Organisation:Food and Agriculture
Organization of the United Nations, FAO, Rome,
Italy
Author: Lidia Dorantes, PhD., Lidia Parada, MSc., Alicia Ortiz, PhD.
Edited by AGST/FAO: Danilo Mejía, PhD, FAO (Technical), Emanuela Parrucci
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3. Pest control and decay
3.1 Pest species
3.2 Relative status of major pest species
3.3 Pest control
3.4 Others
Pests have an economical impact on the avocado producer as they damage the branches, trunk, leaves and fruit. Pests are also a cause for quarantine restrictions when the fruit is exported.
Mexican avocado overcame the last sanitary barrier for its exportation to the United States, which limited its global commercialization. Since 1990, negotiations began with this country and, as a consequence, local, regional and state sanitary commissions were established, which began gathering information regarding infestation zones, population dynamics, biological cycles, as well as control and eradication techniques of quarantine pests (Morales, 2000).
In Chile, the change of Chilean avocado varieties to Hass variety has not meant an important change in the diversity of pest species that affect the fruit, but a change of the importance of each pest on the crop. Even though 31 species of insects are potentially harmful to Chilean avocado (Prado, 1991), only 9 species are considered as economically important (González, 1989) and among them, often only 1 or 2 species will be relevant for a particular crop. Most of the times, no chemical substances are needed to control them.
In Mexico, some authors reported different numbers of pest species of importance for avocado crops, for example, SAHR-DGSV (1981) mentioned 12 as important pests, Gallegos (1983) reported 46, and Coria (1993) enlisted 11 species for Michoacán. However, as it is the case in Chile, only few pest species are economically important for avocado crops (Téliz, 2000), except in areas with deficient handling, lack of problem diagnosis, and inadequate application of labor and supplies. Avocado pests affect 14% of avocado production and diminish the fruit quality in 10%, which increases the costs in 23% (Vidales-Fernández, 1999).
The International Sanitary Certificate is required at the sanitary inspection booths in order to permit the exportation of avocado. In Mexico, the orchards must be registered in the Agricultural Ministry and the producer must register all the activities related to the prevention and control of pests in a "Sanitary Calendar" (Morales, 2000).
Avocado root-rot, Phytophthora cinnamomi Rand. Root-rot is the most important disease of avocado in the world. In Michoacán, it is present in every cultivar, affecting 5% of the total surface of crops. Phytophthora is one of the most pathogenic fungi in the world and causes the death of trees (Vidales-Fernández, 1999). As a first symptom of the disease, the foliage of the affected trees begins to decay and discolor to yellow. The leaves start to fall down until only the branches remain. Sometimes, a recovery can be observed in the dry season, when applying a nitrogen-rich fertilizer and fungicide to the ground. As a consequence, the farmers do not follow the recommendations of uprooting and disinfecting the trees, and thus the disease spreads around.
The Wurtz variety has a high tolerance to this fungus, growing in affected areas without any symptoms, and it is uncommon to lose this kind of tree to the disease. Some hybrid trees ("criollos") are also resistant, and efforts to preserve them have been enforced (Morales, 2000).
Avocado blight, Sphaceloma perseae (Myriangiales: Elsinoeaceae). It is found throughout Michoacán and it is considered an endemic pest. Avocado blight or "roña" is also found in Florida, where it is the second most important pest, Puerto Rico, Brazil, Africa, Peru, Cuba, Haiti and California.
The Sphaceloma perseae fungus attacks the fruit (in all stages), leaves, and young branches. The affected fruits present brown lesions of corky aspect with round or irregular shapes at first (Figure 34 Fruits affected by avocado blight or "roña").When these lesions grow and come together, they can cover a large part of the fruit or the whole fruit, and cause fissuring in leaves and branches. In leaves, the pest forms small individual stains of dark brown color of less than 3 mm in diameter when the attack is severe, the leaves and nervations are also distorted. In nervations or green branch barks, the lesions are elongated and slightly prominent. In the fruit, the damages are exclusive of the exocarp, while the fruit remains healthy. However, the lesions can be an entry point for other organisms (Gallegos, 1983).
The S. perseae conidia have a size of 2.3 to 2.5 mm, with a cylindrical to oblong shape. The color of the colonies is variable, from grayish white to dark gray and darker with age, as opposed to the Colletotrichum colonies, which have a salmon color (Marroquín-Pimentel, 1999).
