Bulletin number 5, 6/22 – 7/1/20

Welcome to bulletin 5 for the 2020 growing season. Download the spore trapping potato data here and the sugar beet spore trapping data here. Both excel spread sheets require a password to open then. Email us to request access to the data.


The weather in southern Idaho continues to be favorable for late blight, with unseasonably cool temperatures and periods of high humidity and rain. All the weather stations we monitor in S Idaho registered at least two consecutive days (6/29 and 6/30) with over 11hrs of humidity above 80%. In our current late blight model for Idaho, if you have two consecutive days with more than 10 hours of relative humidity (RH) above 80% then there is an elevated risk for late blight. These are know as Critical Humidity Periods (CHP) and all stations registered at least one this past week.

No late blight spores were detected at any of the spore traps this week. However, the two spore traps in the Paul / Rupert area malfunctioned this week resulting in a few days where no sampling occurred. However, with the elevated risk suggested by the CHP model, growers should remain vigilant for late blight symptoms when scouting fields. Growers in the Rupert, Paul, Twin Falls area where crops are at or around row closure should consider including a fungicide which has activity against late blight in their spray programs.

For a list of registered fungicides for control of late blight in southern Idaho see the attached document.

This week Sclerotinia sclerotium (white mold) spores were detected at Rexburg, Tetonia and Parma. Alternaria solani (early blight spores were detected at Aberdeen and American Falls.

Sugar beet

Spores of Erysiphe betae were detected frequently in Parma, Glenns Ferry and to a lesser extent at Kimberly. None were detected at American Falls.