Hot, Humid Weather Favors Chile Disease

Date:  July 25, 1997
Editor: D'Lyn Ford  (505) 646-6528, dlford@nmsu.edu

LAS CRUCES -- High temperatures and humidity in southern New Mexico could spell problems for chile with powdery mildew, a yield-reducing disease.

"We expect to start seeing this disease in Dona Ana County fields," said Natalie Goldberg, plant pathologist with New Mexico State University's Cooperative Extension Service. "We've already had some samples brought in from Luna County, so it's probably just a matter of time for this area."

Powdery mildew, caused by a fungus, attacks the lower leaves of chile plants first. The disease causes a small lesion on the upper sides of leaves and a grayish powdery growth on the undersides. It gradually works its way up the plant as the disease develops.

"If powdery mildew hits fairly early in the season, you get a lot of leaf curling that exposes fruit to direct sunlight, which leads to sunburned pods and yield losses," Goldberg said. "It also can lead to defoliation, which is going to cut yield."

If the disease strikes during red chile harvest in September, losses are much smaller.

The only option for treating powdery mildew is preventive spraying with a registered sulfur product, Goldberg said. Spraying must begin at the first signs of the disease and reach the undersides of leaves. If rain washes it off, the application must be repeated to be effective.

"Powdery mildew is difficult to treat because you can't reach the lower part of the plant and the undersides of leaves with aerial spraying," Goldberg said. "Once the plants are good-sized, you have a hard time getting into the fields with ground rigs."

Until a few years ago, powdery mildew on chile was fairly rare in New Mexico, but the disease now seems entrenched, Goldberg said.

"Unfortunately this disease can survive on a wide range of host plants," she said. "I think it's probably here to stay."

The disease affects lettuce, many weeds, solanaceous plants such as tomatoes and ornamental plants, particularly native ones.