The S. perseae fungus requires a high relative humidity and high temperatures for its proper development. The most susceptible stage of the fruit is when it reaches a third or a half its normal size, because when the fruit ripens, the exocarp hardens. The damages of the fruit caused by insects, rodents or mechanically allow the entrance of the pest, which produces spores on the attacked tissue. The spores are carried away and disseminated by the wind, rain or insects.
Source: Sanidad Vegetal de Salvador Escalante Michoacán, México
From all the cultivars grown in the Michoacán region, "Fuerte" is the most susceptible to the disease. "Hass" can also be severely affected if the pest is not prevented. Booth 1, Pollock, and Waldin are considered slightly susceptible. The local hybrids ("criollos") are also likely to be affected by the fungus, although the incidence is lower because the fruit from these trees ripens in the spring (Gallegos, 1983).
Thrips Liothrips persea Watson, Scirtothrips aceri Moulton, Frankiniella cephalica, Heliothrips haemorrhoidalis (Insecta:Thysanoptera: Thriphidae). Similar to the red mite complex, the thrip pests are constituted by several species in every region. They are found in Florida, California, Mexico, Central and South America, Argentina and Chile. Thrips have a stronger presence in tropical and subtropical coastal zones, and their damage is reduced in the avocado cultivars located between 1900 and 2400 m of altitude.
Thrips are small insects, 0.3 to 14 mm in length, and white or pale yellow to dark brown in color. One of their main characteristics is two pairs of long wings that sometimes cover the abdomen. They have a sting-sucking mouth apparatus (Ullman et al.,1992). Johansen et al (1999) published a taxonomic study of 41 Mexican species of insecta Thysanoptera inhabiting Persea americana Mill floral and foliar structures. They reported that a total of 38 species are phytophagous, whereas only three are predators. Only six phytofagous species can be considered as primary pests for the young fruit or foliar structures, and the other 32 can be considered as incidental visitors. The three predatory species live in both natural ecosystems and avocado agricultural ecosystems. The cacao thrips, Selenothrips rubrocinctus, and greenhouse thrips Helipthrips haemorrhoidalis, are the most common and relevant for avocado in the world. These species are poliphagous and have a worldwide distribution (Lewis et al.,1997).
All the species survive on foliage, by scraping and sucking the superficial cells, thereby causing the appearance of discolored spots, which are silver-white at firs, and later turn dark. This is observed more often on leaves and fruits, however, they can also be found on tender shoots, buds, and flowers. The damages produced by this pest can make the crop loose up to 50% of its commercial value (Adame, 1994; Gallegos, 1983).
Thrips are one of the most relevant pests for avocado cultivars in Mexico. They can cause malformation of the fruits, (Figure 35 Avocado affected by trips) premature falling from the tree and damage the vegetal tissues when feeding, producing lesions that become entry points for microorganisms such as Sphaceloma perseae (González-Hernández et al.,1999). The major damage is caused when the thrips feed on young fruits, producing crest-shaped malformations of the exocarp, which are more evident in ripe fruits Coria (1993) mentioned that some types of weed, such as Asteraceae, are alternative hosts for thrips.
Small seed weevil, Conotrachelus perseae Barber (Coleoptera: Curculiondae: Cryptorhynchinae). It is found in the eastern central region of Mexico and northern parts of Central America, Guatemala, and Panama.
The adults are typical beaked weevils, dark brown in color, average size 7 mm, capped antenna with geniculated base. They emerge from pupae in the soil at the beginning of the rainy season. The females lay their eggs in the surface of the fruit. The eggs are transparent at first, turn to grayish white, and hatch after 6 or 7 days of incubation, measuring approx. 0.8 to 1.0 mm. The larvae are of yellowish white color with a dark cephalic capsule, and reach a length of 6 mm. They tunnel, forming a gallery throughout the pulp until they arrive at the seed, which is usually destroyed (Figure 36 Avocado damaged by large seed weevil)
The larva cycle lasts from 18 to 20 days, followed by the prepupa that lasts from 22 to 23 days, and then the pupa that lasts for 13 more days. The larvae in their last stage leave the fruit and fall down to the ground, where they form a cocoon of about 5 cm beneath the soil.
The adults are nocturnal in habits and feed on leaves, fruit, and tender branches. During the day they rest in the hollow of coiled leaves, leaf axis or inflorescences. The cycle from egg to adult lasts about 78.5 days for the female and about 76.5 days for the male. Their life span can be up to 140 and 111 days respectively, with two generations per year, but generations can overlap.
