Aug 16, 2017 - MB Potato Disease REPORT #10-B Supplement
Dr. Vikram Bisht
Potato & Horticultural Crops,
This morning, August 16, late blight was reported from southern Manitoba, Rural municipality of Stanley. In regions of high risk, anti-sporulant and translaminar fungicides should be considered.
The weather conditions have generally been dry and warm (Fig 1). However, micro-climate in irrigated fields could be conducive to late blight sporulation in wind protected areas and areas where fungicide coverage is difficult due to terrain or physical barriers. Critical scouting is important, since DSVs (late blight risk values) have exceeded the critical value of 18 in all of Manitoba. Rain showers forecast for the 15th evening, 16th and 17th of Aug increase the risk.
Fig 1. The precipitation continues to be below normal in most of the potato growing areas in MB.
Late blight was confirmed in commercial potatoes on August 14 in Portage County, Wisconsin. The disease was detected in a few fields at low to moderate levels. All of the WI tomato late blight isolates been genotyped as US-23. In North Dakota no additional late blight has been reported since the last report on Thursday August 10.
Early blight is becoming more prevalent as the season progresses. Incidence on RB is still low. In a couple of irrigated fields Sclerotinia stem rot was seen in plants which have lodged; the disease level is very low and does not warrant any sclerotinia targeted fungicide application.