Pacific Northwest Vegetable Extension Group

of Washington State University, Oregon State University, and University of Idaho

Alert Archives

Zebra Chip: July 23, 2013

Photo of plant with zebra chip This plant has zebra chip (confirmed by laboratory tests for Lso). The tuber (below) shows typical symptoms. Zebra chip has only been reported in a few fields this season. This is one of them.

Photo of tuber with typical zebra chip symptoms

The following report was sent earlier today from Phill Hamm, Jordan Eggers, and Silvia Rondon at the OSU HAREC… “Positive Zebra Chip infected plants have been found in the Columbia Basin. The zebra chip pathogen, ‘Candidatus Liberibacter solanacearum’ has been detected in potato plants from two fields southeast of Pasco, WA. The incidence of the disease is very low. To date, all psyllid samples submitted to the OSU HAREC Plant Pathology Laboratory have tested NEGATIVE for the zebra chip pathogen. Zebra chip is a manageable disease but, as with many diseases, 100% control is not possible or should even be the goal. Growers are recommended to maintain regular insecticide programs which will help limit the infection in and spread of the pathogen in potato fields. Please feel free to contact Phillip Hamm or Jordan Eggers if you have any questions regarding this disease.” If you find potato psyllids or plants with zebra chip symptoms (see photo on side bar), please let us know by sending an email to I will help you submit them for testing.

Carrie H. Wohleb, Ph.D.

Potato Insect Monitoring Report for the Columbia Basin of Washington: May to June 2014

Beet Leafhoppers (BLH): This is the most important time to watch for beet leafhoppers, because potatoes are more easily infected with BLTVA during the first 8 weeks of plant growth. As expected, we are not finding many BLH on our sticky traps now. BLH numbers usually begin to increase in mid-late May, and peak in June. It is the rapidly peaking flights of BLH that are important to detect. We recommend that you worry about BLH when average catch rates reach 40-100 per week.

Beet leafhoppers are important pests because they transmit BLTVA, a phytoplasma that causes purple top disease in potatoes. Research indicates that about 35% of the BLH in the Columbia Basin are infected with BLTVA. 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” (PDF). 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. A typical weekly catch during peak BLH activity is 100.

Eliminating weed hosts (wild mustards, Russian thistle, kochia) in areas surrounding potato fields is an important cultural management approach for BLH. 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 best. Remember to always read and follow instructions on the pesticide label, and don’t apply the insecticides below labeled rates. 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 (PDF).

POTATO PSYLLIDS: We will begin deploying traps for monitoring potato psyllids in late May. Last year we found our first potato psyllid the last week of May. The field we found it in was very close to wetland areas harboring bittersweet nightshade plants. Potato psyllids in the Pacific Northwest are known to overwinter on this perennial relative of the potato. Bittersweet nightshade is often found growing under Russian olive trees in wastewater ways and marshy areas. Potato fields near areas harboring bittersweet nightshade may be particularly at risk of early infestation with potato psyllids. 

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 lead to serious economic losses in some regions. ZC was first detected in potato fields in the Columbia Basin in 2011. 

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 (PDF). 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 prevent 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 nymphal population. Psyllid control programs should be in place prior to population establishment. One way to manage psyllids is to start with a neonicotinoid insecticide at planting, followed by foliar insecticide applications. Neonicotinoids applied at planting appear to provide 80-90 days of residual control of psyllids. It is recommended that no more than 80% of fields on a farm be treated with Group 4 neonicotinoids at planting. 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 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 (PDF).

APHIDS: We will begin sampling potato fields for aphids in late May.  Potato fields that were not treated with a neonicotinoid insecticide at planting are more likely to become infested with aphids this time of the season and should be monitored closely. Growers who treated potato fields with a systemic insecticide at planting, such as imidicloprid, thiamethoxam, or chlothianidin should expect about 80-100 days of control.

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 has caused substantial yield and tuber quality losses in the Columbia Basin. 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. 

Potato growers should monitor fields for aphids at least once a week, because early recognition and control of aphids is the next-best tactic in limiting spread of potato viruses, especially PLRV. Current recommendations are to treat long-season storage potatoes as soon as wingless aphids are detected. Low tolerances have been established because even a low incidence of seed borne PVY and PLRV can spread rapidly if aphids go unchecked.

POTATO TUBERWORM (PTW): We will begin deploying traps for monitoring PTW moths in mid-May.

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” (PDF). 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.
Read Full Report

Pest Data Mapping: View the weekly insect pest monitoring data in a map format. The map is color-coded so you can see at a glance where pest populations are lowest and highest across the region.

The 2014 Regional Sampling Network for Insect Pests of Potato in the Columbia Basin of WA is funded by a grant from the Washington State Potato Commission.

