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New Mexico State University

New Mexico State University

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Humid Days Mean Time is Ripe for Powdery Mildew in Chile

LAS CRUCES -- After recent stretches of humid weather, chile growers should protect their crops from a disease called powdery mildew, a New Mexico State University plant pathologist said.

In eastern and southwestern New Mexico, stormy weather at the end of June created ideal conditions for the disease, said Natalie Goldberg with NMSU's Cooperative Extension Service.

The fungal disease produces a white, powdery growth on the underside of leaves.

"In chile, powdery mildew will cause the leaves to curl up and eventually fall from the plant," she said. "The disease can prematurely defoliate a chile plant, which can sunburn fruit."

Although it was once uncommon in New Mexico, powdery mildew has caused economic losses the last two years, she said.

"The ideal conditions for the disease are four to five days where the maximum humidity is 90 to 100 percent and the minimum humidity never falls below 35 percent," Goldberg said.

From June 27-30, that was the case in Clovis, Artesia and the Mesilla Valley. Deming probably had similar conditions but since it has no weather monitoring station, it's impossible to know for sure, Goldberg said.

Because the disease cannot be cured once plants are infected, growers should protect their crops after humid weather conditions.

"The best approach is preventive sprays with sulfur products, which are approved for use on organically grown produce and won't cause problems for growers who are not using other types of chemicals," Goldberg said.

The treatments should be applied immediately after a stretch of high humidity, before powdery mildew appears.

"The infection usually starts on the bottom part of the plant, so it's essential to get thorough coverage of the plant, from top to bottom, including the undersides of the leaves," Goldberg said.

Growers should continue to monitor humidity levels as New Mexico enters the traditional rainy months of July and August, because powdery mildew can attack chile plants of all ages and varieties, she said.