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Potato farmers fight pests with hot mustard

Chinese hot mustard, like horseradish and habanero, is best consumed in small portions.

That’s part of the thinking behind efforts by many Mid-Columbia farmers, particularly potato growers, to raise fields of mustard between crops. The mustard is grown from August to late fall and can reach 5 to 7 feet tall before it’s chopped and tilled.

The chopped and buried mustard plants release chemicals that kill root-knot, root-lesion and stubby-root nematodes – all enemies of Mid-Columbia potatoes.

“The chemicals in the mustard plant are the same chemicals as the mustard seed,” said Andy McGuire, agriculture systems educator for the Washington State University Extension Office in Ephrata. Mustard seed, when cracked and ground, is used to make the hot mustard offered at many Chinese restaurants. In a sense, the pesky nematodes are bathed in the sinus-searing condiment. “It gets into the water they’re living in and kills them,” McGuire said.

Mustard also fights soil-borne fungal pathogens such as verticillium wilt.

Green manure such as mustard also can increase water filtration in the soil and reduce wind erosion – both reasons farmer Dale Gies began using mustard as a cover crop about 15 years ago. He soon found it also killed nematodes and fungal pathogens.

“This one really fit the bill,” he said.

Rick Boydston, a weed scientist with the U.S. Department of Agriculture’s Agricultural Research Service in Prosser, has worked with mustard as a pest and weed controller for more than a decade.

While tilled mustard kills nematodes and fungal pathogens, Boydston said the growing plant suppresses weed growth as well. Tilled mustard, acting as a bio-fumigant, also has the potential to inhibit weed germination.

However, he said, “If it’s suppressing weeds, it can suppress your crop.”

Boydston said the key to reducing weed germination but not affecting the potato crop is timing it so the chemicals released by the mustard diminish by the time potato planting begins in the spring. The large size of the potato tubers also helps protect them from the mustard chemicals, he said.

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