The project is managed by Carrie Wohleb, WSU with support from Tim Waters, WSU and Andy Jensen, WSPC IPC OPC

Please report pest outbreaks so they can be shared in a general way with other potato growers across the Basin. Send reports, questions, or comments to

Late Blight: June 18, 2014

Dr. Dennis Johnson's late blight information hotline was updated on June 18. Weather has been favorable for late blight with rain and cloudy conditions occurring in various locations in the Columbia Basin on June 13, 16 and 17.  Late blight has not been reported as of this date.  Probability that late blight will occur in the Columbia Basin is 85%.  Fields should be treated with a late blight fungicide before any major rainfall.  Fungicides applied 1 to 3 days before major rainfall will be most effective and those applied longer than 7 days will not be effective in checking late blight.  Check 10-day weather forecasts daily and monitor fields thoroughly and frequently for late blight. Pay attention for late blight near the pivot center, wheel lines, in low lying areas, by fields that had late blight last year, and in fields by cull piles.  Please contact Dennis Johnson at 509-335-3753 to report, confirm, or to make a late blight diagnosis.  The hotline number is 1-800-984-7400.

Don’t hesitate to send questions or comments to

The following is a checklist for managing potatoes in storage that may contain late blight infected tubers. This information was presented in an article by Dr. Dennis Johnson in a recent issue of Potato Progress...
  1. Continue late blight fungicide applications until harvest or until all vines are dead.
  2. Harvest only during dry weather.
  3. Harvest when tuber pulp temperature is 45–65 degrees F.
  4. Store known infected tuber lots separate from non-infected lots, and where they can be easily obtained for processing.
  5. Sort for rot going into storage – provide sufficient light and people to do the job.
  6. Provide adequate air flow throughout the storage (25 cfm/ton).
  7. Cool and dry tubers as quickly as possible.
  8. Cure tubers at the lowest temperature possible (50 degrees F) or eliminate the curing period, depending on the amount of rot. Then cool the pile to the final storage temperature as quickly as possible. It may be necessary to hold tubers for processing and chips below the typically recommended temperatures.
  9. Do not humidify.
  10. Run fans continuously. Recirculate air through the tubers at all times, even when outside air is not being introduced.
  11. Keep piles shallow to promote air movement and removal of hot spots.
  12. Monitor storages daily. Determine temperature of the pile at various depths and locations. Serious late blight problems usually show up within 6 weeks of storage.
  13. Do not expose cold tubers to outside air and any tubers to air at or below freezing.
  14. Tubers of Alturas and Umatilla are moderately resistant, and tubers of Defender are resistant. Storage problems with these cultivars should be less than with other cultivars. However, good air movement and temperature and humidity management will be needed when storing infected tubers of all cultivars.


First reports of tomato late blight in Louisiana, Florida and Maryland. Information on major outbreaks of late blight on tomato in the southeast and northeast USA. Michigan State University

Late Blight Hits Tomato Plants In Gardens, Nursery.

Late Blight Photos & Management Recommendations

Tomato and Potato Late Blight Alert Press Release (DOC). University of Idaho. The accompanying leaflet (PDF) from Michigan State University includes photos and tips to prevent late blight.

Tomato Late Blight

Potato Late Blight

Potato Late Blight. Plant Management Network International. (video)

Home gardeners: Kill diseased tomatoes and potatoes to prevent late blight next year, Michigan State University Extension, 2009.

Good garden sanitation practices now can prevent plant diseases next season, Michigan State University Extension, 2010.

A potato late blight forecasting model for the Columbia Basin can be accessed via the WSU AgWeatherNet website at Subscription to AgWeatherNet is free of charge.

Zebra Chip: September 2, 2011

Zebra Chip, a disease seriously impacting potatoes produced in Texas and other Southwest states in recent years, has been found impacting potatoes in the southern Columbia Basin in 2011. See the message from Phil Hamm, Oregon State University, to the Washington Potato Growers and allied industries: Phil Hamm’s message to industry. Included here are informational items about this disease and its vector. Please contact Andy Jensen, 509-765-8845 or Phil Hamm with questions.

Photo of potato affected by Zebra Chip

A photo of tuber symptoms post peeling.

Information on the psyllid (PDF).

Information on the disease and recent research:
History in the Making: Potato Zebra Chip Disease Associated with a New Psyllid-borne Bacterium – A Tale of Striped Potatoes, Texas Agrilife Research and Extensioin Center at Amarillo.

Exemption Granted For Use of Movento® to Control Thrips on Dry Bulb Onions in Washington State: March 24, 2011

Washington Onion Producers received a Section 18 granting document (PDF) and product label (PDF) for Movento® use for thrips control in onions in Washington State. Contact Tim Waters, WSU Area Extension Educator Franklin & Benton Co. if you have any questions, or 509-545-3511.

Brown Marmorated Stink Bug: October 8, 2010

In 2004, Oregon State Dept of Ag documented a new stink bug called the brown marmorated stink bug in the Portland area. It is new to North America and is currently causing significant damage to multiple key crops (including stone fruit and some vegetables like beans) in the Eastern US. The pest has not been recorded in Washington State yet. The adults are active in the fall and often aggregate on the sides of houses in preparation for wintering. It is important to get samples identified properly and recorded as there are a few native stink bugs that look like brown marmorated stink bug. The quick ID guide, Pest Alert: Brown Marmorated Stink Bug (PDF), from Oregon Department of Agriculture provides additional information.

Aminopyralid Toxicity to Vegetables from Pre-plant Compost Application: August 31, 2010

Aminopyralid Residues in Compost and other Organic Amendments. Washington State University Whatcom County Extension.

Herbicides in Compost, Washington State Department of Agriculture Pesticide Management Division (PDF, 2010)

The Allowance of Green Waste in Organic Production Systems. Organic Materials Review Institute. 

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