INSECT PEST INFORMATION
BEET LEAFHOPPERS (BLH)
Beet leafhoppers are important pests because they transmit BLTVA, a phytoplasma that causes purple top disease in potatoes. They are considered a transient or pass-through pest of potato. Unfortunately, they stay long enough to infect potatoes with BLTVA. Their preference for other plants usually keeps the damage in potato fields to a minimum and near the edges of the field, but more extensive damage can occur when BLH populations are large. In the Columbia Basin, the first spring generation of BLH usually migrates towards potato fields in late May and early June, with a peak flight in late June. Yellow sticky traps placed near potato fields are one way to monitor BLH. Information about setting up traps and identifying BLH can be found in the article, “Beet Leafhopper Monitoring with Yellow Sticky Cards”. Treatment thresholds based on BLH numbers on traps have not been established, but we know that the risk of infection increases as BLH populations become large. If the numbers on traps build up to 40 or more BLH per week, then it is probably time to be concerned.
Eliminating weed hosts (wild mustards, Russian thistle, kochia) in areas surrounding potato fields is an important cultural management approach for BLH. It is important, however, to time weed control carefully. Controlling vast sects of weeds when you have a newly emerged potato crop nearby may flush the BLH into your crop at a time when the potatoes are small and more susceptible to BLTVA infection and purple top. Potato growers may also select cultivars that are less susceptible to purple top (Ranger, Umatilla, and Norkotah are considered highly susceptible; Russet Burbank is susceptible; and Alturas and Shepody are moderately susceptible). A number of insecticides are labeled for use on potatoes to control leafhoppers. Systemic at-planting insecticides, especially those with longer residual activity applied at the maximum allowed rate, have been shown to provide some early season control of BLH. Results may vary depending on the product used, application rate, soil and environmental conditions, and insect pressure. Foliar insecticides may also be used to control BLH. These are usually applied in May, June, and sometimes July. Insecticides with long residual activity (10-14 days) are recommended, since two applications can provide almost a month of control. Insecticides with short residual activity are probably not cost-effective, since they would require multiple applications to maintain control. For more information about managing BLH, visit IPM Guidelines for Insects and Mites in ID, OR, and WA Potatoes and the PNW Insect Management Handbook.
Potato psyllids are important pests mostly because they can transmit a bacterium (Candidatus Liberibacter solanacearum) to potatoes that causes zebra chip disease (ZC). This disease reduces both yield and tuber quality and has led to serious economic losses in some regions. ZC was first detected in potato fields in the Columbia Basin in 2011. Potato psyllids can also cause psyllid yellows, a condition that results from psyllid nymph feeding on potato leaves. Psyllid yellows can reduce yields and tuber quality.
Potato psyllids usually start to move into potato fields in May or June in the Columbia Basin. Yellow sticky cards are recommended for detecting psyllid migration into an area. The cards should be placed inside the field, very near the field edge, and right above the canopy. We recommend using the AlphaScents brand sticky cards, because they are stickier than most sticky cards and hold up under irrigation. It is best to have at least four yellow sticky cards around the field, and more is better. For more information about trapping psyllids, read “Psyllid Monitoring with Yellow Sticky Cards”. Other life stages of the psyllid can be found by collecting several leaves (mid-plant) from the outside rows of the field, and then scanning the underside (with a hand-lens) for the tiny nymphs and eggs.
It is not possible to stop psyllids from migrating into potato fields, but it is possible to deter potato psyllid populations from establishing once they have landed. Population establishment is defined as potato psyllids successfully laying eggs that lead to development of a nymph population. Psyllid control programs should be in place prior to population establishment. One way to manage psyllids is to start with a systemic insecticide at planting or at layby, followed by foliar insecticide applications. The residual effect of the neonicotinoid will depend on the time and rate of the application and the rate of plant growth. If only foliar insecticides are used, then it is recommended that applications begin upon first detection of potato psyllids in your area. Potato psyllid trapping information for the Columbia Basin of WA is available via emailed pest alerts each week (contact firstname.lastname@example.org to sign up for emails). For more information about psyllids, including insect identification, monitoring, and control recommendations, read IPM Guidelines for Insects and Mites in ID, OR and WA Potatoes.
Aphids are important pests because they transmit several important potato viruses, especially potato leafroll virus (PLRV) and potato virus Y (PVY). Green peach aphids are the most important vector of PLRV, which can result in significant yield and tuber quality losses. PLRV causes net necrosis in some cultivars, an unacceptable tuber defect in processing potatoes. PVY can also result in significant yield losses, and some strains of the virus cause tuber defects. The tuber necrotic strains of PVY are becoming more prevalent in the PNW. The first step in preventing the spread of potato viruses is to plant certified seed potatoes with very low incidence of PVY and PLRV. Early recognition and control of aphids is the next-best tactic in limiting spread of potato viruses, especially PLRV.
