broadleaf weeds and grasses
Trifluralin (Treflan TR-10, a granular formulation)
Herbicides for winter
annual broadleaf weeds and grasses
Herbicide for winter annual
MCPA (Several trade names)
Herbicides for perennial grasses
rows of alfalfa for seed production
Herbicides for annual broadleaf weeds and grasses.
Herbicides for annual
and perennial broadleaf weeds and grasses.
Herbicides for annual
and perennial broadleaf weeds
2, 4-D (Several trade names)
MCPA (Several trade names)
Herbicide applied before
preparing alfalfa seedbed
Practical programme to control weeds (other than dodder) in alfalfa
Alfalfa planted in the spring for hay or seed production
EPTC (Eptan) sprayed on
the soil and incorporated mechanically
2, 4-DB (Butyrac, Butoxone) applied post-emergence
Additional treatments for alfalfa grown in widely spaced rows for seed production
Hand burn to remove any
Trifluralin (Treflan) sprayed on soil and gently incorporated
Hand burn 1 or 2 times as needed
Glyphosate (Roundup) as directed spray between rows for field bindweed
Alfalfa planted in late summer for hay or seed production
EPTC (Eptan) sprayed on
the soil and incorporated mechanically
2, 4-DB (Butyrac, Butoxone) applied post emergence
for alfalfa grown in widely-spaced rows for seed production
Glyphosate (Roundup) as directed spray for field bindweed
Trifluralin (Treflan) sprayed and incorporated just before freeze-up
Weed control in established
alfalfa for hay or seed production
Hexazinone applied in the autumn or early spring
for alfalfa grown in widely spaced rows for seed production
Glyphosate (Roundup) as directed spray for perennial weeds
Hand labour as needed to remove surviving weeds.
Summary of Year-Round Weed Management Strategies
Employ sanitary practices;
prevent new weed infestations. Prevent weed shifts resulting from repeated:
• Cultivation (enhances perennial weeds).
• Mowing (enhances prostrate weeds).
• Herbicides (enhances tolerant weeds, new weed biotypes, new micro-organisms that render herbicides inactive).
Identify and Map Your Weeds
• Recognize weeds
with identification books (annuals, perennials).
• Map and record infestations (weed abundance).
• Keep yearly records.
Prioritise Your Weeds by Developing Thresholds
• Highly competitive
weeds (control them).
• Moderately competitive weeds (suppress them).
• Non-competitive weeds (don’t worry about them).
List The Control Methods Gained From:
• Your experience.
• Local experts.
• Published information.
• Learn the strengths and weaknesses of each control method.
Design a Weed Management Programme
Select a field or area
with manageable weed problems.
• Consider the environmental aspects.
• Consider the erosion potential.
• Consider surrounding water, high-value vegetation, or urban and/or recreational areas.
• Consider costs, equipment, management skills, precision timing, and other factors needed to achieve results.
• Develop year-round weed management strategies involving combinations of weed control practices.
Evaluate Your Results
• Evaluate weed management
• Continue mapping weeds for future reference.
Dodder Control in Alfalfa
Dodder is an unique weed, and is particularly problematic in alfalfa seed production fields in Xinjiang. Unlike ordinary weeds that have roots, stems and green leaves, and that carry out their life functions independently, dodder is a parasite. It has no roots nor green leaves (Figure 3). The plant body consists of stems, which must be attached to a host plant to live. In common with ordinary green plants, dodder produces flowers and seeds after reaching an appropriate stage of maturity.
Because dodder is a parasite capable of very efficiently diverting water, minerals and food materials from the host plant to itself, the host plants may be severely retarded, injured and even killed as a consequence of parasitism by the dodder.
Figure 3. Dodder parasitizing alfalfa (left, photo from Certified Alfalfa Seed Council, USA) and common weed (right).
the past 150 years, dodder seed has been disseminated more by human activities
than by natural processes. Because dodder seed resembles seed of forage legumes
such as alfalfa, it is very easy to spread dodder by planting crop seed contaminated
by dodder seed. It is extremely difficult to remove all dodder seed from a lot
of alfalfa seed. It is imperative that alfalfa seed be produced free of dodder
seed, so that dodder will not be spread. Therefore, the only satisfactory level
of dodder control in alfalfa seed fields is 100 percent .
