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Washington State University Extension
WSU POTATO ALERTS
Hello Potato Alert Subscriber: This is the 3rd potato alert issued for the 2021 growing season.  If this message was forwarded to you and you would like to subscribe, click HERE and choose "Potato Pest Alert" and any other topics that are important to you.  
TABLE OF CONTENTS
Click on the links below to advance to the topics that interest you.
INSECT MONITORING REPORTS:
IPM GUIDES & SUPPORT:
IPM GUIDES & INFO
DIAGNOSTIC LABS

PREVIOUS REPORTS:
WSU POTATO ALERT - March 25, 2021
WSU POTATO ALERT - March 16, 2021
WSU POTATO ALERT - Sept. 11, 2020
INSECT MONITORING REPORTS
week of May 14, 2021
INSECT MONITORING NETWORK:  This is the 12th year of the WSU Extension Potato Insect Pest Monitoring Network.  We have deployed insect traps in 47 commercial potato fields across the Columbia Basin, from Quincy to Paterson. Our scouts will be visiting these fields each week to collect sticky cards and examine plants for several important insect pests.  We will be looking for: aphids, beet leafhoppers, Colorado potato beetles, lygus bugs, potato psyllids, potato tuberworm, and spider mites.  I'll let you know what we are finding each week in these WSU Potato Alerts, which will be sent every Friday.     

Please report unusual pest and disease activity.  Many pests and disease problems should be managed on a region-wide basis to minimize the impact of outbreaks.  Send an email to Carrie Wohleb at cwohleb@wsu.edu to report.  Your comments and observations are always welcome.
COLORADO POTATO BEETLE:  Colorado potato beetles (CPB) have been seen in many potato fields in the Lower Columbia Basin.  The adults have been laying eggs and larvae are beginning to hatch.  Adults are not usually heavy feeders, but the larvae have huge appetites.  CPB populations can get very large and cause significant defoliation and yield losses if their numbers go unchecked. 
The pictures above show Colorado potato beetle 1) eggs (left), 2) larvae (middle), and 3) adult beetles (right).  This is one of the easiest potato pests to scout.  You are most likely to find them now on the borders of your potato fields.  
MANAGING COLORADO POTATO BEETLES WITH INSECTICIDES:  If you applied a neonicotinoid insecticide at planting (or shortly thereafter), then you should get at least 50-60 days of CPB control.  In some cases you could get as many as 90 days of control.  If not, then a well-timed insecticide application can control CPB.  The key is targeting your application to the right life stage.  Most insecticides with activity against CPB work best when the larvae are newly hatched and small.  It is recommended that you time the application when 50% of the larvae have hatched from eggs.   

Some products labeled for CPB control include:  various neonicotinoids (Admire, Cruiser, Actara, Assail, Belay, etc.), abamectin (Agri-Mek, etc.), cyazpyr (Exirel), flupyradifurone (Sivanto), methomyl (Lannate), novaluron (Rimon), oxamyl (Vydate), phosmet (Imidan), spinetoram (Radiant), spinosad (Blackhawk), rynaxypyr (Coragen), and tolfenpyrad (Torac).  Pyrethroids (IRAC Group 3) (Mustang, Warrior, Capture, etc.) can also be used to control CPB, but they are not recommended after June 15, because they also kill beneficial insect predators that help to keep pests like aphids, thrips, and spider mites in check.  It is very common to see flare-ups of these pests when pyrethroids are used after mid-June.  Be aware that many insecticide products combine pyrethroids with another mode of action (e.g. Leverage, Brigadier, Hero, Voliam Xpress, Endigo) and these also should not be applied after June 15.

Don't apply a foliar neonicotinoid (any IRAC Group 4A insecticides; e.g. Leverage, Assail, Endigo), if a neonicotinoid was applied to the seed or soil at planting or hilling.  The risk of CPB and some other pests (like potato psyllids) developing resistance to neonicotinoid insecticides is high and we encourage you to limit their exposure to these insecticides.

Read the product label carefully for specific use instructions.  Some products should not be used with sticker/binder type adjuvants (e.g. abamectin, thiamethoxam).  Some insecticides degrade if the spray solution is acidic (e.g. spinosad, spinetoram), others degrade if the spray solution is alkaline-neutral (e.g. phosmet).  These products are not going to work very well if you don't pay attention to these details.
BEET LEAFHOPPERS:  We are finding beet leafhoppers (BLH) on several traps around the Basin.  They were collected on 72% of our sticky traps this week.  Most traps had low numbers of BLH.  However, there appears to be a few "hot spots" around the Basin that are collecting higher numbers.  

The maps below show interpolated BLH population densities across the region using out trapping network results.  The pest densitiy maps were developed and validated by the Crowder Laboratory, WSU Entomology.

MORE ABOUT BEET LEAFHOPPERS:  Beet leafhoppers (BLH) are considered important pests of potato because they can transmit a phytoplasma (BLTVA) that causes purple top disease.  Since BLH are transient, or pass-through pests of potatoes, they may be gone by the time you see any purple top symptoms.  That is why we monitor BLH using a network of yellow sticky cards.  It allows us to track BLH populations as they develop and move through the region.     
Beet leafhoppers actually prefer to feed on weeds like tumble mustard, Russian thistle, and kocia.  They also like beets (no surprise) and radish.  But, when preferred weeds or crops are not immediately available, they look for something else to eat and that's when they come across your potato crop.  Unfortunately, it does not take long for them to infect potato plants with BLTVA as they search for food.  

