New website for estimating potential survival of potato volunteers in Michigan

Several interacting variables are causing survival of potato volunteers to be an increasing problem in Michigan. This new website will help with control.

Volunteer pageA new website for estimating potential survival of potato volunteers in Michigan is now available. Several interacting variables including meteorological factors such as climatic change and increasing tolerance of Phytophthora infestans to colder temperatures represent a serious situation for the potato and vegetable industry in Michigan. From 1950 to present, climatic conditions in Michigan have been becoming steadily more conducive for the initiation and development of potato and tomato late blight epidemics. At the same time, as P. infestans populations are developing, increasing tolerance to colder temperatures, winters in Michigan are becoming warmer, which favors over winter survival of potatoes left behind in the field after harvest (volunteer potatoes) and waste (cull) potatoes.

Epidemics of potato late blight are initiated from mycelium of P. infestans, which survives between successive growing seasons by overwintering in infected potato tubers intended for seed, as volunteer tubers left in fields at harvest, or within discarded cull and rock piles. With the recent trend for warmer winters, more volunteers and cull pile potatoes are surviving the winter and acting as sources of inoculum in the spring. 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.

Michigan winter soil temperatures from the soil surface down to a depth of 45 cm have been monitored for several years and show that the soil at 15, 30 and 45 cm depths does not experience freezing for extensive periods at any of the locations monitored between the coldest winter months in Michigan (the lowest was between 27 and 29°F for five days at the Southwest Michigan Research and Extension Center). We have now established that meristematic tuber tissue breaks down after exposure to 27°F for about 120 hours (five days) in several commonly grown potato varieties, as does the pathogen that causes late blight (P. infestans).

What is volunteer survival?

Potatoes that are left in the field at harvest are known as volunteer potatoes. In areas where winter soil temperatures are not cold enough to kill tubers left in the field, they can survive the winter and become a serious weed problem the following spring (for more information, see the effects of climate change on the overwinter survival of volunteer potatoes in Michigan). In addition, volunteer potatoes that survive the winter can harbor pests and diseases. Epidemics of potato late blight can be initiated from mycelium of Phytophthora infestans, which survives over winter in infected volunteer potatoes.

Studies at MSU have shown that tubers of most cultivars appear to breakdown after exposure to 27°F for about one day. We have developed a model that predicts the likelihood of tuber survival over the winter based on soil temperatures at 2 and 4 inches between November 1 and March 31. If tubers were exposed to temperatures below 27°F for more than 120 hours between November 1 and March 31 at 4- and 2-inch depth, then the risk of tuber survival is considered low (indicated by a green marker pin). If tubers were exposed to temperatures below 27°F for less than 120 hours at 4-inch depth and greater than 120 hours at 2-inch depth, then there was a moderate risk of tuber survival (indicated by a yellow marker pin). If tubers were exposed to temperatures below 27°F for less than 120 hours at 4-inch depth and less than 120 hours at 2-inch depth, then there was a high risk of tuber survival (indicated by an orange marker pin).

This winter, all regions experienced soil thermal conditions that placed them in the high risk category for volunteer survival. Only Stephenson, Mich., (Menominee County) was at low risk, and Hastings, Mich., (Barry County), had moderate risk. This situation should alert potato growers to the high risk of potato volunteers surviving the winter and all growers should, therefore, be implementing their integrated pest management scouting programs early in 2012 and considering volunteer elimination programs in adjacent, non-potato crops if herbicides are registered.

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