General Methods for Dodder Control Prevention of an initial infestation is the simplest and least expensive means of dealing with a dodder problem in alfalfa. The first step in preventing a dodder problem is planting alfalfa in a field known to be free of dodder. The second step is equally important and involves planting alfalfa seed completely free of dodder seed. Once the field of dodder-free alfalfa is established and growing, care must be taken to prevent movement of dodder seed into the field. This can be done by carefully finding and destroying any dodder growing outside but near the field. Do not move farm machinery to the clean field from dodder-infested fields, and do not allowing grazing animals to move from an infested field to the clean field. Also, dodder seed can move great distances by surface irrigation water or wind movement of infested plant debris.
Although the only completely satisfactory level of dodder control in alfalfa seed fields is 100 percent , alfalfa seed is often produced where the level of control is less than 100 percent . In such fields, the alfalfa seed that is harvested contains dodder seed. Various methods can be used to separate most of the dodder seed from the alfalfa seed. Besides the usual methods of seed separation based on different sieve sizes, special devices have been developed especially for removing dodder from seed of alfalfa and other small-seeded forage legumes. These include the spiral mill, the magnetic separator and the velvet rollers. None of these devices can remove all the dodder seed from alfalfa seed, and unfortunately, they remove a great deal of good alfalfa seed in the process of removing dodder seed.
Destruction of Isolated Dodder Patches: Dodder is frequently found in alfalfa fields as small isolated patches (often representing a single plant) rather than as a general infestation. (Note that a uniform dodder infestation in a field would indicate contamination of the seed used to plant the alfalfa field). Generally, if the total dodder population represents less than 75 patches per ha, and each patch is not more than four metres in diameter, it is usually more economical to destroy the patches individually than to treat the whole field. When an entire field has been treated for dodder control, control is seldom complete. In such fields, the surviving dodder plants (patches) must be treated individually to bring the level of control to 100 percent .
The dodder plant material, together with the host plants to which it is attached, must be burned for total destruction. Stripping of dodder from the host plant is not effective for control, because the dodder can rapidly regrow and produce seeds. The host plants together with all attached dodder can be cut (always below the lowest dodder attachment) placed in a bag or other container, and carried off the field to be burned. In other cases, it might be more convenient to burn the dodder and supporting alfalfa in the field. The patch can be seared with a propane-fuelled torch to kill the foliage. About a week later, the dried material can again be burned so that only a black spot remains where the dodder had been. The alfalfa crown and roots remain alive. A related method involves spraying the dodder patch with a contact herbicide such as paraquat (Gramoxone) to kill the foliage (but not the crown and root). As in the previous method, the foliage is burned completely after about a week.
Any dodder patches found outside but near the field should also be destroyed. Such dodder may be attached to any of a number of weed plants as hosts. Any of the above methods can be used outside the alfalfa field. Another method, often considered better, involves spraying a herbicide that kills completely the host plant and attached dodder. Either glyphosate (Roundup) or 2, 4-D, or a mixture of the two will do this. Areas adjacent to the alfalfa seed field can be planted to a cereal crop, and all broadleaf hosts for dodder can easily be controlled with broadleaf herbicides such as 2, 4-D.
Always, when destroying a patch of dodder in an alfalfa field, it is necessary to destroy some alfalfa foliage beyond the last visible dodder, to be sure any dodder stems hidden by the alfalfa will be killed.
Cultural Methods for Dodder Control: Several cultural methods applied in production of alfalfa, especially alfalfa grown for seed production, can aid in controlling dodder. Planting alfalfa in rows separated by 60 cm or more (as is appropriate for alfalfa grown for seed production) can reduce the dodder problem. This also facilitates discovery and destruction of those patches of dodder that do appear. Because a dodder seedling cannot reach a host plant located 10 cm or more from its point of emergence, the dodder emerging in most of the inter-row area simply cannot reach an alfalfa host plant. If broadleaf annual weeds are eliminated so they cannot serve as hosts, the dodder that emerges between the rows will die soon after emergence.
Light governs the twining growth of dodder stems. Shade from a dense cover of alfalfa foliage can reduce twining by 90 percent or more. In such shade, seedlings do not attach to a host, and those that do attach cannot spread. Open areas in an alfalfa canopy allow light to reach the soil surface and help dodder develop. Therefore, a uniform stand of vigorous alfalfa helps control dodder. Note that this shading effect does not completely control dodder, since dodder can be a major problem in alfalfa grown for forage in Xinjiang.