Highly infected areas can affect up to 85% of the fruit, destroy the seeds and notably affect the production since this situation induces the falling of the fruit from buds to maturity (Llanderal and Ortega, 1990; Martinez et al.,1987).
Large seed weevil, Heilipus lauri Boheman (Coleptera: Curculionidae: Hylobiinae). It is found in the western central region of Mexico, but not in the avocado cultivars of Michoacán. Other species of this weevil are H. sguanosus found in Florida and California, the Antilles, and in the Virgin Islands; H. pihieri in Central America; H. cartagraphus and H. montei in Brazil; and H. persea in Panama.
The adults are large beaked weevils, 12 to 15 mm in length, of bright reddish-black color with a rough dorsal section, and elytra with 2 yellow stripes that is more noticeable in males, which are slightly smaller than females. Females lay 1 to 2 oval-shaped eggs in a previously made cavity under the epidermis of the fruit, which at the first are green in color and later become darkened. The eggs incubate from 12 to 14 days, and then the larvae are hatched. The larvae are curved in shape, legless and of a creamy white color. They go through five instars in a period to 54 to 63 days, and they reach a length of 12.5 to 25 mm. They tunnel through the flesh of the fruit, forming a gallery that extends to the seed, which is usually destroyed. Furthermore, they produce secondary rotting of the flesh and the seed. The pupae develop inside the fruit after 14 to 16 days, in some cases leaving the fruit and forming chrysalis in the ground. The adults have a life span of 3.4 to 4 months; they feed on leaves, buds, sprouts, and fruits, producing 2 generations of insects per year.
This pest affects up to 80% of the production as they destroy the flesh, seeds, and cause a premature falling of the fruits (Bravo et al.,1988; Gallegos, 1982)
Seed moth, Stenoma catenifer Walsingham (Lepidoptera: Stenomidae). This is one of the most widely distributed avocado pests in Mexico, being found in the east and coastal zones of the country. It is also found in Guatemala, Costa Rica, Panama, Colombia, Venezuela, Peru, Bolivia, Ecuador, Brazil, and Argentina.
Young adults are yellowish colored moths, and later change to a grayish-brown color. They measure 7 to 9 mm, with a wing length up to 25 mm. The forewings have 25 dark spots that form an "S" shape across the wing. These insects have night habits and mate after 1 or 2 days of their emergence, and lay their eggs a day after mating. The eggs are deposited on or near the fruit, and also on tender branches. The eggs are semi-spherical in shape, light-green colored, and no longer than 0.6 mm. Upon hatching, whitish larvae emerge and penetrate the fruit forming galleried which extend to the seed, and in branches extend to the central cylinder. They pass to 4 or 5 instars that last from 15 to 19 days. In the last of the instars they turn purple on the dorsal side and blue in the abdomen, reaching a maximum size of 18 to 22 mm. They abandon the fruit, which by this time is usually fallen in the ground, where pupation takes place, lasting for a period of 8 to 12 days, in a depth of 2 to 5 cm. The adults emerge and live an average of 8 days. The average life cycle is 46 days with 3 generations per year.
Seed moths can penetrate fruits of any size and destroy the seed completely. The galleries they form inside the branches cause withering, reduce flowering of the tree and seriously damage up to 90% of the production (Bravo et al.,1988; Gallegos, 1982; García-Martel et al.,1983).
Red or brown mites, Oligonychus (Homonychus): Opunicae hirst, O. yothersi Mc. Gregor, O. platani Mc. Gregor, and Eotetranychus sexmaculatus Riley. Acarina: Tetranychidae. The insect complex designed as red or brown mite is present in most of the avocado producing countries, different kinds prevailing in accordance to environmental and climatic conditions. For example, O. punicae is the most widely distributed, being found in California, Florida, Brazil, Argentina, Colombia, Ecuador, Chile and Central America. O. platani is found in the states of California, Arizona, and Texas, as well as in Coahuila (in the north of Mexico). E. sexmaculatus is found in California, Florida and Arizona.
O. punicae attacks the surface of leaves, mainly near the nervation where dusty-like colonies are formed. The adults are oval in shape, slightly elongated, of pink color and have purple or brown spots on the lateral areas of the abdomen. The males measure 0.3 mm and the females 0.4 mm. They lay eggs throughout the nervations and incubate for a period of 7 to 10 days. At hatching, the larvae are colorless, with six legs, and no larger than 0.1 mm. The instar lasts form 2 to 3 days, at the end they become protonymphs of pink or pale green color, double the size of the larvae and last for 2 days. Afterwards, they enter the neutonymph stage and turn a little darker but are still transparent. They increase in size to 0.2-0.3 mm, have 8 legs and last for 2-3 days. Upon concluding the nymphal stages, the insects reach adulthood having 8 legs, and a life span of 15 to 45 days, depending on climatic conditions. The total life cycles varies from 30 to 60 days.
