Washington State University Cooperative Extension

Areawide IPM Update

The Newsletter of Pheromone-based Orchard Pest Management

Vol. 2, No. 3 -- March 1, 1997

Cooperating agencies: Washington State University, Oregon State University, University of California, U.S. Department of Agriculture, and Chelan County.

Cooperative Extension programs and employment are available to all without discrimination.

Biological control of codling moth

One of several benefits desired by those using mating disruption for codling moth control is an improvement in biological control of many orchard pests. Reducing or eliminating the use of broad spectrum insecticides can and has permitted natural enemies to better control a number of pests, including leafrollers, leafminers, aphids and pear psylla. Codling moth (CM), however, has very few natural enemies in the Western U.S., and fruit infestation by CM can easily exceed 90% in untreated trees. The codling moth is thought to have originated in Central Asia, the ancestral home of the apple. Kazakhstan has forested mountains where apples are the dominant tree species. In that region, more than a dozen CM parasitoids have been identified. Parasitism of CM can exceed 60% there, with fruit damage as low as 20%, even in warm areas with three full CM generations. When CM came to North America it left this complement of parasitoids behind. Native North American parasites generally provide less than 5% parasitism in unsprayed situations.

Efforts have been underway for many years to introduce and establish several types of CM parasites in North America. It is not expected that these parasites can alone provide sufficient CM control for commercial apple producers. Rather, their successful establishment could reduce the threat coming from abandoned and neglected apple blocks and help reduce CM population pressure on a regional basis, perhaps further reducing the need for supplemental chemical controls in a pheromone-based pest management program.

Dr. Tom Unruh of the USDA-ARS Entomology Lab in Wapato, WA, has made several excursions to Europe and Central Asia in search of CM parasitoids, most recently in September of 1996. He has successfully reared and released a number of parasitoids in Central Washington orchards. His efforts in 1996 focused on two that attack cocooned larvae, the overwintering stage of CM.

Two wasps originally from Eurasia, Liotryphon caudatus and Mastrus ridibundus, have been reared in his lab on diapausing CM larvae. Releases of females of both species were made in a number of organically managed or insecticide-free orchards between September 4 and October 16, 1996. The results were highly variable. Up to 60% parasitism was obtained with the earlier release timing, with most of this provided by Mastrus. Later releases provided 10% parasitism or less. These results indicate the need to make releases early enough to allow enough warm days for the parasitoids to find and parasitize the larvae. Both wasps are very good at searching out and locating the scattered and well-hidden CM larvae. In addition, they are highly mobile, providing a high degree of parasitism in blocks well removed from the release site.

In 1997, Dr. Unruh will make releases targeted at both the summer and fall CM generations, with the intent of both augmenting the CM control provided by mating disruption and possibly establishing a permanent population of the parasites. These trials will emphasize Mastrus because this gregarious species can be reared more economically than the solitary Liotryphon species.

Spiders in apple orchards

Spiders are among the most common and abundant arthropods found in many habitats, including orchards. All spiders are predators, mostly of other arthropods including a vast array of insects. Despite their abundance, relatively little is known about what role they play in orchard pest control. Spider numbers have been noted to increase in orchards where broad spectrum insecticide use has been reduced. Their impact on pest control has generally been regarded as positive except, perhaps, by those who have just walked full face into an orb spider's web!

Drs. Gene Miliczky and Carrol Calkins in 1996 began an investigation of spiders in apple orchards. Their studies focused on determining the seasonal abundance and diversity of spiders under three pest management regimes: conventional insecticide use, reduced insecticide use (the West Parker Heights CAMP site), and organically-approved insecticide use. Weekly samples were taken from early June on, using beating trays to sample tree foliage and sweep nets to sample the ground cover vegetation.

Beating tray samples show some clear differences between the different pest management systems. Spiders were least abundant in the conventional orchards, averaging close to 4 per sample and declining in number from June on. Spiders were considerably more numerous in the CAMP orchards, with means ranging from 8 to 20 per sample through the season. Populations were highest in the organic blocks sampled, with mean numbers per sample varying from 17 to 43. These organic blocks had considerably higher arthropod numbers in general, providing more food for spiders.

The diversity of spider families represented also increased as the spider populations increased. The predominant families included the Salticidae (jumping spiders), Oxyopidae (lynx spiders), Thomisidae (crab spiders), Philodromidae, Linphyiidae (sheet-web spiders) and Theridiidae (comb-footed spiders). The first four are hunting spiders that pursue or grab their prey and have no web or substantial shelter. The linphyiids and theridiids are web makers and were relatively more abundant in conventional orchards. The sample method used (beating tray) biases collection towards the more mobile spiders, and tends to under-represent those that are well-webbed or primarily nocturnal. Sweep net sample results are still being analyzed.