Most dodder seedlings emerge from seeds on the soil surface or within the top centimetre of soil. If the surface soil is dry dodder cannot germinate. Irrigation management can significantly impact infestations by dodder and other weeds. Frequent irrigation with sprinklers is useful during establishment and early growth, but deep, furrow irrigation is best during pollination. By delaying irrigation, especially the last irrigation before harvest, late-season dodder emergence can be delayed, thereby extending the period of control provided earlier in the season by herbicides. During the period when dry surface soil is preventing germination of dodder seed, the alfalfa foliage is growing, so the dense foliage is able to control dodder by shading until water is applied again.
Many species of broadleaf weeds serve as hosts for dodder. Dodder frequently attaches first to a weed seedling, then spreads to alfalfa. Heat favours dodder seed germination, and light favours dodder seedling development. Consequently, any openings in the alfalfa canopy, such as the spaces in incomplete alfalfa stands of between widely spaced alfalfa rows, are favourable areas for dodder seedlings. If there are no broadleaf weed seedlings in these open areas, the dodder seedlings will die because they have no host.
Control of General Dodder Infestations: When dodder infests so much of a field that spot treatment is not feasible, then the whole field must be treated. Shallow tillage controls dodder effectively. In the early spring, before the regrowth of dodder has become large, shallow tillage can dislodge and bury dodder seedlings. Such tillage also kills broadleaf weeds that could have served as hosts for dodder. Tillage also hastens drying of the solid surface, thereby retarding germination of dodder seed.
The disk harrow is generally not suitable for tillage in alfalfa, because its action injures alfalfa crowns. Other harrows or cultivators that stir the surface soil more gently should be used. Tillage breaks some alfalfa stems, and generally retards alfalfa growth. In alfalfa grown for seed production, such delay does not reduce seed yields.
After a period of tillage in dodder control, an appropriate herbicide should be applied to maintain protection of alfalfa from dodder. Pendimethalin (Prowl) is the most effective soil-applied herbicide for dodder control. Pendimethalin should be sprayed on the soil surface at a rate of two to three kilos per hectare. Rainfall or sprinkler irrigation of 1 centimetre or more moves the herbicide into the surface soil, where it contacts the emerging dodder seedlings and kills them. If two weeks pass after application without overhead irrigation or rainfall, a very shallow tillage will improve the action of pendimethalin. Research has demonstrated that pendimethalin at two or three kilos per hectare applied in late March or early April controls dodder through the month of June. This period of control is adequate to keep the alfalfa dodder-free until seed harvest.
Trifluralin (Treflan) is chemically related to pendimethalin and also controls dodder. The activity of trifluralin against dodder is about half that of pendimethalin. Effective rates of trifluralin are 4 to 6 kilos per hectare. Trifluralin sprayed on the soil surface must be mechanically mixed with the surface soil. Trifluralin is also formulated as granules which contain 10 percent of the active ingredient. The granular formulation of trifluralin is fairly effective without soil incorporation. It has the advantage of passing through foliage to reach the soil surface near the alfalfa crowns.
Crop Rotation: Dodder cannot parasitised any members of the grass family, such as wheat, barley, corn, or any forage grass. When an alfalfa field becomes heavily infested with dodder, rotating out of alfalfa and growing a grass crop is appropriate. Broadleaf weeds must be controlled completely in the grass crop, so they do not serve as hosts for the dodder. Dodder seeds germinate in the grass crop, but cannot live, so no new dodder seeds are added to the soil. During four five years in a grass crop, the amount of dodder seed in the soil will be reduced significantly. However, some dodder seeds usually survive for 10 to 20 years, so some dodder can be expected when alfalfa is again planted in the field.
An Integrated Programme
for Dodder Control in Alfalfa Grown for Seed Production
Dodder is a special weed causing special damage to the crop. Consequently, it demands constant vigilance and special attention. All crop management techniques affect dodder infestations. Clean seed must be planted in clean fields, and fields must be managed diligently. Crop rotation, broadleaf weed (dodder hosts) control during crop rotation, tillage, cultivation, irrigation management, herbicides and harvest methods must be used together (integrated) to effectively control dodder. Any dodder plants detected in or near alfalfa fields must be destroyed.