These mites attack the surface of leaves, produce abundant colonies and hibernate as eggs. The adults emerge at temperatures of 15.5 to 21ºC, however, their best development and greater longevity happens at 26ºC. The attacks to the trees are more severe during the dry season, with a relative humidity lower than 60%. Rain severely affects these mites, violently decreasing their population at the beginning of the rainy season.
When sucking the sap out from the cells, the mites alter the proportions of chlorophyll and photosyntates, which produces the chlorosis symptom: brown coloration of leaves and defoliation. Furthermore, the carbon-nitrogen ratio is altered which reduces the production of growth elements. This results in the reduction of budding, flowering, foliage development, and consequently, the fruit production for the next season (Arias, 1984, Eveling, 1959, López, 1990).
White fly. Trialeurodes floridensis Quaintance, Tetraleurodes sp., Paraleyrodes persea Quaintance. (Homoptera: Aleyrodidae). White flies are an endemic pest of worldwide distribution. However, their attacks are more severe in regions with warm and humid climates, such as tropical coastal regions. They are present all year long, and it is during the months of spring and summer (rainy season) when their population is increased to important levels that require control. In the avocado growing regions of the Americas, white flies are found in Florida, Mexico, Central America, the northern part of South America, and of less importance in California, Chile and Argentina.
Paraleyrodes persea is the most widely distributed species in the Mexican avocado cultivars. The adults are small white moths, from 1.5 to 2.5 mm in length, with four wings covered by a white waxy powder. They form white powdery colonies of circular shape 1.0 to 1.5 cm in diameter. The females lay numerous white eggs of approximately 0.3 mm. A mobile oval nymph of yellowish-green color is hatched and after 5 days the legs fall off, it attaches itself to the leaf and turns black. The sides have short waxen filaments. In these immobile forms the insect passes two instars of 6 to 7 days, feeding on the tree sap. The complete nymphal period can vary from 18 to 30 days in the summer, and from 20 to 42 days in the winter, producing 3 generations per year.
In severe attacks, 15 or more colonies can be formed in the back and in the surface of the leaves, indicating the intensive sap absorption. The attack is usually stronger in the mature and lower leaves of the tree, causing intense defoliation. Chlorotic cycles of yellowish color are observed and the fruit production is reduced. The abundant wax secretions of the colonies are often associated with the growth of molds (Martinez, 1984).
Dog worm or swallow wing butterfly. Papilio garamas garamas Hübner, Papilio victorinus merelius Rothschild and Jordan, Papilio crespontes Cramerg (Lepidoptera: Papilionidae). Dog worm is widely distributed in the citrus and avocado zones of America. Its incidence is greater in tropical and subtropical zones, and much lesser in high zones.
The adults are medium to large size butterflies with a wing span of 8 to 10 cm. There is sexual dimorphism in wing size and color. They are black with parallel yellow stripes and arched on the distal edge of the wings. The back wings have prolongations in the posterior region, from which the name "swallow wing" originates. The eggs are light green in color, usually measure 1.8 mm in diameter, and are laid on the surface of the leaf near the central venation. Incubation lasts from 10 to 14 days. The larvae are small and voracious, quickly increase in size and go through 5 instars. They secrete a substance based on valerianic acid that gives them a strong, disagreeable odor that works as defense and protection. The 5 larvae instars last for 40 days, after which they pupate forming a chrysalis of 4 cm in length, with a grayish brown tip. They attach themselves to the end of a branch by weaving a silky thread around the branch and the pupae. This phase lasts an average of 25 to 40 days before the insect emerges as an adult.
Dog worms are voracious defoliators, generally of gregarious habits, but a few of the larvae of the last instars can completely devour the foliage of a medium size tree. Fortunately, in avocado orchards their incidence is low, isolated and only happens in the summer (from July to September). The affected trees can loose their flowers and fruit production for the following cycle (Bravo, 1988; Del Rio, 1978).
Leaf roller worm and Amorbia moth (called "gusano descarnador" in spanish) Amorbia emigratella Busck, A. cuneana Walsingham, A. essigana Busck (Lepidoptera:Tortricidae). The various species of Amorbia can be found in California, Mexico, and Central American countries such as Guatemala, Costa Rica and Panama. It is an endemic pest, present in the summer months.
