Late Blight Found in Wisconsin

Published online: Aug 09, 2017 Articles Matthew Lambert
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Late blight, a fungus-caused disease that can kill tomato and potato plants, has been confirmed in Pierce County, Wis., according to University of Wisconsin Extension.

Pierce County horticulture educator Diana Alfuth says the fungus was found after a commercial farmer in River Falls, Wis., sent in a sample to the Plant Disease Diagnostics Clinic in Madison.

The fungus is similar to water mold and can make tomato fruits and potato tubers inedible.

“If you get it in your garden, it can wipe out your stuff pretty darn quick,” Alfuth says.

Late blight is transferred when its spores blow in the wind, and it thrives under cold and wet conditions. Alfuth says this summer in Wisconsin has been just that and said it reminds her of 2015, when her own tomato plants contracted late blight, decimating them.

On tomatoes, late blight appears as sunken, golden to chocolate brown circles that are distinct and firm. On potato tubers, it appears as a reddish-brown discoloration under the skin.

Alfuth says late blight was what caused the great potato famine in Ireland in 19th century, but the strain involving tomatoes is more common in Pierce County than the potato strain. The best advice Alfuth can give homeowners and commercial growers is simple: Start treating now.

“If you’re a commercial grower, you need to be treating your stuff now, before it takes a hold in your patch,” Alfuth says.

As a homeowner, Alfuth suggests a copper-based fungicide to spray on tomato and potato plants before the disease begins to take hold. Alfuth says she will be spraying her plants as soon as possible.

Alfuth suggests that people who are unsure can send samples of a tomato or potato to the Plant Disease Diagnostic Clinic in Madison, where the staff will test the samples for free. The clinic’s website, accessible here, lays out the best way to send in samples. 

Alfuth says she’s heard of late blight in some places in North Dakota and Minnesota, but that Waukesha County, Wis., also has also seen traces of it this year. However, Alfuth says this is just the beginning and believes more confirmations will be coming, but couldn’t say whether surrounding counties St. Croix, Dunn or Polk had any traces.

“It’s just starting. … I’m sure the number of confirmations will begin to balloon,” she says.

 

Source: River Falls Journal