Early-Season Tillage: Shallow cultivation for two to four weeks early in the season can control dodder. Dodder seedlings are dislodged and buried, and tillage hastens moisture loss form the soil surface, so dodder seeds cannot germinate readily.
Soil-Applied Herbicides: After a period of tillage, an appropriate herbicide should be applied to the soil. Such a herbicide is the most important part of a season-long programme for dodder control in alfalfa. Pendimethalin (Prowl) is presently the most effective soil-applied herbicide for dodder control. Pendimethalin should be sprayed on the soil surfacder germinates. For best results, rainfall or sprinkler irrigation of 1 centimetre or more should follow application within one week. If the field is not so moistened, shallow tillage two weeks after application will improve the action of the herbicides. The period of control initiated by tillage should continue through June as a result of pendimethalin.
Trifluralin (Treflan) also controls dodder, but its level of activity is only half that of pendimethalin. Thus, trifluralin must be applied at a rate of four to six kg/ha to control dodder effectively. Trifluralin applied as a liquid formulation must be incorporated mechanically with the surface soil. If the granular formulation of trifluralin (Treflan TR-10) is used, the herbicide need not be incorporated mechanical
e at a rate of two to three kg/ha before dodly. The granular formulation has the advantage of sifting through the alfalfa foliage to reach the soil near the alfalfa crowns. Applied at 4 to 6 kg/ha, trifluralin should control dodder through the month of June.
Cultural Methods of Control: Alfalfa grown for seed should be planted in rows 60 cm or more apart. Broadleaf weeds can be controlled between the rows by cultivation or with a contact herbicide. Dodder is thereby eliminated as a problem from 60 to 80 percent of the area of the field. When the field is patrolled to detect and destroy dodder that has escaped control, the rows help guide the people walking the fields, and the dodder can be seen easily when it grows into the inter-row spaces.
The last irrigation before harvest should be delayed as much as possible. The soil surface remains dry, and new dodder does not germinate until water is applied. The period of dodder control can thus be extended one to two weeks beyond the period when the activity of the soil-applied herbicide is declining.
Broadleaf weeds must be controlled, so they do not serve as hosts for dodder. The early tillage and the soil-applied herbicides will control many broadleaf weeds. Paraquat (Gramoxone) should be applied between the rows to eliminate any broadleaf weeds between the alfalfa rows. Inter-row tillage will also control such weeds.
Once a week, people should walk through the field to search for dodder. A convenient and effective plan is to walk once in every six rows. A stake should be placed in each dodder patch detected. The patches of dodder so marked with stakes should be destroyed with fire. The infested host foliage with the dodder must be burned completely. An effective method of destroying dodder patches involves first scorching the patch with a gas torch, and then burning the patch a week later with the same torch, so the patch is black and free of all plant material. The method is especially effective if the first operation is cutting the alfalfa below the lowest point of dodder attachment or spraying the patch with paraquat. Thorough burning destroys all the alfalfa foliage, but does not injure the crowns. When the dodder patches are burned, the markers should be left in place, so the patches can be readily found and examined to detect any surviving dodder during subsequent patrolling.
Programme for Dodder
Control in Alfalfa Grown for Hay:
Alfalfa grown for forage production in Xinjiang is frequently infested with dodder. However, alfalfa forage is a less valuable crop than alfalfa grown for seed, and dodder usually reduces the forage value less than that of alfalfa grown for seed. Consequently less money can be invested profitably in dodder control in alfalfa hay fields than in seed fields. Certain inexpensive dodder control measures can be applied in hay fields. Such treatments may not control dodder completely, but will reduce the severity of injury from dodder.
Early-Season Tillage: As in alfalfa for seed, the field can be tilled for a period in the early spring. Because delaying growth of the alfalfa foliage will reduce hay yields, tillage should not continue after it begins to cut or bury alfalfa foliage significantly.
Early Hay Harvest:
To prevent production of dodder seed and to reduce suppression of forage growth,
alfalfa should be harvested early. Cutting the alfalfa in the bud stage rather
than early bloom stage results in improved forage quality, and can prevent seed
production by dodder and other weeds.