The adults are small moths from 2.5 to 3.0 cm in length and reddish-brown in color. The males are slightly smaller, with dark triangular spots in the center of the front wings, and dark distal edges. They are nocturnal in habits and have a life span of 15 to 20 days. The females lay eggs on the surface of leaves: masses of light green eggs in overlapping layers that require 13-15 days to hatch. The larvae go through 5 to 7 instars, which are differentiated by their color and size. In the first instars, they are yellowish-green in color, from 2 to 3 mm, and in the last they are dark green, from 20 to 30 mm. When they are bothered, they let themselves fall down suspended by a silky thread, which they use to roll up the leaves or fruits, and sometimes 2 or 3 larvae can be found together. The pupae measure an average of 18 mm and are green at first, later turning brown, and last for an average of 17 days. The complete life cycle varies from 98 and 120 days depending on the location and season of the year. This insect produces 2 or 3 generations per year, however, only one generation is enough to produce important damage.
The damage is caused by the larvae, when destroying a large amount of foliage and tender shoots. (Figure 37 Leaf roller worms and Amorbia moth affects avocados).
More important is the damage done to the fruit, since they frequently bind together fruits and/or leaves with their webs, taking shelter and feeding of them, producing injuries that can favor secondary rotting (Bailey and Hoffman, 1980; Martínez and Adame, 1987).
Omnivorous looper, green worm, or burn worm Copaxa multifenestrata Henrich Schaffer, Copaxa decrescens olivine Draudt (Lepidoptera: Saturnidae). This is a pest of secondary importance, apparently attacking only the avocado producing regions of Mexico. However, the adult is also found in Central America.
The adults are large reddish-brown butterflies from 7.3 to 10.2 cm, the males have darker tonalities and large bipectinate antennae. The females are of lighter color, with smaller antennae. The front wings have 3 or 4 circular areas with no scales, and have wavy bands of darker color.
The females lay masses of tiny eggs on the surface of the leaves. The eggs are oblong, white and measure 1.9 mm in diameter, incubating 21-22 days. The larvae go through 5 instars after hatching, varying in size, color and duration. During the fifth instar, which lasts from 7 to 9 days, they reach their maximum size, up to 6.5 cm, with yellowish green color and black spots. All instars present 3 pairs of thoracic legs. The pupae measures from 2.5 to 2.9 cm in length, they hibernate in this stage under the fallen leaves or under host trees for a period of 40 to 45 days. The total life cycle lasts from 106 to 122 days, and two generations occur per year.
This pest defoliates severely, but the damage is only considered important in young trees or in the greenhouse (Figure 38 Avocado damaged by omnivorous looper or "gusano medidor") Defoliation in adult trees is concentrated in few branches and apparently does not affect production (Bravo, et al.,1988).
Green fly Aetalion quadratum Fowler (Homoptera: Aetalionidae). The only host for this pest is the avocado tree, and fro this reason the green fly is considered monophysitic, or accentric. It prefers the native Mexican-Guatemalan ecotypes such as "Fuerte". It is found in the Mexican high plateau and in northern Guatemala.
The adults are insects that reach 1 cm in length. Their color is green to grayish brown, with some orange spots; the wings are membranous with marked venations and a little longer than the body. The eyes are red and the male is slightly smaller than the female. The females lay eggs in young branches and tender shoots where they make small incisions. The eggs are white, almost transparent, and oblong in shape, 1.4 by 0.5 mm and ordered in lines separated longitudinally as well as transversally by a waxen partition. The egg masses are oval in shape, slightly raised, 0.5 to 0.8 cm of width, and up to 1.0 to 1.5 cm in length. The female stays on top of the eggs until the nymphs emerge, which are white in color but rapidly change to a yellowish-green color, and then to a grayish color in only a few hours. They go through 5 instars, at first with semi-mobile wings. The complete life cycle can last from 129 to 140 days with two generations per year. The first adults appear in the spring (March-April) and the second generation at the end of the summer (August-September). They can hibernate as eggs or adults.
