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Green Peach Aphid Management in Potatoes

Keith S. Pike
Washington State University-Prosser
24106 N Bunn Rd
Prosser, WA 99350-8694
509-786-9269
509-786-9370 (fax)

Project Duration: 1 year (07/2000-06/2001)

 Matching Funds
  Request Non-Federal Federal
First Year Funding 25,422 42,092
Total Funding Request 25,422 42,092  

Abstract

Green peach aphid has been a significant pest of potatoes in the Pacific Northwest for many years because of its capacity to transmit potato leafroll virus (PLRV). Despite advances in integrated pest management, and frequent use of insecticides, the industry is still plagued by the insect. Adding to the problem is the fact that the aphid is also occurring in seed production areas, which is increasing the risk of PLRV in seed stocks. Systemic insecticides protect against early season aphids, while foliar-applied materials give mid- to late-season control. For the latter, the product of choice has been Monitor insecticide. But in the last year, bioassay testing has shown that at least some populations of the aphid are now resistant to the chemical, meaning there is a need to shift emphasis from reliance on Monitor, to broader use of biological agents and softer chemicals. The objectives of the project are to enlarge and protect the pool of biological agents attacking green peach aphid; promote the use of soft chemicals; determine the level of aphid population resistance to Monitor® insecticide in seed and commercial production areas; and communicate research findings and management recommendations to growers via website and hotline media.

Objectives

  1. Enlarge and protect the pool of biological agents attacking green peach aphid; promote the use of soft chemicals.
  2. Determine the level of aphid population resistance to Monitor® insecticide in seed and commercial production areas.
  3. Communicate recommendations to growers via hotline and website media.

Justification

Green peach aphid, as a vector of potato leafroll virus (PLRV) is a major pest player in the production of potatoes. Despite advances in pest management, the industry is not free of this insect. Adding to the problem is the fact that the aphid can sometimes be found in seed production areas. Green peach aphid populations can be highly variable between seasons and across areas. Systemic insecticides provide early season protection (ca. 7-12 weeks), while foliar-applied materials, if timed properly, control the aphid during the summer growing period unless resistant populations occur.

Literature Review

Green peach aphid population levels have increased and seasonal occurrences have changed significantly in Pacific Northwest potato fields since 1996 (Schreiber et al. 2000). In 1999, massive populations of winged and wingless aphids were observed, along with widespread occurrence of potato leafroll virus in the Washington-Oregon Columbia Basin potato region. A number of factors have contributed to these changes: 1) unseasonably warm temperatures during the winter months leading to high survival of green peach aphids on winter annuals and perennials, 2) high incidence of volunteer potatoes constituting an early source of aphid-virus problems, 3) increased virus incidence in seed potatoes, 4) reduced or no controls implemented on short season processing potatoes (cost cutting measure, but contributes to increased aphids impacting the longer growing storage potatoes), 5) increased acreage of short season processing potatoes, 6) use of pyrethroids (controls Colorado potato beetle) that disrupts or destroys natural enemies, and causes flare ups in aphid numbers, and 7) increased aphid resistance to Monitor insecticide (Boydston & Seymour 2000, Newberry & Thornton 2000, Pike 2000, Schreiber et al. 2000).

It was previously thought that for the Northwest, the primary means by which green peach aphid survived the winter was in the egg stage on peach. It is now known that in a mild winter, the aphid also survives on various perennials and winter annuals, such as tumble mustard, flixweed, shepherdspurse, mallow, horseweed, pennycress and redstem filaree (Pike 2000). While it is not entirely possible or practical to control aphids originating from these weeds, it is important to understand that early sources of aphid outbreaks can occur throughout most, if not all of the Pacific Northwest potato growing regions as these weeds dry out (Mowry et al. 2000).

Monitor insecticide has been the chief product of choice as a foliar applied treatment for years. It's usefulness may be drawing to a close; recent findings show that selected populations of green peach aphid have become resistant to the insecticide (Pike & Whalon unpubl. data). Monitor will be used in 2000 on many farms, but the direction for the future lies in improved IPM approaches, which will involve protecting existing and newly introduced biological control agents in concert with target directed systemics and softer foliar treatments (Fulfill®, Success®). As part of a work in progress, a draft IPM program has been posted at a website as a guide for grower and field consultant for the 2000-crop year (http://www.wsu.edu/~potatoes).

