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Late blight found in Pierce County

Late blight can destroy tomato and potato plants in seven to 10 days, according to the UW-Extension office. The fungus-like water mold can decimate the plants if weather conditions are cool and wet. Photo courtesy of UW-Extension program

Late blight, a fungus that can kill tomato and potato plants, has been confirmed in Pierce County, according to the Pierce County UW-Extension Program.

Horticulture Educator Diana Alfuth said the fungus was found after a River Falls commercial farmer sent in a sample to the Plant Disease Diagnostics Clinic in Madison.

Late blight is a fungus like water mold that 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 said.

Late blight is transferred by the spores blowing in the wind, thriving under cold and wet conditions. Alfuth said this summer has been just that and said it reminds her of 2015, when her own tomato plants contracted the blight, decimating them.

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

Alfuth said late blight was what caused the great potato famine in Ireland in the 1800's, but the strain involving tomatoes is more common in Pierce County than the potato strain.

The best advice Alfuth can give homeowners and commercial farmers 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 said.

As a homeowner, Alfuth suggests a copper based fungicide to spray on those plants before the strain begins to take a hold. Alfuth said 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 they will test the samples for free.

The clinic's website lays out the best way to send in samples: https://pddc.wisc.edu/.

Alfuth said she's heard of late blight in some places in North Dakota and Minnesota, but said that Waukesha County also has traces of it. However, Alfuth said this is just the beginning and believes more confirmations will be coming, but couldn't say if 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," Alfuth said.

The Pierce County Extension office is located in Ellsworth and is open from 8:30 a.m. to 4:30 p.m. Monday through Friday at 412 W. Kinne St.

Matthew Lambert

Matthew Lambert joined the Pierce County Herald and River Falls Journal in December 2016 covering government, school board, and writing features about the community. He is a graduate of Winona State University with a Bachelor's degree in Journalism. 

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