Many potato fields in the Columbia Basin are near or even surrounded by patches of tumble mustard.  The tumble mustard is probably home to many BLH in the spring.  As long as the mustard is green and growing, the BLH are probably happy to stay put.  But, the weeds will eventually dry down and the BLH will be forced to move.    
WEED CONTROL TO MANAGE BEET LEAFHOPPERS?  Eliminating large tracts of weeds may help to keep BLH numbers in check.  However, it is best to remove weeds before nearby crops emerge.  Otherwise, you may flush the BLH out of the weeds and into your crop.  Controlling BLH on weeds in rangeland areas (using approved insecticides) may be an effective tactic for managing purple top on large farms, where continuous tracts of land can be managed.  But, it won't work for smaller or fragmented farms without regional coordination.
INSECT MONITORING NETWORK RESULTS TABLE:  This table is provided for the benefit of the growers who participate in our insect monitoring network.  The insect trap counts and sampling results from each field are shown below.  This table is color-coded to highlight where insects were found and how their numbers ranked based on historical trapping/sampling results.  
 
DISEASE REPORTS
week of Sept. 11, 2020
LATE BLIGHT:  Update provided by Dr. David Wheeler, WSU Plant Pathology, for May 14, 2021.  

FORECAST:  Late blight has not been reported in the Columbia Basin of Washington.  Additionally, late blight is not expected to occur in the Columbia Basin before row closure.  The probabilities that late blight will occur in 2021 are presented below for the same locations used in previous years:
  • Othello: 0.77
  • Tri-Cities: 0.74
  • Prosser: 0.51 
RECOMMENDATIONS:  
  1. Eliminate culls, tuber refuse, and volunteer potato plants, especially in fields with or near late blight last year.
  2. Limit irrigation unless the crop is fully emerged.
  3. Ensure that developing tubers are covered with moderately sized hills.  
  4. Upon row closure, begin to monitor fields for late blight.  This is very important for (i) effective management and (ii) accurate forecasting.  Growers, field representatives, and extension specialists serve as the eyes on the ground.  We need this information to provide meaningful forecasts.
CONTACT:  David Wheeler (david.wheeler@wsu.edu; (215) 880-3024) to confirm or to diagnose late blight.
The pictures below show symptoms of late blight on potato leaflets and petiole (photos by Tim Waters, WSU).    
NEMATODE REPORTS
week of May 14, 2021
DISCLAIMER:  The following information is not intended to be an exclusive endorsement for the use of oxamyl (Vydate CL-V and ReTurn XL) in suppressing populations of nematodes in potatoes.  There are several other products labeled for the suppression of nematodes in potatoes in Washington, including but not limited to: metam sodium (e.g. Vapam), dichloropropene (e.g. Telone), ethoprop (Mocap), fluopyram (Velum Prime), and spirotetramet (Movento). 

DEGREE DAYS FOR OXAMYL APPLICATION:  Applications of oxamyl for the suppression of nematodes should be synchronized with nematode life cycles.  Properly timed oxamyl applications are based on soil degree day (DD) accumulations for your area; DD models for root knot nematodes are based on soil temperature at a 6-9 inch depth and a developmental threshold of 41 degrees F.  The table below was provided by Corteva representatives to help growers plan their oxamyl applications.  It is recommended that the second chemigated application (first is at emergence) should be applied at 1440 DDs (local Corteva reps. suggest going ahead with application at 1375 DDs).  Please refer to the label for details. 

It will still be a few weeks before we reach 1440 DDs anywhere in the Columbia Basin.  Note that DDs are being monitored at five locations this year (it was just three last year).
ADDITIONAL PEST & DISEASE MANAGEMENT INFORMATION
IPM GUIDES & INFORMATION:  Click on the links in blue

NW Potato Research  This website has lots of images of insect pests and beneficial organisms, monitoring information, and pest management guides.

The IPM Guidelines for Insects and Mites in Idaho, Oregon and Washington Potatoes  This guide has detailed pest management information.  It includes many recommendations on selecting insecticide products.

The 2021 PNW Insect Management Handbook
The 2021 PNW Plant Disease Handbook
The 2021 PNW Weed Handbook

WSU Pesticide Information Center OnLine (PICOL) Database  PICOL contains selected information from pesticide products registered in OR and/or WA.  The site provides PDFs of most labels.

IPM Strategic Plan for Potatoes in Oregon, Washington and Idaho  This report was written to identify pest management priorities and to help establish future strategies to increase and improve IPM in potatoes.

The University of Idaho - Psyllid Management

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.

OMRI Products Lists  This website has a list of products and materials allowed for organic use.

Pacific Northwest Vegetable Extension Group: Photo Gallery of Potato Problems  If you are looking for images of potato pest and disease problems, visit this website. 
PLANT PEST DIAGNOSTIC CLINICS: The clinics may have limited hours of operation due to restrictions necessitated by COVID19.  Visit the websites below and contact the lab managers to ensure your samples are received and processed as needed.  Some of these labs also offer digital diagnostic services (using photos, descriptions, and management information). 

HAREC Plant Pathology Lab in Hermiston, OR

U of ID Plant Diagnostic Labs in Parma, ID and Idaho Falls, ID
PESTICIDE 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. 
ACKNOWLEDGMENTS:  The WSU Potato Alerts and the insect monitoring network are funded by potato growers through a grant of the Washington State Potato Commission and is managed with the cooperation of potato growers and crop consultants across the Columbia Basin.  THANK YOU!
Have a great growing season! 

Questions or comments can be directed to:

Carrie H. Wohleb, Ph.D.
Regional Vegetable Extension Specialist
Washington State University
1525 E. Wheeler Rd.
Moses Lake, WA 98837
Tel: (509) 707-3510
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