In addition to spreading viruses, green peach aphids can cause significant feeding-damage that ends in the early senescence of plant foliage. Potato growers should monitor fields for aphids at least once a week, because it is important to catch infestations early before they become large. Large infestations can be difficult to control. It may require multiple insecticide applications to control a large population.
POTATO TUBERWORM (PTW)
Potato tuberworm (PTW) was first recognized as an important pest of potatoes in the southern Columbia Basin in 2003. PTW larvae feed on tubers causing damage that renders them unmarketable. Potato growers with fields south of Connell, WA are recommended to pay close attention to regional trapping data, and should deploy pheromone traps. Infestations of PTW are highly localized, and it is risky to conclude too much from traps that may be several miles away. Information about setting up traps and identifying PTW moths can be found in the article, “Tuberworm Monitoring with Pheromone Traps”. Trap counts from mid-season to harvest are particularly important to watch. Pre-harvest control measures may be warranted in fields where PTW moths in pheromone traps are found to be increasing every week, especially in August-October.
It can be very important to manage PTW in the weeks leading up to harvest. Most of the feeding-injury to tubers occurs after vine kill or senescence when the larvae move from the foliage to the tubers. Damage to tubers is usually more significant the longer the potatoes stay in the field under dead vines. Insecticide treatments beginning 4-8 weeks before harvest have been shown to reduce damage to tubers. It is very important to consider the pre-harvest interval when selecting a product to apply. Cultural practices that reduce tuberworm damage can be very effective. They include 1) eliminate cull piles and volunteers; 2) minimize the time between vine kill or senescence and harvest or harvest under green vines; 3) maintain soil moisture after vine kill to prevent soil cracking; and 4) maintain more than 2-inches of soil over tubers.
PESTICIDE USE DISCLAIMER
Application of a pesticide to a crop or site that is not on the label is a violation of pesticide law and may subject the applicator to civil penalties. In addition, such an application may also result in illegal residues that could subject the crop to seizure or embargo action. It is your responsibility to check the label before using any product to ensure lawful use, and obtain all necessary permits in advance.
- IPM Guidelines for Insects and Mites in ID, OR, and WA Potatoes Authored by PNW entomologists, this report is a set of recommendations as to how to best manage potato insect pests.
- PNW Insect Management Handbook This handbook is a tool for making decisions regarding the management of important insect pests in the PNW. For information about potato pests, select the Chapter: Irish Potatoes.
- Northwest Potato Research Consortium Find information about insect pests, insect-transmitted diseases, and beneficial insects.
- Beet Leafhopper Monitoring with Yellow Sticky Cards This article explains how to deploy yellow sticky card traps for monitoring beet leafhoppers. It also provides information about correctly identifying beet leafhoppers, as there are many look-alike leafhoppers in the Columbia Basin.
- Biology and Management of the Potato Tuberworm in the PNW This PNW Extension publication is an excellent resource for potato tuberworm information.
- Potato Psyllid Vector of Zebra Chip Disease in the PNW This OSU Extension publication provides extensive information about the biology, ecology and management of potato psyllid in the PNW.
- Recognizing Potato Psyllid Adults
- Psyllid Monitoring with Yellow Sticky Cards This article explains how to set up sticky traps for monitoring potato psyllids. It also explains how to identify them correctly, as there are several psyllid species they can be confused with.
- Tuberworm Monitoring with Pheromone Traps This article explains how to set up traps for monitoring tuberworm moths, and how to identify them correctly.
- University of California IPM Pest Management Guidelines – Potatoes
- Cornell University – Organic Production and IPM Guide for Potatoes This guide includes a chapter on insect management. The guide is aimed at Northeastern potato growers, so some of the information does not pertain to the Pacific Northwest. Keep in mind that we have a longer, hotter, and drier growing season and a different spectrum of pests.
- Pacific Northwest Vegetable Extension Group: Photo Gallery of Potato Problems If you are looking for images of potato pest problems.
PLANT PEST DIAGNOSTIC CLINICS
WSU Plant Diagnostic Clinic in Pullman, WA
OSU HAREC Plant Pathology Lab in Hermiston, OR
MONITORING REPORT ARCHIVES
This project is sponsored by the Washington State Potato Commission.