|Vol. 3, No. 8||August 1, 1998|
Inside this issue:
Web links:...Ted Alway's Areawide IPM page ...USDA Yakima Areawide IPM page (with CAMP site descriptions) ...WSU-TFREC Entomology home page ...Index to Areawide IPM Update newsletters
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.
A Call for New CAMP Site Proposals
To qualify, proposed sites must:
In addition, sites will be favored that have a strong likelihood of continuing the areawide control approach for more than the one year for which funding is provided by the USDA-ARS. Sites will also be preferred from areas where experience with mating disruption for codling moth control is limited and where mostly small to mid-sized growers are involved (less than 100 acres each).
For more information, call Dr. Calkins at (509) 454-6570, or Ted Alway, WSU Cooperative Extension, Wenatchee, (509) 664-5540.
Pear growers have used codling moth mating disruption to a far lesser extent than have apple growers. Most pear orchards have lower codling moth pressure than apple orchards in the same area, as pear fruit is more difficult for codling moth larvae to infest. Lower pressure means fewer cover sprays and less opportunity to reduce codling moth control costs by including mating disruption in the program. Codling moth is not even the principal pest that most pear growers face in Washington. Pear psylla, spider mites and rust mites and, for an increasing number of north central Washington growers, grape mealybug are the main concerns. Most pear growers are spending $400 to $600 annually per acre for pest control, most of it aimed at these few pests.
If a softer approach to pear pest management is to be widely adopted then such a program must reduce the control costs for psylla, mites and/or mealybug AND provide consistent biological control without significant risk of fruit damage. Many growers may be making big changes in their pear pest management programs within a few years, if the Food Quality Protection Act results in the loss of organophosphate and carbamate insecticides and new, more selective insecticides are registered. What is known about biological control opportunities for Washington pear pests?
Considerable research has taken place around the world and in the Pacific Northwest looking into biological control of pear pests, with both encouraging results and limited success. Often, successful control in one area has been difficult to duplicate in other areas. Success is also limited because several of these pests (pear psylla, pear rust mite and grape mealybug) directly damage the fruit. Because of this it is often not possible to tolerate pest populations that are high enough to attract and sustain their natural enemies. Let's consider each of the principal pests separately.
|Pear psylla is the main pest for most Washington pear growers, the one around which pest control programs revolve. Feeding on foliage by nymphs and adults devigorates trees. More importantly, the honeydew psylla produce marks the fruit. The pesticides used for psylla control include abamectin (Agrimek), amitraz (Mitac), pyriproxifen (Knack), pyridaben (Pyramite) and imidacloprid (Provado), with growers typically applying two or three of these materials per year at a cost of $200-$300/acre or more.
Many insects have been found to prey upon pear psylla in the Northwest. Among the more effective generalist predators are a number of predatory bugs, including Deraeocoris, campylomma and several anthocorid species, as well as lacewing larvae and coccinellid (ladybird) beetles. Earwigs have been shown to be a good psylla predator; with their nocturnal habits they often escape detection. Even vespid wasps (yellow jackets) can feed on and reduce psylla populations (although they can be a problem come harvest time!). There are a few species of encyrtid wasps that parasitize pear psylla. One species, Trechnites insidiosus, has provided up to 70% parasitism in unsprayed orchards. Natural enemies can readily colonize pear orchards in many locations and provide adequate pear psylla control. Unsprayed orchards typically do not develop damaging psylla populations. However, psylla natural enemies are often killed by the broad spectrum insecticides used for the control of codling moth, mealybug, psylla or other pests. The challenge for many growers is to preserve the psylla natural enemies without suffering damage from other pests.
The pest control experiences of British Columbia pear growers are of increasing relevance to their Washington neighbors. The BC growers are producing primarily Anjou pears, probably the most susceptible variety to psylla damage, and Bartlett pears. They faced devastating damage to their pear crop in the late 1980's as pear psylla became resistant to the pyrethroids and mancozeb sprays used for control. By 1989 most pear orchards suffered severe defoliation and fruit damage, to the extent that in many blocks the fruit was not even harvested. Insecticides that Washington growers were using, particularly amitraz and abamectin, were not available to BC growers. Growers began to remove their pear blocks and the future looked bleak.
However, observations in organic pear orchards in the province showed that psylla were rarely a problem due to natural enemies. Linda Edwards, of Integrated Crop Management Inc., working together with the area's pear growers and federal and provincial entomologists , set about developing a pear pest management program that could use the biological control available without leaving the crop open to damage from other pests, particularly codling moth, leafrollers and mites. Pear growers had little alternative if they were to continue farming.
The use of insecticides (Guthion, diazinon, Carzol and pyrethroids) found to be hardest on the psylla natural enemies was eliminated or greatly reduced. Thiodan and Imidan, both somewhat less toxic to the true bug predators, were included in the program, as well as some other less disruptive materials. Many growers had to apply high-volume sprays of a detergent to their trees in the later summer to remove honeydew from the leaves and fruit. Within two seasons most growers had established effective biological control of psylla, resulting in not only cleaner crops but also less expense. Both amitraz and abamectin are now registered for use by BC growers, but most growers either don't use them or use abamectin only at a low rate for mite control.
