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New Mexico State University

New Mexico State University

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Rating System Helps Cotton Growers Figure Risk of Seedling Diseases

LAS CRUCES -- New Mexico's cotton growers can use a rating system from the National Cotton Council to figure their risk of yield-lowering seedling diseases and decide whether fungicides are needed at planting.

"Cotton growers in wetter climates use fungicides every year to prevent seedling diseases, but in New Mexico we only have problems in certain years, and the problem for us is predicting which years fungicide treatments at planting will pay off," said Natalie Goldberg, plant pathologist with New Mexico State University's Cooperative Extension Service.

Seedling diseases are caused by fungi that kill young plants, leaving large skipped sections in the field. Though the disease occurs sporadically in New Mexico, growers nationwide lost an estimated $1.25 billion to seedling diseases from 1992 to 1996, Goldberg said.

If seedling disease damage is severe, cotton growers must replant, losing time and money. However, applying fungicides in years when they are unnecessary adds to production costs.

The National Cotton Council's Beltwide Program Committee for Cotton Seedling Disease Education has developed a rating scale to help growers decide whether they need to apply preventive fungicides at planting, Goldberg said.

"The two most important factors in the rating system deal with temperature and moisture, because the organisms that cause seedling diseases are triggered by cool, moist conditions," she said.

To figure their risk of seedling diseases, growers begin by calculating soil temperature -- based on a three-day average at a 6- to 8-inch depth -- and checking the National Weather Service's five-day forecast for air temperature and chance of precipitation, Goldberg said.

"For example, if you're in a situation where soil and air temperatures are below the upper 60s and you have a greater than 50 percent chance of rain, you're at a high risk for seedling diseases," she said.

Other risk factors for seedling diseases include seed quality, field history, tillage practices, seeding rate and insecticide or nematicide application.

Growers add up their points from seven questions on the weighted system. A total of 13 points or more means a high risk of seedling diseases.

For a copy of the rating system, contact Goldberg or Shane Ball, Extension agronomist, at (505) 646-1621.