Glyphosate Applied to Dodder Patches: After alfalfa is cut, any dodder remaining on the stubble receives full sunlight and begins to grow rapidly. Such dodder is readily detected and should be sprayed with glyphosate (Roundup) at 1.1 to 2.2 g ae*/ha. This extremely low rate of glyphosate does not injure alfalfa significantly, and stops the growth of dodder attached to a host plant. *(ae = acid equivalency: Roundup contains 0.36 kg ae glyphosate per L. Such material applied at 32 to 64 ml per ha will provide the appropriate rate of glyphosate).
Rotate to a Non-Host Crop: If the dodder infestation has become heavy, especially if the stand of alfalfa is incomplete, rotating crops is appropriate. Any grass crop, such as corn, wheat, barley or a forage grass can be grown safely on dodder-infested soil, because all grass crops are immune to dodder. Broadleaf weeds must be controlled in the grass crops to deprive emerging dodder seedlings of any host plants. If the grass crops are grown for four five years without any dodder attaching to broadleaf weeds and producing seed, it should be possible to grow alfalfa again with a much reduced problem from dodder.
Personal Safety The single most important approach to pesticide safety is to read the pesticide label before each use and follow the directions. If still in doubt after reading the label, contact a person qualified to help in evaluating the hazard of the chemical and its use. Qualified people include appropriate specialists and chemical company representatives.
All pesticides are toxic and should be handled with care. Even the most toxic herbicides in the most hazardous circumstances can be used safely provided recommended precautions are followed. The use of protective clothing, respirators, and gas masks may or may not be recommended on the label. To disregard label directions is a violation of the law no matter how you may view the necessity of complying. Obviously there may be disagreement as to how safe is safe enough. It is reasonable to assume that the more toxic a pesticide is, the more protection should be afforded the user, but there are exceptions to general guidelines. A low-percentage granular is less hazardous than the same chemical applied as an emulsifiable concentrate (E.C.). However, the multitude of conditions that could exist cannot be covered on any label. An important increment of safety is that rare ingredient—common sense. Safety should always be carefully considered until it becomes habit; it requires a purposeful, positive attitude. Anything less invites injury or more serious consequences.
Health Hazards. Each season there are accidents, and in some years deaths, attributable to the misuse of pesticides. In case of accidents involving toxic pesticides, see your doctor at once. It will be of great help to your doctor to know exactly what pesticide was involved. The label on the container gives this information. Take along the entire pesticide container, or try at least to have the trade name of the pesticide.
Protective Clothing.Special protective clothing is usually specified on the label when needed for especially hazardous chemicals or application situations. This clothing usually includes one or all of the following: gloves, goggles, face mask, respirator, hard hat, waterproof boots, pants, or hat.
These special precautions are based on the assumption that each person will be appropriately dressed on all occasions when using pesticides. It is obvious that open or porous-weave clothing; bare arms, chest, or legs; and bare feet, sandals, or sneakers provide no protection at all from drift, spills, or other exposure to pesticides. It is equally obvious that rubber boots will provide more protection than fabric cloth, and so on.
The minimum dress acceptable for personal protection and for maintenance of good discipline in handling pesticides includes: long-sleeved, closely-woven shirts, long-legged trousers, work boots, a hat with a brim capable of protecting the back of the neck, and waterproof gloves (waterproof means chemically resistant; the gloves can be made from various synthetic materials). The importance of gloves cannot be overemphasized. Exposure studies of handlers and sprayers repeatedly show that by far the greatest risk of exposure to pesticides occurs on the hands. If a person works daily in the application of pesticides, basic safety discipline (and basic sanitation concepts) also require that the person bathe and launder clothes daily.
Remember, these are minimum safety requirements. “Rubber” (chemically resistant) boots, apron, jacket and trousers, and goggles, face mask, or respirator should be added if one is specifically mixing and loading chemicals.
Take These Precautions
1. If you plan to apply any of the more dangerous pesticides, make sure your physician knows the types of compounds you are using. If you anticipate using the more toxic herbicides, maintain an antidote or at least a copy of the label with you or your physician for immediate action.
2. Wear protective, preferably water repellent, clothing while spraying hazardous materials, because toxic pesticides can be absorbed into the body through the skin. Change and launder clothing and bathe daily.
3. Wear a respirator when loading or mixing concentrates and whenever pesticides may be inhaled.
4. Keep your pesticide storage area locked.
5. Do not smoke, chew tobacco, or eat while spraying. Wash hands before engaging in these activities.
6. Mix herbicides according to directions and precisely apply the recommended rate.
7. Experience shows that poisoning occurs most often in hot weather. Spraying with more toxic materials should be done during cooler periods when possible. Take extra care when spraying during hot weather.