The status of biological control of green peach aphid in the western United States was reviewed by Biever (1995). Interestingly, previously published work on natural enemies centered on the peach ecosystem rather than potatoes (Tamaki et al. 1967, Tamaki and Halfhill 1968, Tamaki and Weeks 1968, Tamaki 1972, 1973, and Tamaki et al. 1981). From Biever's review, several recommendations were made concerning biological control. Two of these were to: 1) develop a methodology to use exotic and native natural enemies as classical and augmentative biological control agents, and 2) introduce and evaluate exotic species of parasitoids and fungi.

Already in Washington, aphid attacking parasitic wasps have been successfully used in small grains to reduce Russian wheat aphid populations to non-pest levels (Pike et al. 1997, 1999). Some of these new introductions, in addition to attacking the target aphid, are also utilizing green peach aphid (Pike et al. 1999, 2000). Up to now, parasitoids have been subject to substantial toxic sprays in potatoes, which has limited their occurrence and activity in the crop. The use of more selective insecticides (Success for Colorado potato beetle; Fufill for green peach aphid) will afford greater opportunity for the parasitoids to be successful. A new parasitoid strain of promise in controlling green peach aphid, both in and outside of potatoes, is Aphidius colemani (Chilean strain). Mass production of this strain commenced last year and will continue into 2000. Some recoveries of the parasitoid have already been made, indicating it is adapting to its new environment (Pike et al. 2000).

Approach and Methods

  1. Biological Control (continuation of work begun in 1999), and use of soft chemicals—New aphid-specific wasp parasitoids (aphidines) of green peach aphid, mass reared in insectary facilities at WSU-Prosser & Pullman, will be released for permanent establishment throughout the Columbia Basin, both inside and outside potato fields. Approximately 100,000 parasitoids will be introduced in areas of Adams, Benton, Franklin, Grant, Kittitas, Klickitat, Walla Walla, and Yakima counties in 2000. In addition, the impact of target directed (systemic) and foliar applied-insecticides (both standard and new soft chemicals) on parasitoids will be evaluated under field conditions at Hermiston [collaborative research with G. Reed].
  2. Aphid Monitor Resistance - First year bioassays of populations from different sites in Washington's Columbia Basin confirmed the presence of developing resistance in green peach aphid to Monitor insecticide, which means Monitor may have limited utility in the future. Second year studies are needed to clarify the product's performance in Washington, and from sites outside the state where potato seed is obtained. Poor control of aphids in seed producing areas has resulted in higher levels of PLRV-infected seed, and subsequently higher levels of virus in commercial potatoes. Monitor has been the product of choice as a foliar treatment, but if resistance proves widespread, it will need to be replaced by other management approaches. Recognition and confirmation of resistance is intended to help the industry move to more effective controls, and to leverage for new product registrations of merit, with the emphasis on soft chemicals. Out-of-state collections from different seed producing areas will be provided by collaborating scientists (T. Mowry - Idaho; S. Blodgett - Montana ; G. Reed - Oregon); bioassays will be in cooperation with M. Whalon at Michigan, and probably with an incoming scientist to be located at the WSU-Food and Environmental Quality Lab, Richland, WA.
  3. Recommendations - An aphid hotline (1-888-673-6273) and website (http://www.wsu. edu/~potatoes) have been instituted to communicate information. These outlets for information will be updated regularly to keep the industry current with the critical happenings and best management approaches. Updates will be based on research findings, and on field survey, sampling, and evaluation of pest populations taken weekly across central Washington. Field evaluations will include both short and long season potatoes. Fields to be sampled will be chosen with the cooperation of growers at the start of the season. Running records will be kept on the field history, crop growth and condition, earliest aphid flight, and pattern of pest population development. The hotline and website will be coordinated with Oregon State University scientist G. Reed, and other cooperators as applicable.

Impact Assessment

The potato industry will be timely informed on aphid status and current treatment recommendations. The merits of Monitor insecticide for controlling green peach aphid will be clarified, and pesticide risk to parasites defined. New aphid-selective parasites will be established to enhance green peach aphid biocontrols (new parasites to be self-sustaining in the environment).

