Hello Potato Alert Subscriber: This is the March 22, 2023 issue of WSU Potato Alerts, and the 1st issue for 2023.  These alerts relate to commercial potato production in the Columbia Basin. 
Click on the links below to fast-forward to the topics that interest you. 
The WA Commercial Potato Seed Lot Trial has been conducted annually since 1961 (with a short hiatus in the late '70s). It identifies seed-borne diseases impacting potato crops in the region, and helps individual growers diagnose seed-borne issues that occasionally show up in their crop. 

"Have Potato Seed Problems? This Program Can Help" is an article about the seed lot trial. It describes a few of the seed-related problems the trial has helped to identify over the years.
HOW TO PARTICIPATE IN THE TRIAL:  Washington growers can submit samples from commercial seed lots for inclusion in the trial. Sample tags are available at the Washington State Potato Commission office (call 509-765-8845).  
Collect about 200 WHOLE SEED TUBERS (i.e. single drop seed) or a minimum of 50 lbs. The seed tubers should be 2-4 oz.  Please note that CUT SEED, TREATED SEED, SEED TUBERS OVER 6 oz., and SAMPLES WITH TOO FEW TUBERS WILL NOT BE ACCEPTED.

A representative sample is needed. Sampling the first (or last) 200 seed tubers from the truck is not likely to provide a representative sample. If applicable, include a representative amount of rotten tubers. 
Deliver samples to the Potato Research building at the WSU Othello Research Unit (1471 W. Cox Rd.). Or arrange pick up by calling:  South Basin: Tim Waters (509-545-3511); North Basin: Carrie Wohleb (509-707-3510); Westside: Don McMoran (360-428-4270); or you can call: Rudy Garza or Vito Cantu (509-488-3191) at the Potato Research building at the WSU Othello Research Unit.

Pick up dates are usually ONE DAY PRIOR TO THE PLANTING DATES. Seed lots will be planted on March 28, April 11, April 25, and May 9.

WHEN TO SEE THE RESULTS:  Plants in the seed lot trial that show seed-borne disease symptoms or other seed-related problems, like herbicide carryover injury, will be flagged by professional evaluators in June. Everyone is invited to the WSU Potato Field Day on June 22, 2023 to view the seed lots and discuss the results.

The Washington Commercial Potato Seed Lot Trial is led by Dr. Mark Pavek, Professor and Potato Extension and Research Specialist with WSU. The Washington State Potato Commission funds the trial.
POTATO VIRUS Y: PVY is the reason for most potato seed lot downgrades by seed certification agencies. This disease has become increasingly difficult for seed growers to deal with due (mostly) to the rapid spread of recombinant PVY strains (e.g., PVY-N:O, PVY-NTN and PVY-N-Wi) that produce mild symptoms that are difficult to rogue. The potato seed lot trial has helped document the PVY strain shift (from PVY-O to the newer recombinant strains) that has been occurring in North America over the last decade, and it is helping growers and seed inspectors learn to recognize the less obvious symptoms of PVY.
PVY SYMPTOMS:  All of the plants shown above are affected by seed-borne PVY, but symptoms vary depending on the PVY strain and the potato cultivar it infects. A characteristic symptom involves a yellow to light green mottling of leaves, a.k.a. mosaic. The mosaic can be mild (not shown), moderate (A), or severe (B). Some cultivars have a hypersensitive reaction to PVY that results in dark brown necrotic streaks on the leaves (C). Photos by Carrie H. Wohleb, WSU.

Click HERE for more pictures and information about PVY symptoms and diagnosis.
SOME PVY STRAINS CAN CAUSE TUBER SYMPTOMS:  The pictures below show Alturas cv. plants affected by different strains of PVY. Some of the recombinant PVY strains, like PVY-NTN, can cause potato tuber necrotic ringspot disease (PTNRD) in some cultivars. PTNRD results in necrotic rings on the tuber surface that sometimes crack and extend into the tuber flesh. Photos by Carrie H. Wohleb, WSU (leaves) and Bruce Watt, University of Maine, (tuber).
HOW TO MANAGE PVY:  The best thing you can do to minimize PVY in your crop is to start with clean seed. It is important to buy limited generation seed known to have little to no detectable PVY. Get a copy of the health certificate and scrutinize the results from field inspections and testing.  

For more information about PVY, including more management recommendations, read this article "Why Potato Virus Y Needs Your Attention".
HERBICIDE CARRYOVER: Herbicide carryover injury can result when herbicide residues persist in soil, in manure or compost, or in potato seed tubers. The WA Commercial Potato Seed Lot Trial can help to verify cases where herbicide injury originated in the seed, because symptoms show up in both the grower's field and the seed lot trial.
GLYPHOSATE CARRYOVER:  Glyphosate that drifts onto a potato seed crop can accumulate in the tubers and then cause problems the next season. Symptoms vary depending on the concentration of glyphosate residues. Plants may not emerge, or they can be be stunted. Glyphosate tends to cause a proliferation of sprouts. It can also cause some bending and twisting of emerged leaves. Photos by Carrie H. Wohleb, WSU. 
CLOPYRALID CARRYOVER:  Another seed-borne herbicide carryover issue that we have seen involves clopyralid (e.g., Stinger). When clopyralid residues affect seed, the plants show delayed emergence and leaves with a fiddle-neck shape. Photos by Carrie H. Wohleb, WSU. 
NEW SUBSCRIBERS:   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.  

Have a great growing season! 

Questions or comments can be directed to:

Carrie H. Wohleb, Ph.D.
Professor / Potato, Vegetable & Seed Extension Specialist
WSU Extension - Grant County - Columbia Basin

Tel: (509) 707-3510
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