The tool for estimating potential survival of potato volunteers in Michigan and Wisconsin is now available on our new Potato and Sugar Beet Pathology website. Epidemics of potato late blightare initiated from mycelium of Phytophthora infestans. This organism survives between successive growing seasons by overwintering in infected potato tubers intended for seed, or as volunteer tubers that are left in fields at harvest, or within discarded cull and rock piles.
It is difficult to estimate the probability that infected potato stems will emerge from an infected tuber and several factors can influence the fate of the infected tuber, temperature being one of the most important. Over the past five years of monitoring, it has been recorded that over-winter soil thermal conditions have been conducive for the survival of volunteer potatoes, which may act as potential sources of inoculum in the spring.
By clicking on the help page link, you can access additional information about volunteer survival, including the following.
Studies at Michigan State University have shown that tubers of most cultivars appear to breakdown after exposure to 27 degrees Fahrenheit for about one day. We have developed a model that predicts the likelihood of volunteer survival over the winter based on soil temperatures between Nov. 1 and March 31, summarized below:
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Hours below 27 F at:
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Risk
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2-inch depth
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4-inch depth
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> 120
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> 120
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Low
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> 120
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< 120
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Moderate
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< 120
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< 120
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High
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Conclusion
Most regions in Michigan experienced soil thermal conditions that placed them in the high-risk category for volunteer survival (Fig. 1). Some areas did experience extended periods of cold temperatures this winter and are predicted to have low or moderate risk. However, these locations are generally surrounded by other high risk areas. Therefore, growers throughout the state should be implementing their integrated pest management (IPM) scouting programs early in 2019 and considering volunteer elimination programs in adjacent crops and non-potato crops if herbicides are registered.