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New Mexico State University

New Mexico State University

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No New Diseases Detected in New Mexico's Chile

LAS CRUCES -- Diseases continue to eat away at New Mexico's ailing chile crop, but laboratory tests show no new viruses, said a New Mexico State University plant pathologist.

"Everything we've seen out there in the fields, we've had before," said Natalie Goldberg with NMSU's Cooperative Extension Service. "We might have problems at a worse level, but so far there isn't anything new."

Samples from chile fields in Hatch, Rincon, Mesilla, Las Cruces and the Uvas Valley tested positive for the beet curly top virus, which caused major losses in 1995, Goldberg said. The specimens were sent to an Indiana laboratory that screened them for 15 common pepper viruses.

"More than 98 percent of the samples came back infected with beet curly top," Goldberg said. "That was the only viral disease detected in those plants."

An insect called the beet leafhopper spreads the curly top virus. Once it has been transmitted to plants, there is no cure.

"A virus is not a living organism," Goldberg explained. "Essentially, it's made up of RNA or DNA molecules that contain genetic code.

"Once a virus gets inside a plant, the plant starts to replicate the viral RNA or DNA at the expense of replicating itself. That causes abnormalities and weird growth."

Chile plants infected with curly top develop yellow, curled leaves and stiff, thickened stems that break with a snap. Diseased plants may produce a few dull, wrinkled peppers that ripen prematurely.

Farmers can sometimes compensate for curly top damage by planting a thick stand and thinning out diseased plants. This year, cold night temperatures and high winds interfered with germination and growth, leaving fields with weak stands and large skipped sections.

Curly top is one of the most common viruses seen in New Mexico's chile. Researchers expected problems this year after mild winter weather allowed beet leafhopper numbers to build.

In addition to curly top, alfalfa mosaic, cucumber mosaic and tomato spotted wilt viruses can cause damage, Goldberg said. Because little can be done once viral diseases strike, they can be particularly devastating.

Aside from viruses, pepper plants suffer from plenty of other problems.

"Chile is a good host for diseases," Goldberg said. "We have numerous fungi, bacteria, viruses and nematodes. When you add them all up, probably over 100 different things can happen to chile. They don't all necessarily happen in New Mexico, but it is a susceptible plant for problems."

Perhaps the best-known chile disease kills mature chile plants mid- to late season, claiming up to 25 percent of the crop. Phytophthora root rot, commonly known as chile wilt, is caused by a fungus in the soil.

"Phytophthora is basically a water mold. It likes excessive soil moisture," Goldberg said. "Heavy summer rains help to create conditions that are favorable for this disease."

Poorly drained fields with heavy, clay soils are most susceptible to problems with Phytophthora root rot. Crop rotation and careful irrigation can help suppress the disease.

Powdery mildew, another fungal disease, is likely to strike again this season. The fungus causes plant leaves to curl, defoliating the plant and exposing chile pods to sunburn injury. Powdery mildew has reduced chile yields in New Mexico since 1995.

Conditions this year also favor Verticillium wilt, a fungal disease that causes yellowing, slow wilting and death in chile and many other plants. Cool spring temperatures and high soil moisture favor infection. Although plants are infected early in the season, they typically do not show symptoms until later in the summer.

This year's weather kept chile plants from germinating and growing normally, making them more susceptible to diseases of all kinds, Goldberg said.

"Unfortunately, it's not a good year to be a chile plant or a chile farmer," she said. "We hope this combination of weather, insect and disease problems is just a one-year event."