Biocontrol Solutions for Avocados
PO Box 1555, Ventura, CA 93002
800-248-2847 * 805-643-5407 * fax 805-643-6267
At Rincon-Vitova Insectaries, we help our customers use beneficial insects and predatory mites for sustainable natural biological pest control. We typically advise using either no pesticides, or where intolerable crop damage is likely, an integrated pest management [IPM] strategy of spraying the lowest possible rates of least toxic pest control compounds like soaps, oils, botanicals, microbials and high pressure water sprays.
This low-input natural biological pest control strategy allows pest-eating beneficial insects, predatory mites and spiders to survive, reproduce and increase their populations in orchards. Over the course of two to three seasons, a combination of purchased beneficials from Rincon-Vitova Insectaries and sustainable farming practices [e.g. cover crops; natural enemy refuge strips; IPM] can tip the long-term orchard ecological balance from pest outbreaks to the establishment of beneficial species and natural biological pest control.
Avocado pest control has become more complicated in recent years with invasions of caterpillars like the Amorbia leafroller and loopers, along with greenhouse thrips and persea mite. Nonetheless, some of Rincon-Vitova Insectaries' oldest avocado customers have conquered these pests with biological control, spraying nothing harder than micronutrients in the last 25 years. Hence, we know from many years experience that avocado orchards can be inoculated with beneficial insects, predatory mites and decollate snails [brown garden snail predators] and farmed sustainably for decades with minimal or no pesticides. The key is farming in a way that builds up a large reservoir of natural enemies that act as a buffer, absorbing invading pest populations.
Spraying avocado trees with even the least toxic pesticides, likes soaps, oils, microbials [e.g. BT], botanicals and sulfur, can be an expensive affair, whether with ground rigs or helicopters for optimum spray coverage of leaf undersides. Hence, any pesticide sprays replaced by an arsenal of orchard-grown beneficials fattening themselves on pests means more dollars staying at home in the orchard profit column.
Indeed, Rincon-Vitova's most successful customers have developed such a rich assemblage of beneficial natural enemy species in their orchards over the years that even beneficial insect purchases have become fewer and far between. Once orchards are successfully inoculated with new beneficial species and farming practices modified to grow large quantities of predators and parasites in the orchard, beneficial insect purchases are typically needed only for new pest species [e.g. persea mite] or an ecological upset like a severe cold spell or pesticide spray drift killing the beneficials.
When a new pest species, such as persea mite, becomes common in an area, inoculating orchards with new natural enemy species, such as Galandromus predatory mites or six-spotted thrips, is a sensible step in conjunction with an IPM strategy that nurtures and encourages growth of the new beneficials. Rincon-Vitova's beneficial insect and predatory mite products help create an orchard ecological balance where beneficials eat enough pests to prevent major problems.
Low levels of pests causing little economic loss are tolerated as food for the beneficials. Indeed, farming practices may even be altered to be more sustainable, with more mulches, cover crops and special "insectary" plants to grow more pest controlling beneficial insects in the orchard.
Once inoculation of new natural enemies is successful and farming practices are such that large quantities of diverse beneficial insects are being grown on the farm, the need for purchasing pest control inputs of all types diminishes. About the only pest control operation that we automatically recommend year in and year out is regular monitoring of the orchards, preferably with a knowledgeable consultant or PCA, to keep on top of potential pest problems and detect new pest species.
Persea Mite Biocontrol
Persea mites, Olygonichus persea, are small yellowish spider mites living in colonies and spinning very fine silvery or whitish webbing along veins on the undersides of leaves. The top sides of infested leaves have yellow spots that later die and turn brown from mite feeding. If persea mite populations explode to over several hundred per leaf, defoliation and sunburning of fruit are a threat.
Typically, persea mite populations peak in summer and decline during hot spells [100 F, particularly when humidity is low] and cooler weather. But unless biological controls like green lacewings, six-spotted thrips and Galandromus predatory mites sold by Rincon-Vitova become established, persea mites will stage a comeback in the spring.
