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New Mexico State University

New Mexico State University

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Chile Growers Brace for Another Disease

LAS CRUCES - A light powder on the leaves of chile plants in southern New Mexico fields is the calling card for powdery mildew, another grower's headache in an already disease plagued season, said a New Mexico State University plant pathologist.

"Powdery mildew is caused by a fungus that attacked New Mexico chile last September causing minor damage," said Natalie Goldberg, with NMSU's Cooperative Extension Service. "Now, the fungus is back a month earlier and could cause much more damage because it defoliates chile fields at a time when the fruit needs the shade of the leaves."

"When the disease occurs late in the season, it's a welcome sight for growers because it can serve as a good defoliant for red chile harvest," Goldberg said. "However, if severe infections occur earlier, the disease may result in heavy yield losses due to sunscald, which causes indentations and discoloration, making it unmarketable."

The fungus that causes powdery mildew predominately infects the leaves, but it can occasionally be found attacking the fruit. The disease is most severe on older leaves just prior to fruit set, but can occur anytime throughout the season if conditions are favorable.

The primary symptom of the disease is a white, powdery, fungal growth that covers the lower leaf surface. The upper leaf surface of infected leaves may show a yellow or brownish discoloration and, in some cases, the fungus may actually appear on the upper leaf surface. Edges of infected leaves eventually roll upward exposing the fungus.

The disease thrives in warm weather and high humidity. "The early appearance of the fungus this year is probably related to the high disease presence last year and the mild winter conditions," she said.

The fungus infects a variety of plants, including, cotton, onion, tomatoes, ornamentals and weeds. Between chile crops, the fungus survives on other plants.

The fungus' persistence means sanitation practices such as destroying infected crop debris and controlling weeds in and around chile fields are not always enough to control the disease, Goldberg said. In addition, most chile varieties have a low tolerance to this fungus.

"Because of these factors, control is usually dependent on chemical sprays," she said. "Chemicals registered for use on peppers for the control of powdery mildew contain sulfur, and some can be used on organically grown chile. Sprays are most effective when disease detection is early and application coverage is thorough."

For more information about powdery mildew control, contact your county Extension office.