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Farm News: State Officials Say Fight Potato Blight Now


Posted: 05.04.2011

Taking care of unwanted spuds now may mean protecting the state from potato blight this year.

Wisconsin Department of Ag officials say all growers and gardeners should destroy piles of discarded potatoes no later then May 20th.  The unwanted spuds could potentially harbor late blight, a fungus that could harm Wisconsin potatoes and tomatoes.
“Two summers ago, many home gardeners and commercial growers in Wisconsin experienced late blight first-hand as they lost their tomatoes to this destructive plant disease while our state’s commercial potato crop was mostly spared,” said Adrian Barta, DATCP plant pest and disease specialist. “In 2010, the disease was not as widespread with isolated cases reported in 12 counties affecting potatoes and tomatoes for both gardeners and commercial growers.”
While the fungus is not believed to overwinter in Wisconsin’s soil, it can survive on live plant material that survives the winter, in potatoes left in cull piles or on infected plants and tomato fruits that were put into compost heaps or bins, Barta explained.
Wind can move late blight spores from infected gardens and fields. There is a risk of spreading the disease to this year’s crop if any infected potatoes remain in mismanaged cull piles. This is why the state agriculture department requires that potato growers destroy piles of unwanted or waste potatoes by May 20. The unwanted potatoes can be spread on cropland then plowed or disked into the soil, taken to a licensed landfill or fed to livestock as long as the potatoes are completely eaten by the deadline. Other disposal methods must be approved by the department.
“Our staff will be checking for cull piles as we do our field work. We urge growers to take the initiative and handle their cull piles properly,” Barta said.
Wisconsin potato growers can also protect against late blight by scouting fields for volunteer potato plants and either removing the plants or applying herbicides.
Home gardeners and smaller growers should also take precautions during the upcoming growing season.
“Watch for volunteer tomato or potato plants in your garden and compost heap. Pull them out and place them in a plastic bag then put the bag out with the trash,” Barta said. “For spring planting, purchase healthy looking tomato plants and select varieties that are late blight resistant. If you raise your tomatoes from seed, there is no risk of introducing late blight into your garden.”
Some gardeners have discovered that potatoes they saved last year with the intention of planting this spring are infected with late blight.
“If you normally grow potatoes, do not reuse last year’s seed potatoes because the seed pieces may be carrying late blight. Buy new certified potato seed from a reliable supplier,” Barta advised. 
Compost bins or piles also need extra attention to prevent the spread of late blight.
“Compost bins or piles may harbor late blight because they don’t generate enough heat to kill the pathogen,” Barta explained. “Destroy any sprouting plants or green plants that you find. Your neighbors and farmers will appreciate your efforts to prevent the spread of this disease.” 
You can find more information on late blight at If you suspect late blight on potatoes or tomatoes, please contact your county’s Cooperative Extension office or the University of Wisconsin Plant Disease Diagnostic Clinic,
For more information on regulations governing cull piles and late blight, call Adrian Barta at (608) 224-4592 or email

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