Appendix A. Literature Cited

Biever, K. D. 1995. Green peach aphid, pp. 127-128. In J. R. Nechols (Exec. Ed.), Biological Control in the Western United States, Accomplishments and Benefits of Regions Research Project W-84, 1964-1989. Univ. of California, Div. Agric. & Nat. Resources Publ. 3361, 356 pp.

Boydston, R. & M. Seymour. Volunteer potato outlook for 2000. Wash. Potato Commission Spud Topics 45(15).

Mowry, T., K. Pike, D. Ragsdale, G. Reed, A. Schreiber, & B. Stoltz. Integrated pest management program for green peach aphid & potato leafroll virus for Pacific Northwest potatoes. http://www.wsu.edu/~potatoes

Newberry, G. D. & R. E. Thornton. 2000. After harvest tuber leavings - potential for volunteer problems. Wash. Potato Comm. Spud Topics 45(15).

Pike, K. S. 2000. Aphid Hotline: http://www.wsu.edu/~potatoes.

Pike, K. S., P. Stary, T. Miller, D. Allison, L. Boydston, & G. Graf. 1999. Host range and habitats of the aphid-parasitoid Diaeretiella rapae (M'Intosh) (Hym.: Aphidiidae) in Washington State. Environ. Entomol. 28: 61-71.

Pike, K. S., P. Stary, T. Miller, D. Allison, L. Boydston, G. Graf , & R. Gillespie. 1997. Small grain aphid parasitoids (Hymenoptera: Aphelinidae and Aphidiidae) of Washington: distribution, relative abundance, and seasonal occurrence; and key to known North American species. Environ. Entomol. 26: 1299-1311.

Pike, K. S., P. Stary, T. Miller, G. Graf, D. Allison, L. Boydston, and R. Miller. 2000. Aphid parasitoids (Hymenoptera, Braconidae, Aphidiinae) of Northwest USA. Proc. Entomol. Soc. Wash. 102: (in press).

Schreiber, A., G. Reed, and K. Pike. 2000. Green peach aphid is changing, so should you. Wash. Potato Comm. Spud Topics 45(13).

Tamaki, G. 1972. The biology of Geocoris bullatus inhabiting orchard floors and its impact on Myzus persicae on peaches. Environ. entomol. 1: 559-565.

Tamaki, G. 1973. Spring populations of the green peach aphid on peach trees and the role of natural enemies in their control. Environ. Entomol. 2: 186-191.

Tamaki, G & J. E. Halfhill. 1968. Bands on peach trees as shelters for predators of the green peach aphid. J. Econ. Entomol. 61: 707-711.

Tamaki, G. & R. E. Weeks. 1968. Use of chemical defoliants on peach trees in an integrated program to suppress populations of green peach aphids. J. Econ. Entomol. 61: 431-435.

Tamaki, G., B. Annis, & M. Weiss. 1981. Response of natural enemies to the green peach aphid in different plant cultures. Environ. Entomol. 10: 375-378.

Tamaki, G., B. J. Landis, & R. E. Weeks. 1967. Autumn populations of green peach aphid on peach trees and the role of syrphid flies in their control. J. Econ. Entomol. 60: 433-436.

Appendix B. Timetable

Project is 1 year in duration

Appendix C. Major Participants

Project Leader:

K.S. Pike, Entomologist, WSU-Prosser,
24106 N. Bunn Rd, Prosser WA 99350-8694, ph. 509/786-9269, FAX 786-9370, kpike@tricity.wsu.edu

Collaborators:

Project Budget

Project Period: 07/2000 to 06/2001

Budget Category

Grant Funding

 Other Funding1 Total Funding
Personnel
5,7002
 30,035 35,735
Fringe Benefits (26%) 1,482 7,809 9,291
Goods and services3 3,450 3,450
Travel 4,250 4,250
Equipment      
Supplies      
Contractual4 8,000   8,000
Other: (Indirect Costs) 6,790   6,790
Total 25,422 42,094 67,516

1Washington Potato Commission funding.
2 Person handles parasitoid rearing & management (partial funds, D. Graf)
3 Insectary supplies, postage for live shipments, hotline & website maintenance
4 Monitor insecticide bioassays

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