Soybeans are susceptible to attacks by various diseases and pests throughout their growing season. All pests have the ability of decrease soybean yield. Brown leaf spot, frogeye leaf spot, brown stem rot, stem canker, purple seed stain and pod and stem blight are major soybean fungal diseases. Bacterial blight, pustule, wildfire and wilt are major soybean diseases caused by bacterial. Major viral diseases include soybean mosaic, yellow mosaic, bud blight and bean pod mottle. Soybean cyst nematode and root knot nematode are the main species of nematodes that attack soybeans (Liu, 1997). The causal organisms of soybean diseases in the top 10 soybean producing countries during 1994 are shown in Table 23. Insects are serious pests, particularly in tropical and subtropical areas, because they feed on all parts of the soybean plant. Larvae of lepidoptera (moths) and coleoptera (beetles) are two major groups that attack soybean foliage. Within the lepidopterous larvae group, green cloverworm (Plathypena scabra, Fabricius), soybean looper (Pseudoplusia includens, Walker), velvetbean caterpillar (Anticarsia gemmatalis, Hubner) and corn earworm (Heliothis zea, Boddie) are four major species that often cause problems to soybean farmers. Stink bugs (Acrosternum hilare, Say), alfalfa hopper (Spissistilus festinus, Say) and lesser cornstalk borer (Elasmopalpus lignosellus, Zeller) are the major pod- and stem-feeding insects. Other pests attacking soybeans include birds and rodents. Birds and rodents attack soybean most often immediately after planting.

Rotating crops, spraying chemicals and choosing resistant cultivars brought about by plant breeding and have been the major tools used by farmers to control diseases and pests. Among all practical methods of insect pest control, planting cultivars resistant to insect pests is the most economical, sustainable and environmentally acceptable (Talekar, 1997).

Among the recommended disease management practices are the use of resistant varieties (Ivancovich et al., 1993) and crop management such as crop rotation, tillage and planting date (Ivancovich et al., 1997). Diseases than can be reduced by crop rotation are those caused by bacteria; fungal foliage diseases- Alternaria leaf spot, anthracnose, Septoria brown spot, Cercospora leaf spots, Choanephora leaf blight, Phyllostictia leaf spot, red leaf blotch; fungal diseases of roots and lower stems- brown stem rot, charcoal rot, pod and stem blight, Sclerotinia and Sclerotium blight and stem canker; and nematode diseases- root knot and cyst (Sinclair and Backman, 1989).

The use of chemical compounds is another alternative to control weeds, diseases and pests. In general, they are known as pesticides. A complete list of pesticides tolerance levels for soybeans is given in the Annex. The chemical compounds (pesticides) used to control weeds are called "herbicides", those used to control insects are called "insecticides" and those used to control fungal diseases are called "fungicides".

The groups of pesticides are chlorinated hydrocarbon, organo-phosphorus, carbamates and pyrethroids. Pesticides are used in the form of spray, dust, granules and seed dressing. Fungicide seed treatment is an alternative to control soybean diseases in several countries. In Brazil, the use of fungicides for seed treatment has increased since 1991. In the 1991/92 soybean crop, about 5 percent of the cultivated land used seed treated with fungicides, whereas in the 1999/2000 crop more than 85 percent of the cultivated area used treated seed (Http://www.cnpso.embrapa.br). About 30 fungicide formulations used to treat soybean seed (1999/00 crop), among commercially available and others, were reported. In Argentina, fungicide seed treatment is a recommended practice since efficiently controls most of soybean seed diseases (Larreche and Firpo Brenta, 1999).

The use resistant cultivars to the attacks of different insects have been developed. Recently, a soybean cultivar with resistance to white fly, the devastating insect that caused severe yield losses in the Northwestern part of Mexico, was developed (Castillo et al., 1998). Some other resistant cultivars were presented in Section 2.1. The cultivar "Hartwig" is probably the best source of resistance to the cyst nematode, Heterodera glycines (de Toledo et al., 1997). Duyn et al. (1971) reported genes for insect resistance in PI 229358, PI 227687 and PI 141451.

Cultivars with resistance to some diseases have been developed and used in most of the soybean producing countries. Brazil has several cultivars with resistance to stem canker disease (Diaporthe phaseolorium f. sp. meridionalis). Brazilian cultivars with resistance to this important soybean disease are BR-1, Doko, CAC-1, Dourados, EMGOPA 302, FT-Estrella, IAC-13, IAC-17, MTBR-45 and UFV-9 (de Toledo et al., 1997). Another resistant cultivar to stem canker is Tracy M (Kilen and Hartwig, 1987).

Biocontrol of plant diseases is accomplished through the use of resistant cultivars, crop rotation, clean tillage practices or organic manures (Schippers et al., 1987). The use of successful biocontrol agents for soybean is still being investigated. A potential biocontrol agent for a soybean disease (caused by Rhizoctonia solani) is seed or soil treatment with Bacillus megaterium strain B153-2-2 (Liu and Sinclair, 1990, 1991). Another example is the use of Bacillus cereus Frankland & Frankland, strain UW85, as a seed treatment to reduce soybean seedling damping-off caused by Phytophtora spp. (Handelsman et al., 1988). In Brazil, the widespread use of the virus Baculovirus anticarsis has shown some success to control A. gemmatalis (Panizzi, 1997). Also, the liberation of one species of parasitoid, T. basalis in the field (5 000 adults/ha) has proved to be efficient to maintain stinkbug populations below the economic injury level (Correa-Ferreira, 1993).

