High risk of potato volunteers due to warm overwinter soil temperatures

Due to a combination of a warm 2023-2024 winter season, and a heavy snowpack during the few weeks when air temperatures did drop into the single digits, soil temperatures in central Wisconsin may not have reached temperatures cold enough to kill potato tubers left in the field after harvest. Normally, 4-inch soil temperatures below 27F for 120 hours are sufficient to kill off any volunteer potatoes remaining in the field.

However, based on soil temperature data retrieved from the Hancock weather station, these low temperatures were not reached this winter for any amount of time, so the risk of potato volunteers is very high in the coming 2024 growing season. Volunteer potatoes bring increased risk of serious diseases such as late blight since they typically appear in fields and margins that are not being managed for potato in the current growing season so do not receive preventive fungicide applications.

Soil temperature record from the Hancock weather station, winter 2023-2024. Soil did not cool below 27 degrees Fahrenheit at any time during the winter.

The Rhinelander station, which is 100 miles farther north than the Hancock station, did experience colder temperatures, but these again were not sufficient to kill volunteers. 2-inch soil temperatures fell below 27F for only 26 total hours, which is far less than the 120 hours required for a good potato volunteer kill.

Soil temperature record from the Rhinelander weather station, winter 2023-2024. Soil cooled below 27 degrees Fahrenheit only at a 2-inch depth and only for 26 hours over the winter.