Washington growers have had similar experiences, although not as widespread. In the Codling Moth Areawide Management Program site at West Parker Heights in the Yakima Valley there are 85 acres of pears now in their fourth year using codling moth mating disruption. Brad Higbee, with the USDA-ARS lab near Parker, has shown that in these blocks psylla populations remain lower throughout the season than in nearby blocks using cover sprays for codling moth control, and some reduction in psylla control costs has occurred. In particular, psylla numbers do not increase greatly in the late summer and fall in the mating disruption blocks as they do in the conventional blocks, and psylla begin the following season at lower levels. Several consultants in the Wenatchee and Yakima Valleys have made the same observation. Where materials like Guthion, Penncap-M, diazinon or other broad spectrum insecticides are not applied post-bloom, either due to very low codling moth populations, the use of mating disruption, foliar oils or other soft controls, psylla predators may keep psylla numbers from building later in the summer, possibly saving a late psyllicide application.
It is important for successful psylla biocontrol that the complex of natural enemies begin their work early in the season and continue through the summer into the fall. Predators that overwinter nearby as mobile adults can be needed to get biocontrol underway by bloom. Psylla reproduce rapidly and if the predators and parasites arrive too late they can fail to keep the psylla below damaging levels. One early season spray that kills natural enemies can stop effective biological control for the season.
Biological control can depend upon their being a nearby reservoir of natural enemies. Observations in pear orchards in British Columbia, Oregon and Washington show that orchards close by native habitats can build psylla predator populations more easily than those in the midst of a large orchard area, although these latter orchards have also had success with biocontrol. Research in Washington has shown that both bitterbrush (Purshia sp.) and ponderosa pine support populations of Deraeocoris, one of the more effective psylla predators. Douglas fir, native filbert, oak and willow are also reservoirs of the generalist predators feeding on psylla. Dr. David Horton of the USDA-ARS lab in the Yakima Valley is studying the potential benefit of willow trees, which support populations of anthocorid bugs, planted near pear orchards. He and others are investigating how orchard cover crops might be managed either by mowing or by the composition of plant species to better sustain natural enemy populations in the orchard.
|Pears are much less tolerant of spider mite populations than are apples. Leaf browning and drop occur with population levels that are far lower than those that damage apple foliage. Anjou is the most sensitive of the common cultivars grown in Washington, with Bartlett and Bosc being slightly more tolerant. In addition, pears can tolerate few rust mites, as pear rust mites feed on and russet the fruit. Apples can support very high numbers of apple rust mites with no damage to fruit or foliage, and these rust mites, together with more abundant spider mites, allow the predatory phytoseiid mites to maintain their populations and provide effective biological control. With low rust mite tolerance in pears the opportunities for biological control of spider mites are very limited, and most growers need to rely upon the use of miticides.
Some growers have found predatory mites in their pears and have gained a limited biocontrol benefit, particularly with more tolerant cultivars like Bosc or Asian pears. When pyrethroid insecticides were used post-bloom they effectively killed all predator mites and spider mite populations were much worse than those found in most pear blocks today, indicating that the predator mites are providing some help in spider mite control. Perhaps the main objective for most pear growers regarding mites and biological control should be to avoid using miticides, such as Carzol, that can disrupt psylla biocontrol.
|Mealybugs, primarily the grape mealybug (Pseudococcus maritimus), infest pear trees in most pear producing districts in the Western US but are generally not considered a major pest. They feed on the foliage and produce a honeydew that causes a coarse, black russet on the fruit. Within the past fifteen years they have become a much more serious pest in a growing number of orchards in north central Washington, attacking pears as well as, to a lesser extent, apples and apricots. The reasons for this increased pest status are unclear, possibly relating to a race of mealybug better adapting to these hosts, the development of resistance to common insecticides, or the elimination of natural enemies due to historically heavy pesticide use. On pears, mealybugs can cause nearly total crop loss in severely infested orchards. Pear growers with mealybug infestations have come to rely upon two, three or more applications of insecticides, mostly organophosphates, to get adequate control, effectively eliminating any chance for biocontrol of psylla as well as mealybug. With the potential loss of organophosphates looming with the implementation of the FQPA, some pear growers may be left grasping for effective alternative control programs.
There are natural enemies of mealybug that feed upon this pest, including generalist predators like lacewings, ladybird beetles, predaceous bugs and earwigs, as well as a cecidomyiid fly (Leucopsis) with predatory larvae. Several parasites have been identified as attacking mealybug, most commonly the wasp Acerophagus. Mealybug populations are frequently reduced to non-damaging levels in pear blocks where soft pesticide programs are used for several years. However, for the populations of natural enemies to build to adequate numbers can require that high mealybug populations be endured for several seasons, resulting in serious crop loss and potential financial disaster for the grower. There are few examples of mealybug infested blocks being cleaned up by biological control agents without significant damage to fruit. Developing biological control of mealybug will be very difficult for most growers in north central Washington without new insecticides or a better understanding of how to use the ones now available. Dr. John Dunley of the WSU-TFREC in Wenatchee is investigating grape mealybug biology and biological control.
The choice of insecticides has a large impact upon the success or failure of biological control of pear pests. Currently registered insecticides vary considerably in their effect upon natural enemies. Pear producers in British Columbia, and a number in Washington and Oregon, use Imidan for codling moth control because of its lesser impact upon many psylla predators. The following chart, prepared by Dr. Helmut Riedl of the Mid-Columbia Agricultural Research and Extension Center in Hood River, Oregon, summarizes insecticide effects upon several natural enemies.
|Pesticide||Anthocorids||Predatory Plant Bugs (Mirids)||Lady Beetles||Lacewings||Parasitic wasps||Predatory mites|
Ted Alway, Editor
Phone: (509) 664-5540
Fax: (509) 664-5561
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
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