Further investigations are planned for 1997. The sampling program will be expanded, beginning earlier in the season (March) and including additional sampling methods. The webs of some common web-spinning spiders will be examined to determine their prey through the season, and feeding tests will be conducted with some of the more abundant spider species to see whether they will feed upon apple pests, such as leafhoppers and leafminers.

Botanical insecticides

by Dave Kain

Naturally occurring pesticides that are derived from plants or plant parts are commonly referred to as "botanicals." Botanicals have been around for quite a while. Along with arsenicals and other inorganic pesticides, they were commonly used before the advent of synthetic organic pesticides rendered them obsolete. From time to time they're re-examined for various reasons and may be familiar. Botanicals are of interest to those concerned with pest management for a variety of reasons. They are generally less toxic to the applicator than many synthetic insecticides. They may be acceptable in the organic market where synthetic pesticides are not. They generally break down quickly, so they may also be of use near harvest when control is needed but other materials may not be applied because of PHI restrictions. Rapid degradation also means they are less likely to become environmental problems. Botanicals, however, are not without concerns. They are usually broad-spectrum poisons that can be hard on beneficial insects. And, unlike "biological pesticides" like insect growth regulators and pheromones, they are acutely toxic to humans and other animals. The fact that they break down rapidly in the environment, while an advantage in some respects, also means that sprays need to be:

They are also very expensive.

The four most common botanicals available for use in fruit crops today are rotenone, pyrethrin, sabadilla and ryania. A relatively new and increasingly used botanical insecticide that is receiving more attention these days is azadirachtin (or neem).

Rotenone is derived from the root of various plants of the genus Derris or Lonchocarpus from Southeast Asia, Central or South America. It is available as at least 118 formulated products from a large number of manufacturers. It is synergized by the addition of piperonyl butoxide (PBO), which is another botanical material. Rotenone is expensive when compared with synthetic pesticides, but is moderately priced for a botanical. It is the most commonly mentioned of the botanicals in pre-synthetic literature and is at least somewhat effective against a large number of insect pests. These include: pear psylla, cherry fruit fly, apple maggot, pea aphid (which is similar to rosy apple aphid), European red mite, two-spotted spider mite, codling moth, plum curculio and tarnished plant bug. Unfortunately, it is also toxic to ladybird beetles and predatory mites. It is non-toxic to syrphid flies (aphid predators) and honeybees. Rotenone is rapidly degraded by sunlight, lasting a week or less.

Of the botanicals covered here, rotenone is the most toxic to humans and other mammals. The acute oral LD50 is from 60-1500 mg/kg. In small doses it may be irritating or numbing to mucous membranes. It is highly toxic to fish, having been commonly used as a fish poison. It is also toxic to birds and pigs.

A recent regulatory development illustrates the tenuous situation of many minor-use materials and may render the preceding discussion academic before long. According to a USDA news release, the Rotenone Task Force has announced that it plans to delete all agricultural uses from rotenone labels because of the cost of re-registration. The registrants plan to maintain rotenone uses for fish control and flea/tick/mite control on dogs and cats.

Pyrethrin (pyrethrum) is a compound produced in the flowers of Chrysanthemum cinerariaefolium and is the forerunner of the synthetic pyrethroid insecticides. There are not nearly as many commercially available formulations of this chemical as there are for rotenone. It is available from several sources as an emulsifiable concentrate, in a combination with rotenone, or alone as a wettable powder. Pyrethrin is the least expensive of the botanicals reviewed here. Depending on the rate, it may be less expensive than many synthetic pesticides. It is also synergized by PBO. Pyrethrin is labeled for use against a large number of orchard pests. An addendum to the label for one formulation showed it to be moderately to highly effective (61-100% control) against the following pests: grape leafhopper, leaf curl plum aphid, blueberry flea beetle, blueberry thrips and blueberry sawfly. It is quickly broken down in the environment and may be used up to and including the day of harvest. Pyrethrin is relatively non-toxic to humans and other mammals, although the dust produces allergy attacks in people who are allergic to ragweed pollen. The acute oral LD50 is 1200-1500 mg/kg. It is toxic to fish, but relatively non-toxic to honeybees.