8. Cover crops treated with most pesticides should not be used as pasture or fed to livestock.
9. Agricultural workers should avoid eating unwashed chemically treated fruit and vegetables in the field. The time limitations from application to harvest have been established to protect the consumer from harmful residues. Disregarding these limitations presents a special hazard to the workers in the field.
What to Do in the Event of Poisoning
1. Get the patient to a hospital or physician as soon as possible. Give artificial respiration on the way if the patient turns blue or stops breathing. If you know which pesticide may be involved, take along a label for the doctor’s information. If the label cannot be removed easily, take along the entire pesticide container.
2. Never try to give an unconscious patient anything by mouth.
3. If the pesticide has been swallowed, induce vomiting unless the label directs other action. In the case of a child, induce vomiting by stimulating the throat with the blunt end of a spoon handle, keeping the head in an inverted position.
4. Where excessive amounts of the pesticide, especially in concentrate form, have come into contact with the skin, immediately remove all clothing and bathe the patient with generous amounts of soap and water, rinsing thoroughly.
5. If the eyes have been contaminated with spray, especially with pesticide concentrate, flush immediately with copious amounts of water, preferably with running or flowing water.
6. Make the patient lie down, and keep the person warm.
Pesticide Spills and Cleanup Pesticide Spills. Pesticide spills and cleanup require immediate action based on foresight and preparation. All reasonable precautions should be taken to avoid spilling pesticides, but accidents will occur. Accidents are most likely to happen when pesticides are being transported or in a storage area. A spill kit carried in vehicles and kept in pesticide storage areas will allow quick and effective response to spills.
Some important items in a typical spill kit include:
1. Protective clothing
2. Adsorptive clay
3. Plastic bags and bucket
5. Fibre brush and screw-in handle
6. Dust pan
7. Highway flares
Response to a pesticide spill may vary with size and location of the spill, but the following are usually appropriate:
1. Control traffic.
2. Dress clean-up team with protective clothing.
3. Stop leaks.
4. Contain spilled material.
5. Clean up and remove spilled pesticide and contaminated adsorptive material and soil.
6. Transport spilled pesticide and contaminated material to a disposal site.
Safe use of Herbicides
Herbicides should only be used when necessary, at recommended rates and times of application, and only for those crops and uses listed on the label. Correct use is essential to ensure that chemical residues on crops do not exceed the limits set by law. Recommended herbicides will not generally cause injury to people, livestock, wildlife, crops, or the environment if used according to label directions. Any pesticide is potentially dangerous if improperly handled or misused.
Following these basic safety procedures will help you protect yourself and others from pesticide injury:
1. Make sure that you are familiar with current federal and local pesticide laws.
2. Make sure that you have the proper pesticide applicator license, if required.
3. Avoid herbicide drift that may endanger other crops or animals. Cover feed pans, troughs, and watering tanks in livestock areas. Protect beehives when using insecticides.
4. Follow all safety precautions on the label. Know and observe the general rules for safe pesticide use.
5. Record the date, time, location, amount of each pesticide used, and weather data for each spray operation.
6. Wear proper protective clothing and use protective equipment as instructed on the label.
7. Never eat, drink, or smoke while applying pesticides.
8. Immediately wash off all pesticide spills on clothing or skin with detergent (which cleans better than soap) and water. A supply of clean water should be on hand when handling pesticides.
9. Bathe after pesticide application and launder clothing separate from other laundry.
10. Lock pesticides in original containers in a properly marked cabinet or storeroom separate from food, feed, or fertilizer.
11. Store herbicides separate from other pesticides to avoid contamination.
12. Triple-rinse all empty containers and use the rinse water as part of the spray solution. Empty containers should not be used for any other purpose. Dispose of empty containers in a proper manner.
13. Be familiar with basic first-aid procedures involving pesticides.
14. If you suspect pesticide poisoning, contact the nearest Poison Control Centre, hospital emergency room, or physician. Be sure to take the pesticide label with you and give it to the attending physician.
Livestock. Herbicides sprayed on plants are not generally toxic to livestock; however, animals may be poisoned by eating unused herbicides left in open containers or by drinking water contaminated with herbicides.