Given the fly's habits of forming numerous groups or colonies, and almost spending their lifespan on the same branch, they are able to affect many branches of a tree and kill the new shoots, causing loss of vigor and consequently diminishing the production. The mobility of the green fly is very limited, therefore their dispersion is slow, taking one generation to spread from tree to tree. A secondary damage caused by this pest is the association they often present with phytopathogenic fungi. The adults and the nymphs feed by puncturing and sucking the branches, producing injuries that secrete a white granular sap, that together with the secretions of the insects, form a favorable medium for the development of fungi, such as Glomerella singulata and Capnodium spp. This causes the withering of the branches and sooty molds, respectively (Morales, 1957).
Avocado treehoppers or avocado parakeet Metcalfiella (Hoplophorium) monogramma Germar (Homoptera: Membracidae). This was a widely distributed pest in all the native Mexican avocado zones, mainly on the Mexican high plateau. Today, due to the expansion of the cultivation of the Hass variety, this pest is no longer of importance (Bravo et al.,1988, Morales, 1957).
Avocado leaf gall Trionza anceps Tuthill (Homoptera: Psilidae). It is considered a monophysitic pest since its only reported hosts are the native Mexican avocado tree and comes times the Mexican-Guatemalan variety known as "Fuerte", and on extremely rare occasions the Hass variety. It has only been reported in the avocado zones of Mexico and Guatemala.
The adults are very small, flattened insects of oval shape, no larger than 2.5 mm, of greenish-yellow color with transparent wings longer than the body. They have strong and short legs that help them to walk and jump easily. They have long and fine antennae consisting of nine segments; red eyes and a highly developed thorax. The females lay 1 to 7 eggs in the cut they have previously made on leaves, and place them between the surface and the parenchyma tissue. The eggs are no larger than 0.25 mm, and upon hatching, the nymphs begin feeding on the tissue, secreting substances that act as stimulant to the cells, which begin to grow in a hypertrophic manner. The nymphs pass 5 to 6 instars inside the leaves, gradually increasing in size from 0.3 to 2.5 mm. They are of flat, oval shape, yellowish-orange color, and have a border of hair or quills around the edges. In the last instar, they leave the gall through an orifice in its base or in the underside of the leaf. The life cycle is estimated to last approximately 60 days, and there are 5 or 6 overlapping generations per year.
Spectacular symptoms can be seen since a large number of galls are formed. The gall is light green at first, and then turns dark green, brown or dark brown once the adults have migrated. The dimensions also vary with time, growing from 2 to 3 mm in diameter to 4 to 5 mm. In intense attacks, there is defoliation with severe consequences in production, due to the loss of both quality and quantity of the fruit. When the trees have been infested with these parasites for a number of years, they are no longer productive (Bravo et al.,1988, Morales, 1957).
Measuring worm Sabulodes aegrotata Guenee (Lepidoptera: Geometridae). Several species of the genus Sabulodes have been found in California, Mexico and Central America.
The adults are small moths of light yellow or light brown color and from 2.5 to 3 cm in length, with a wingspan of 6 to 7 cm. They have two dark stripes across the upper part of the wings. They are nocturnal in habits, resting on leaves, branches, or shady trunks during the day. Their lifespan is of approximately 20 days. The females lay 200-300 eggs in groups, being of pale green color at first, and turning brown when hatched. After 8 days of incubation, small yellowish larvae are produced that feed on the epidermis of the leaves. After a second instar, they feed on the entire leaf, leaving only the nervation. After a third instar, they reach a length of 6 cm and turn dark green with dark lateral strips along the body. After 40 days, they transform into pupae of 2.5 to 3.0 cm in length, brown in color, and locate between two leaves, or in rolled leaves. They can stay in this stage from 15 to 30 days, depending on the weather. The total life cycle varies from 2 to 3 months.
The damage of the measuring worm is very severe, since it is a pest whose incidence varies from year to year, and only in patches of few trees in an orchard. However, in some regions and in certain years, greater damage is produced, defoliating the infested trees completely and destroying the new shoots. The greatest incidence occurs during the summer (Anonymous, 1979; Gallegos, 1982).
Morales et al (2000) developed a sampling technique to determine the status of avocado pests in the state of Michoacán, Mexico. According to their method, they randomly selected 96 trees from a total of 27 ha or 2760 trees, which were divided into sections. 110 fruits were analyzed in each of the 96 selected trees. The results are shown in the table 11.
| Pest or type of damage | Number of affected fruits | Percentage % |
| Avocado blight (roña) | 749.7 | 7.1 |
| Anthracnose | 211.2 | 2.0 |
| Thrips | 475.2 | 4.5 |
| Mix of pests | 167.0 | 1.6 |
| Other insects | 64.0 | 0.6 |
| Mechanical or sunburn | 95.0 | 0.9 |
| Total damaged fruits | 1764.1 | 16.7 |
| Undamaged | 8796.0 | 83.3 |
These authors observed that the major pathogen in Michoacán are: Colletotrichum sp, that causes anthracnose (Figure 39 Avocado affected by anthracnose); Sphaceloma persea, causing avocado blight (roña); Alternaria sp, causing rot; Fusarium sp and Diplodia sp, causing black spots in the peduncle; and finally bacteria as secondary agents causing watery rot.
