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Researchers Test Alternatives To Pesticides For Potato Disease

Farmers who don”t want to combat potato early dying disease with pesticides may soon have another way to protect their crops, according to a University of Wisconsin-Madison researcher. However, she cautions that it will be difficult to find alternative practices that are as effective as fumigation.

For years, growers have fumigated their fields with pesticides to control early dying, a chronic problem in Wisconsin. Growers now treat almost 40 percent of the state”s potato acreage. If left untreated, early dying causes the leaves of the plant to wilt, and ultimately the plant dies. If a field is infected, farmers will lose a significant part of their crop.

Two soil-dwelling organisms, a fungus and a microscopic, worm-like creature called a nematode, cause the disease. Either the fungus or the nematode by itself can invade a potato plant and cause disease, but when they occur together the levels of the disease increase more than expected, according to Ann MacGuidwin, a nematologist with the College of Agricultural and Life Sciences. The pesticides that control nematodes are expensive, have the potential to pollute groundwater, and may kill beneficial soil organisms, so finding an alternative practice is important, she says. She spoke recently at the UW-Extension and Wisconsin Potato and Vegetable Growers Association Conference in Stevens Point.

“Potato growers in Wisconsin care about the environment, which means thinking about how the crop is grown,” MacGuidwin says. “Wisconsin”s potato industry is taking steps to use cleaner practices for controlling insects and many diseases, but there are no alternatives to fumigation at this time. The industry is eager for new technologies and very supportive of this research.”

In order to control pest nematodes, MacGuidwin is investigating two methods of adding organic material to the soil. The first is to plant cover crops that are toxic to nematodes, such as rapeseed and mustard. Cover crops are typically planted in the late summer or fall, after the main crop is harvested, and allowed to sit through the winter. The second is to feed the entire soil community by applying nutrient-rich paper mill sludge to the fields, which may increase the numbers of the nematode”s natural predators.

So far, MacGuidwin”s theories have worked in the lab, but have not held up as well in the field. At best, these techniques achieved 80 percent of the yield that fumigation gives when there is a high level of disease. “Finding the answer won”t be as simple as we hoped,” she explains. “A field”s ecosystem has a lot of uncertainty like weather and the biological community of the soil. We”re trying to find the right combination of cover crops and organic matter, but it”s hard to replace pesticides because they give predictable and repeatable results.”

Next year, MacGuidwin intends to address some of the uncertainty by analyzing commercial fields. “The whole industry is the experiment, with each farm a replicate,” she says. “We want to build research models based on real farm conditions and experiences. Early dying starts in potato roots so it”s important to find out everything we can about the range of soil conditions and creatures we might use to stop the disease.”