Last week Thursday, reports began coming in from southern Wisconsin of late blight in potato fields. On Monday, the Oneida County UW-Extension received confirmation from University of Wisconsin-Madison that late blight is present in Wisconsin potatoes and tomatoes in several counties, including Oneida County.
This season’s sporadic thunderstorms have created optimum conditions for the spread of the disease, and now that it’s present, home growers should pay careful attention to the health of their plants. UW-Extension is recommending foliar fungicide sprays on all tomato and potato plants to protect them from this lethal disease. Already-infected plants should not be sprayed, but rather removed and burned/dried in the sun, then thrown in regular garbage.
The strain of the disease present in Wisconsin samples is US-23, a quickly reproducing, vibrant type that is moderately resistant to some fungicides. It is critical for potato and tomato growers that plantings are scouted regularly and receive protective fungicides on a weekly basis.
Plantings that have received or will soon receive vine kill treatments should still be protected, because lower stems of potato plants often are still green enough to host the late blight pathogen. This can lead to a wider infestation and contamination of the potato crop. Rain can also wash spores from these plants to nearby healthy plants.
Growers with questions on late blight should call UW-Extension at (715) 365-2750.