Sabadilla is derived from the seed of a tropical lily. There are very few commercial formulations of this material. It is available as a dust that may also be added to water and sprayed, but clogging of the nozzles has been noted. It is moderately priced for a botanical (similar to rotenone). It will control potato leafhopper and is somewhat effective against tarnished plant bug. It has little effect on predators/parasitoids but a recent test showed it to be quite toxic to the predatory mite Typhlodromus pyri.

Sabadilla may be used up to 24 hours before harvest. Apple is the only deciduous tree fruit crop specifically mentioned on the label of the one product we found registered for New York use. Information from several sources has been ambiguous about toxicity to honeybees. Some say it is relatively non-toxic to honeybees, and others (including the manufacturer) say it is toxic. The confusion may lie in the fact that sabadilla is toxic to honeybees on contact, but without any residual activity. In the interest of playing it safe (especially given the current state of honeybee health), it would be best to consider sabadilla a hazard to honeybees and to follow all necessary precautions to prevent their exposure to the material. Sabadilla is less toxic to mammals than rotenone or pyrethrin: the acute oral LD50 is greater than 4000 mg/kg.

Ryania is a product from the roots and stems of Ryania speciosa, found on the island of Trinidad. Ryania acts as both a contact and stomach poison on target insects. It is the most expensive of the materials covered in this article, and is less readily available than rotenone or pyrethrin. Ryanodine, the active ingredient, is formulated as a wettable powder and is labeled for use against codling moth on apples. In Joe Kovach's tests in New York it provided excellent control of a pest complex comprised of codling moth, oriental fruit moth and lesser appleworm. It also controlled aphids, white apple leafhopper and spotted tentiform leafminer. It is more persistent than rotenone or pyrethrin and is more selective. It is generally not very harmful to predators and parasites, but is somewhat toxic to the predatory bugs Atractotomus mali and Diaphnocoris spp. It may be used up to 24 hours before harvest. The acute mammalian oral LD50 of ryania is 750- 1200 mg/kg, making it less toxic than rotenone and slightly more than pyrethrin. It is also toxic to fish.

Azadirachtin (neem) is derived from the seeds of the neem tree, Azadirachta indica, which is widely distributed throughout Asia and Africa. The observation that the desert locust did not eat the leaves of the neem tree and another closely related species led to the isolation and identification of azadirachtin in 1967. Since then, azadirachtin has been shown to have repellent, antifeedant and/or growth-regulating insecticidal activity against a large number of insect species and some mites. It has been reported to act as a repellent to nematodes. Neem extracts have been used in medicines, soap, toothpaste and cosmetics.

The most common commercial formulations available for N.Y. tree fruit are Neemix, which lists leafminers, mealybugs, aphids, fruit flies, caterpillars and psylla on the label, and Align, which includes some leafrollers on the label. Azadirachtin has shown good activity against spotted tentiform leafminer in tests in past years, but the formulation available at the time was somewhat phytotoxic. In Dick Straub's insecticide trials in 1992 with another azadirachtin product, called Margosan-O, the insecticide showed good activity against STLM and leafhopper. Margosan-O is no longer available for fruit crops. In laboratory tests by Jan Nyrop's lab, toxicity to the predatory mite Amblyseius fallacis was very low. Field trials by Harvey Reissig in 1995 were not encouraging. Azadirachtin is relatively short-lived and mammalian toxicity is very low (rat oral LD50 >10,000). It can be used up to and including the day of harvest. It is toxic to fish and aquatic invertebrates.

Piperonyl butoxide (PBO) is a synergist, a material that when added to a pesticide increases the activity of the active ingredient. It is used with both rotenone and pyrethrin. It is also a botanical product, being derived from Brazilian sassafras. it is very safe, having an acute oral LD50 of greater than 7,500 mg/kg, but it may be chronically toxic in high doses.

Dave Kain is employed by the New York State Agricultural Experiment Station in Geneva, New York. This article first appeared in the July 29, 1996, issue of Scaffolds Fruit Journal, a weekly publication on tree fruit insect and disease management put out during the growing season by the NYSAES. It is available on the WWW at www.nysaes.cornell.edu/ent/scaffolds.

Ted Alway, Editor
Phone: (509) 664-5540
Fax: (509) 664-5561
e-mail: alway@coopext.cahe.wsu.edu

Partial Funding provided by: Washington State Tree Fruit Research Commission, U.S. Department of Agriculture-Agricultural Research Service.

WSU Cooperative Extension, Chelan County
400 Washington St.
Wenatchee, WA 98801

Wenatchee WA, 13 March 1997