The best IPM remedy for persea mite is high pressure water sprays, as these are least toxic to the beneficials providing biological pest control. Indeed, persea mite predators like Galandromus can be released immediately after high pressure water sprays, as there is no toxic residue on the leaves to kill the predators. Work on remedies like oils, sulfur and botanicals is continuing, and Rincon-Vitova Insectaries will be happy to share with callers the latest IPM tactics as information becomes available.
Predators sold by Rincon-Vitova Insectaries that can be added to the natural enemy complex fighting persea mite include the predatory mites Galandromus helveolus and Galandromus annectens, six-spotted thrips, and green lacewings, Chrysoperla species.
Galandromus species are an excellent choice for avocados, as these predatory mites reproduce relatively fast in unsprayed orchards, with a new generation of predators every one to two weeks. These predators eat every life stage of persea mite from egg to adult. Each Galandromus female lays two to three dozen eggs during its one month life span. Both G. helveolus and G. annectens are able to penetrate the dense white webbing in which persea mites hide even more effectively than pesticides. Penetrating this webbing is difficult for many of the native predatory mites currently found in avocado orchards.
Galandromus helveolus survives on other pests, such avocado brown mite and six spotted mite, when there is no persea mite, making it an especially good addition to orchards. Also, G. helveolus can help with biological control on other crops, including citrus and grapes.
G. annectens survives on pollen when persea mite is scarce, but needs to eat mites to reproduce. G. helveolus reproduces faster. But G. annectens overwinters better, survive temperature extremes better and survives better when persea mite numbers are low.
Recommended release rates for Galandromus species are a minimum of 100 per tree or 5,000 per acre, beginning when persea mite activity is first noted. Releases may continue into a second or third season to ensure establishment over the whole orchard. Galandromus spread very slowly, taking three months just to colonize one tree in which they are released. It can take over six months for Galandromus to spread to neighboring trees.
Thus, for quickest predatory mite colonization of trees, make sure that each tree is individually inoculated by releasing Galandromus directly onto avocado leaves infested with persea mite. Your PCA, consultant or Rincon-Vitova Insectaries can supply more details on the best release techniques for Galandromus. Predator release technology is continually improving as we learn more about mite ecology.
After Galandromus are released, practice IPM to avoid pesticide kills and having to start over with releases. Also, be aware that residues from previous sprays are harmful to Galandromus. If pesticides have been used or are contemplated, Rincon-Vitova will be happy to share the latest information we have on waiting periods for residues to disappear before making predator releases for peresea mite and on predator reactions to various hard and soft pesticides.
Rincon-Vitova Insectaries recommends high pressure water, rather than pesticides, whenever possible, to knockdown persea mite numbers before releasing predators. It takes only 45 seconds in water for persea mites to drown, and in their native Mexico summer rains naturally reduce persea mite populations. In contrast to persea mite's poor survival in water, some predatory mites are known to survive in water by floating, though we have not yet tested Galandromus survival in water.
In general, predatory mites are rather mysterious, with only a handful of species even being known to science prior to the 1950s. Predatory mites can be particularly difficult to monitor and detect, particularly in tall trees like mature avocados, where sampling is generally limited to those few leaves within arm's reach. Thus, months can go by in which biological control may be working undetected on leaves not easily sampled.
Avocado is native to rainforests, and rainforest trees are noted for complex insect ecologies. Indeed, in rainforests different insect species may live at different heights within the tree canopy. Thus, a ground level person may only be able to detect a small percentage of the insect species actually living in the tree. Complicating sampling and monitoring even more, predatory mites are very mobile and hard to detect. Mites and predators can move between tops, middles and bottoms of trees, as well between exterior and interior leaves, and on cycles that can be daily [e.g. AM/PM], weekly, monthly and seasonal.