Figure 39 Avocado affected by anthacnose
Source: Sanidad Vegetal de Salvador Escalante Michoacán, México
Root-rot: Watering must be suspended for trees with slight symptoms, their roots exposed and the fungicide "Upritán" applied. Some farmers apply copper fungicides at high doses, however the causal agent in these cases was not fully identified. Strongly attacked trees must be uprooted and disinfected with a solution of 40% formic alcohol or commercial fungicides such as "Vapam" of methyl bromide. Ditches (50 cm wide and 50 to 100 cm deep) shall be dug around the affected trees (Morales, 2000).
Avocado blight (roña): Pruning of trees helps control the fungus because it grows better in closed orchards (Figure 40 Avocado blight). It is also important to remove the fallen and ill fruit, because they are the primary medium for the incubation of the pest. In some avocado producing regions, this disease has been controlled with applications of micronized copper (53% copper) in doses of 1 to 2 kg per 400 L of solution or using a mix of 1-1-100 lime-copper sulfate -water (Martinez, 1975) (Figure 41 Avocado trees are sprayed with lime -copper sulphate- water).
Thrips: A natural biological control exists when wasps (Desycapus pariopennis Gaham, Trichogramatidae family) parasite the thrips eggs. There are other predators such as Leptothrips, Franlinothrips, and Watsoniella. An important cultural control is the elimination of weed, and keeping the orchard clean. This is a pest easily controlled by chemical pesticides, such as malathion and parathion. For severe attacks, pyrethrines such as fluvalinates are recommended (Adame, 1994; Gallegos, 1982). Chemical pesticides should be applied when 10% and 100% of flowers appear, and when fruits are in bud stage (Téliz, 2000).
Small seed weevil: An integrated management is required in order to control the pest, including cultural labors, chemical, and legal control. Eradication is considered in most cases since this is a pest under quarantine. The cultural control consists in the destruction of infested fruits, together with soil labor to destroy the pupa. The chemical control is carried out using methylic parathion or malathion in powder (2 to 3%) applied to the soil during the emergence of adults. Aspersions with the same products in doses of 1 to 2 L / 1000 L of water every 10 days while adults are present. The legal control includes the establishment of campaigns for prevention in free zones and quarantines to avoid dispersion (Bravo et al.,1988; Llanderal de la P. and Ortega, 1990; Martínez et al.,1987).
Large seed weevil: The greatest efficiency in the control of this pest is achieved when combining chemical and cultural controls. The spraying of the foliage every 8 to 10 days after adult insects appear is recommended, using phosphate-containing chemicals such as methylic parathion, malathion and ethylic gustathion in doses of 1.0 to 2.0 L in 1000 L of water. As a cultural control, it is important not to leave fruits on the tree after the harvest, gather all the fallen fruits and destroy them. A biological control that gives 20% efficiency can be achieved with Bracon sp (Bravo et al.,1988; Gallegos, 1982).
Seed moth: A combination of chemical and cultural control is needed. The cultural control consists in pruning the affected branches, gathering the fallen fruit and burying or incinerating it. Chemical control can be used for adult insects by spraying phosphate-pesticides, carbamate, or piretroid pesticides, such as malathion, gustathion, sevin and permetrines in commercial doses. Phosphate-containing pesticide in powder form can also be applied at 2% to the soil when the fruit begins to fall of during the emergence of adults (Bravo et al.,1988; Gallegos, 1982; García-Martel et al., 1983).
Red or brown mites: There are mentions of natural control by means of predators such as Stethorus picipes Casey, Oligota oviformis Casey, O. pigmaea, Crysopa spp., Scolothrips sexmaculatus Pergande, and of several species of mites of the Typhlodromus genus. However, their control is limited and the chemical control is recommended with the use of various products such as powder of liquid sulfur, in doses of 3 to 5 g per 1000 L of water; mineral oil; Endosulfan, Abamectine (Avermectine), Metamidofos, Fluvianato, Propargite, and Ethion in commercial doses. Resistance and limited control of phosphate-containing pesticide has been reported, therefore their use has been limited in this case (Arias, 1984, Eveling, 1959, López, 1990).