Certain unpalatable or poisonous plants treated with certain herbicides may become palatable to livestock. Be certain that livestock are kept out of areas where poisonous plants have been sprayed until the plants have dried up.
The nitrate content of several kinds of plants may increase after they have been sprayed with 2,4-D, dicamba, or similar herbicides. Cattle browsing on these treated plants may be poisoned.
Pay attention to grazing restrictions outlined on the label. The restrictions will prevent illegal residues that could prevent the meat from being marketed.
Wildlife. Controlled spraying may benefit wildlife by maintaining desirable cover. Herbicides recommended for control of aquatic weeds usually have beneficial results for fish populations. Be sure to use these herbicides properly. Don’t drain or rinse equipment where chemicals may wash into waterways.
Groundwater Groundwater is the source of water for wells and springs. It fills spaces between particles of soil or cracks in bedrock. Geologic formations containing groundwater are called aquifers. Groundwater is widely used for household and other water supplies.
Four major factors determine whether a pesticide is likely to reach groundwater: (1) properties of the pesticide, (2) properties of the soil, (3) conditions of the site, and (4) management practices.
Properties that affect a pesticide’s potential to contaminate groundwater are:
a) Solubility. Highly soluble herbicides have a tendency to be leached from the soil to the groundwater.
b) Adsorption. Many pesticides do not leach because they are tightly adsorbed by soil particles.
c) Volatility. Highly volatile herbicides that are not water soluble will be lost to the atmosphere and less will be available for groundwater contamination.
d) Degradation. Herbicides that breakdown rapidly in the soil are less likely to be leached into the groundwater.
2. Properties of a soil that affect its potential to leach are:
a) Soil texture. The coarser-textured a soil, the greater the chance of the herbicide reaching groundwater.
b) Soil permeability. Highly permeable soils will increase the chance of a herbicide reaching groundwater.
c) Organic matter content. Soils high in organic matter will adsorb herbicides, decreasing the chance that they will contaminate groundwater.
3. The conditions of a site that affect its potential to contaminate groundwater are:
a) Depth to groundwater. The shallower the depth to groundwater, the less soil there will be to act as a filter. If rainfall is high and soils are permeable and have a low adsorptive capacity, water carrying pesticides may take only a few days to percolate downward to groundwater.
b) Geologic conditions. The permeability of the geologic layers between the soil and groundwater is also important. Highly permeable materials, such as gravel deposits, allow water and dissolved pesticides to freely percolate downward to groundwater.
c) Climate. Areas with high rainfall or irrigation may have large amounts of water percolating through the soil. These areas are highly susceptible to leaching of pesticides, especially if the soils are highly permeable.
4. The management practices in a particular area can have an effect on the potential of pesticides to contaminate groundwater.
a) Application methods. Injection or incorporation into the soil makes pesticides more available for leaching. Most of the pesticides that have been detected in groundwater are soil applied and incorporated rather than being sprayed onto foliage.
b) Pesticide rates and timing. The rate and timing of a pesticide’s application also are critical in determining whether it will leach to groundwater. Excessive rates (and the closer the time of applications to heavy rainfall periods or irrigation) increase the possibility that pesticides will reach the groundwater.
Use the following guidelines
to help prevent groundwater contamination:
— Are pesticides really necessary or is there another way to control the pest?
— Identify the vulnerability of the soil. Is the soil subject to leaching, i.e., a well-drained sandy soil low in organic matter?
— Consider the location of the pesticide application in relation to ground and surface water.
— Become familiar with pesticides that leach.
— Follow the directions on the pesticide label. Don’t use more than the recommended rate.
— Apply the pesticide at the proper time. Fewer applications may be required if weeds are sprayed when small.
— Calibrate and maintain equipment.
— Avoid spills and back-siphoning into wells or water supplies.
— Direct the application to the target site.
— Dispose of the pesticide properly.
— Store pesticides safely. Keep away from pumps, wells, and other water sources.
— Keep accurate records of pesticide use.
— Where possible, delay irrigation after pesticide application. Delaying irrigation for one or more days after applying a pesticide can minimize the chances of the pesticide reaching groundwater.
— Avoid irrigation runoff.
— Use particular care when practicing chemigation. Devices must be used to prevent possible back siphoning of the pesticide into the water supply.
— Properly seal new
wells and inspect old wells to ensure that the seal is adequate.