Sometimes predatory mites survive at very low population levels, almost undetectable, for long periods of time before suddenly exploding in massive numbers and providing biological control. Very few scientists study predatory mites, so the reasons for this are poorly understood. Thus, unlike pesticides, where results may be clear and immediate, growers releasing predatory mites may not get full feedback on successful establishment for several months or two to three seasons. This period of uncertainty during the transition and initial establishment of biological control is, psychologically, the most difficult period.
Other Avocado Pests & Natural Enemies
Green lacewing larvae are generalist predators, consuming greenhouse thrips, aphids, small caterpillars and other orchard pests besides persea mite. Lacewing release methods and numbers vary from orchard to orchard, depending upon terrain and other factors, and are best planned individually by talking directly with Rincon-Vitova Insectaries, a consultant or PCA.
There are many intricacies in releasing lacewings, and Rincon-Vitova's lacewing technical bulletin is recommended reading. It is wise to map out orchard ant activity, as ants eat lacewing eggs. Thus, for some areas of the orchard, lacewing larvae might be released rather than lacewing eggs to avoid ants; and ant control measures might be used.
In general, lacewing recommended release rates are 10-15 hatching eggs or 2-10 larvae per tree. The decision whether to spray on lacewings or hand place lacewing egg cards in trees is also best discussed on a case by case basis with Rincon-Vitova Insectaries, a PCA or consultant.
Even when mite populations are high in orchards, it is a good idea to have a consultant or independent PCA check for natural enemies, viruses and other pathogens. Often, high mite populations are wiped out by natural enemies like little black Stethorus lady beetles, which mostly migrate into orchards with high mite populations. Under certain weather conditions, high populations of mites succumb to viruses that make them listless and stop feeding before the high populations suddenly crash to near zero. Thus, monitoring by a trained invididual can save a pesticide spray and spare natural enemies like minute pirate bugs, big-eyed bugs, six-spotted thrips [also sold commercially by Rincon-Vitova Insectaries], midge larvae and an array of native predatory mites. These beneficials and their progeny can then live to provide many more seasons of free natural biological control as part of the ecological natural enemy reservoir that builds up in unsprayed orchards.
It would cost thousands of dollars, and be economically prohibitive to purchase the quantities of natural enemies building up on high mite populations. So, bringing in a professional for IPM advice during the crucial decision points can be a profitable investment.
Rincon-Vitova Insectaries also raises a caterpillar/moth egg parasite, Trichogramma platneri, which destroys eggs of Amorbia, the avocado leafroller, and omnivorous looper, Sabulodes aegrotata. T. platneri is not meant to be a standalone remedy. Rather, T. platneri supplements existing natural enemies. As populations of T. platneri and other natural enemies, especially spiders, increase during the season, the need for pesticides is eliminated in many orchards.
Rincon-Vitova recommends releasing between 50,000 and 200,000 Trichogramma platneri per acre over a several week period beginning with the first spring flights of Amorbia and looper moths. A PCA or consultant can help with monitoring moth flights and ordering the appropriate number of T. platneri for timely arrival each week coinciding with moth egg laying. Rincon-Vitova can also provide assistance developing T. platneri release strategies.
A few leaves chewed by Amorbia and loopers are not to be feared, as small populations of these pests are life-sustaining food items to beneficial insects providing natural biological pest control. Ideally, T. platneri,
green lacewings and other natural enemies will provide the extra percentage of pest control needed to augment existing orchard natural enemies and keep pest populations below economic injury levels without pesticides and the pesticide treadmill effect [which comes about when sprays kill natural enemies, unleashing pests from biological control, and triggering the need for more sprays].
Unsprayed orchards can grow populations of Tachinid flies, which along with wasp parasites of caterpillars, such as Telenomous species, have been known to kill 70% of looper caterpillars. Add in some pest kill by Trichogramma platneri, green lacewings and other natural enemies, and biological control can be substantial enough to eliminate the need for sprays.