White fly: due to the characteristics of this particular pest, and to the environmental conditions of high humidity and shade that they require to survive, the elimination of weeds and the pruning of trees are very useful labors for the control of white flies. For chemical control, phosphate-containing pesticides and pyrethrins are recommended (Martínez, 1984).
Dog worm or Swallow wing butterfly: A natural control is carried out with beneficial species in the different stages of their cycle. A parasite of the worm's egg (Telenomus, Scelionidae family), and a wasp parasite of the pupae (Pteromalidae Pteromalus) are of importance in Mexican cultivars. The release of Trichogramma minutum is also very efficient. The chemical control is almost never required, except in particular cases when the infected trees are sprayed with pyrethrines or carbamates in commercial doses (Bravo, 1988; Del Rio, 1978).
Leaf roller worm and Amorbia moth: Like other Lepidopters, they can be severely attacked by natural enemies in their different stages. The eggs are attacked by Trichogramma platneri in California, and T. minutum in Mexico. Spraying with Bacillus thruringinesis in commercial doses is also helpful. Pyrethrins and carbamates in commercial doses are used occasionally when severe infestations occur (Bailey, and Hoffman, 1980; Martínez, and Adame, 1987).
Omnivorous looper, green worm, or burn worm: The larvae are controlled naturally by the Ichneumonidae wasp parasite Enicospilus. The pest can also be chemically controlled by spraying only the affected trees with a mix of carbamates, phosphate-containing pesticides, or pyrethrins in commercial doses (Bravo et al.,1988).
Green fly: It is very susceptible to pesticides, and can be controlled in the nymphal stage as well as in the adult stage. Given their low mobility, they are easy to control with products such as malathion ot parathion, sprayed on the foliage in doses of 100 to 200 mL/100 L of water (Morales, 1957).
Avocado treehoppers or avocado parakeet: The exchange of the Mexican avocado varieties for Hass, eliminates the presence of this pest in commercial orchards. Native trees can be sprayed with parathion or malathion in commercial doses (Bravo, et al.,1988, Morales, 1957).
Avocado leaf gall: Its natural enemies are unknown. This pest is very resistant to climatic conditions such as cold or rain. Furthermore, in the nymph stage (inside the gall) it is very resistant to pesticides. However, the adults can be easily controlled when coming in contact with parathion and malathion in commercial doses (Bravo et al.,1988, Morales, 1957).
Measuring worm: The environmental conditions, as well as natural enemies, control the pest. It is often found that virus, bacteria, and wasps (Apanteles, Bracon, Zele and Meteorus) also attack the larvae, Trichogramma and Telenomus parasites attack the eggs, and flies of the Tachinidae family attack the pupae. Commercial applications of the Bacillus thuringiensis entomotoxin and releases of Trichogramma minutum produce excellent results. The application of chemicals is almost never required, but if necessary, should be applied only to a few isolated trees. Pesticides containing phosphates are only efficient in high doses, therefore permetrines or carbamides are recommended in commercial doses (Bravo et al.,1988, Morales, 1957).
In order to establish a good strategy for integral pest control, thresholds and levels of economical damage need to be determined. This can help to reduce the frequency of fumigations, lower the crop handling costs, as well as to increase the production. The study of beneficial fauna can lead to the development of biological controls (Téliz, 2000).
In Mexico, only four pesticide products are recommended for chemical control: 1) parafinic petroleum oil (Saf-T-Side), 2) Malathion CE 47; 3) Methylic parathion (Folidol) CE 47, and 4) Permetrine CE 49 (Téliz, 2000).
In Chile, the presence of a large fauna of biological controllers has helped to contain potential avocado pests. However, there is no doubt that the use of pesticides in the orchards contribute to maintain this situation. Different pests that sometimes need to be restrained can be handled with selective pesticides that do not interfere significantly with biological controllers. In other cases, the spraying specific sectors of the orchard helps to maintain the beneficial fauna.
In the same way, the establishments of reservoirs for biological controllers,
together with cultural practices such as the elimination of low branches, removal
of branches that constitute the origin of infections, and the maintenance of
vegetation that feed beneficial fauna in adult stage, are also biological control
practices. Finally, the artificial introduction of biological controls through
a development and release method can help solve those situations in which the
beneficial fauna is not efficient enough or does not colonize the orchard on
time (López-Laport, 1999).