Maintaining adequate availability of plant nutrients and proper soil pH, supplying adequate water, weed control, avoiding excessive plant density and planting high-quality seeds are effective in reducing damage from many diseases.

Most research on integrated pest management (IPM) for soybean has been taking placed in the temperate zones of North America, South America and the Orient (Kogan et al., 1988). The components and a generalized scheme of an IPM program were reported by Kogan (1997). IPM programs have been successfully implemented in countries such as the United States, Brazil and Argentina. However, widespread adoption of comprehensive IPM strategies is yet to occur anywhere in the major soybean growing regions of the world. In Brazil, the implementation of IPM systems leaded to a drastic reduction (over 75 percent) in the amount of insecticide used, use of low dosage (half recommended dosage of commercial insecticides with the addition of sodium chloride to the solution) to control stink bugs.

Moulds and insects are the primary causes of quality deterioration in stored soybeans. Both are favoured by high moisture and warm temperatures, as well as the presence of damaged grain and excessive foreign material in the soybeans. The insect pests which are known to cause damage and loss to soybeans are almonds moth, (Ephestia cautella (Walker), tobacco borer beetle (Lasioderma serricorne (Fab.), red grain beetle (Tribolium castenum (Herbst), T. confusum Kackuelinduval, khapra beetle, Trogoderma granarium Everts and pulse beetle, Callosobruchus analis Fab. and C. chinensis (L.). The beetle pests fail to develop on whole seeds but can multiply slowly on broken seeds. Fungi can also damage soybeans and soybean meal during storage if the moisture content of these materials is in equilibrium with relative humidities from 65 to 70 to 85 to 90 percent. Table 26 shows the equilibrium moisture contents of soybeans and soybean meal at 65 to 90 percent relative humidity (25 ° C) and fungi likely to be encountered.

Source: Sauer et al. (1992).

Pesticides most commonly used to control pests in stored soybeans and soybean products are shown in Table 27. In grain storage, the primary pesticides utilized are insecticides, including grain protectants, residual sprays and fumigants. One of the most important sources of insect infestation is residual grain in the storage bin or storehouse. It is very important to remove all trash from the bin or storehouse and the surroundings before insecticide treatments are applied. A common practice in a crushing industry in Mexico, which utilizes a similar storage facility to that shown in Figure 19 (left), is to sweep the floor and walls of the building with diesel to remove dust and to drive away insects. Once the bin is clean, it can be treated with chlorpyrifos-methyl, synergised pyrethrins, cyfluthrin, or methoxychlor before the grain is loaded. Phosphine-producing materials and methyl bromide are the two fumigants permitted for treating stored products. Fumigation is needed when no other pesticide or control method can reach the insect infestation. Fumigation is the most hazardous type of pesticide treatment, it is expensive, provides no long-term residual protection and may cause resistance problems if conducted repeatedly. Some industries do not have trained personnel to fumigate the storage facility; therefore, they have to contract the service of fumigation companies to get the job done. In large bulk storage facilities where methyl bromide is used, some type of recirculation system is usually employed to achieve an even distribution of the fumigant after application. Fans can be used to distribute methyl bromide in smaller facilities. Respiratory and detection equipment is mandatory when using methyl bromide. Cans of methyl bromide can be used to fumigate a small space, but they require a special "can opener" often called a "Jiffy" or "Star" opener. These openers puncture the can and allow the methyl bromide to escape through polyethylene tubing. Before the can is opened, the tubing can be inserted into a rail car, truck trailer, bin plenum, or fan housing (Leesch et al., 1995). Steel cylinders can be fitted with special metering devices to fumigate small places, such as rail cars, or the gas applied can be measured by loss of weight from a cylinder. It is necessary to seal the bin or the storehouse containing the soybeans before start fumigation. Once that the fumigation has been accomplished, the sealed bin is left undisturbed for 24 hours and then opened to air out. Turning on the bin fan will help remove the fumigant quickly from the bin. Detection equipment must be on hand to determine when the concentration falls below 5 ppm (0.02 g/m³) for re-entry into the facility. One advantage of methyl bromide over phosphine is that methyl bromide requires less time to kill insects than phosphine. While phosphine requires from 3 to 10 days, depending on the temperature, methyl bromide exposure time usually ranged from a few hours to one day.

Keeping the grain at low moisture and temperature can prevent moulds growth in stored soybeans. Removing caked and obviously moulded grain from storage bins or storehouses and disinfecting the storage facility is another way of preventing soybean spoilage during storage.

Rodents can also deteriorate soybeans during storage. Effective control of rodents in the storage facilities requires an integrated approach that involves sanitation, rodent-proof construction and population reduction (Hygnstrom, 1995). Sanitation can be as simple as cleaning spilled grain or products in rodent-proof buildings, rooms, or containers whenever possible. Stack sacks of grain or products on pallets with adequate space left around and under stored articles to allow for inspection for sign of rodents. The most successful and permanent form of rodent control is not allowing them to have access to the building. It is recommended to use a 1/2 x 1/2 –inch galvanized hardware cloth to screen ventilation openings. Rodenticides are used to control mice and rats when population exceeds tolerable levels. Rodents can also be killed with methyl bromide; only one-fourth pound per 1 000 cubic feet is required for 12 to 24 hours. Phosphine and chloropicrin also kill rodents.

Source: Code of Federal Regulations (1997).

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