Greenhouse thrips, Heliothrips haemorrhoidalis, are a problem in some orchards, particularly after mild winters. Thrips are controlled by a range of predators, including green lacewings. Since there are not native thrips parasites in most orchards, Rincon-Vitova has been distributing Thripobius semileuteus, a tiny wasp parasite of greenhouse thrips. By expanding orchard natural enemy biodiversity, Thripobius semileuteus should help shift the orchard ecological balance from pests to beneficials.
Sustainability & Ecology
Orchard ecology is complex, and Rincon-Vitova recommends sustainable farming practices that favor beneficial insects building up their numbers in orchards. For example, since thrips pupate in the soil, soil building measures that promote biological life in the soil result in more predators and pathogens attacking thrips before they emerge from the soil. Thus, building a living soil with compost, mulches and cover crops means fewer thrips surviving in the soil and flying into the trees.
The same soil building measures, such as composts, calcium and mulches, that help against thrips may also help reduce Phytophthora root rot. Being a rainforest native, avocado is accustomed to soils with 20% organic matter in its natural habitat. One of the most successful avocado growers we know at Rincon-Vitova has a thick mulch of fallen leaves, much like that found on the rainforest floor, and rich healthy white feeder roots growing just beneath the mulch surface. The biological control in the trees and on the ground is similarly impressive, ranging from rarely seen native predatory mites to decollate snails and an abundance of caterpillar-eating spiders.
Most years, this harmonious natural ecological balance and large reservoir of natural enemies, which has not been sprayed in 25 years, does not even need supplementation with additional natural enemies. But that first year of not spraying 25 years ago was the toughest by far, as the pest mite population was very high. The grower gritted his teeth and listened to the PCA, who said that the mites were infected with a virus commonly found when mite populations get high and the weather a bit humid. Though hard tobelieve, the faith in the PCA proved accurate, and the only sprays in the last 25 years have been micronutrients.
No one can promise similar results overnight, much less the first season. But getting through the tough early transition years on the path to sustainable biological control is best done with support networks, like those provided by working with Rincon-Vitova Insectaries, PCAs, consultants and other growers who have already made the transition.
A Few Final Biocontrol Tips
Besides building soils and not spraying, there are a variety of ways that the orchard habitat can be made more hospitable for natural enemy growth and reproduction. Ants sometimes "farm" pests like aphids, mealybugs and other honeydew insects. Black sooty mold growing on honeydew on the leaves and trails of ants going up tree trunks tend to be a problem more near dusty roads and orchard edges. Ant control -- e.g. with registered baits; high pressure water sprays to wash off pests sustaining the ants; disking ant nests in the soil to check colony growth -- helps natural enemies control pests by eliminating ant interference.
Providing food for natural enemies is another strategy promoting sustainable biological pest control. Flowering plants provide shade, dew, pollen, nectar and alternate insect prey to beneficials capable of moving into trees and providing biological pest control. In general, green lacewings like blooming borders, particularly sunflowers. Experiments on the best "insectary plants" for growing beneficial insects are continuing, and there is no one plant or group of plants that can be recommended for the whole state, any more than one crop variety can be recommended for all regions. Also, ways of managing insectary and cover crops and border and pest break strips to grow more beneficials are continually evolving. For example, some growers cut strips of insectary crops periodically to force beneficials out into the trees. Rincon-Vitova will be happy to share the latest knowledge on insectary crop selection and management with callers.
Finally, keep in mind that avocados are used to the abundant moisture of their native rainforest habitat when managing the crop. Plants are already stressed by low organic matter in most California soils. So, make sure that plants are properly fertilized and irrigated to better withstand insect and mite populations, as well as root rot. Adequate moisture and fertilizer also help avocado trees outgrow summer pest damage.
Ask about Rincon-Vitova Insectaries, Inc. Technical Bulletins, such as:
Tricks for Releasing Trichogramma
Backpack Biocontrol Applicator