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Root rot control possibilities for South Texas cotton

CORPUS CHRISTI, Texas - Cotton farmers soon may have an economical and effective means of controlling root rot.

John Matocha, Texas A&M professor of soils and plant nutrition at the Corpus Christi Research and Extension Center, says a chemical fungicide applied in the seed furrow and encapsulated onto slow release nitrogen starter fertilizer “has shown substantial reductions in root rot damage.”

Root rot causes substantial lint yield losses on many Southwest cotton fields. “This is one of the major diseases of cotton in high pH, calcerous soils in the Southwest,” Matocha said. “In addition to cotton, more than 2,000 species of wild and cultivated plants are susceptible to infection from this soil fungus.

“The unique nature of the pathogen (Phymatotrichopsis omnivora) allows it to survive for an extremely long time.”

Matocha said the advent of sprinkler irrigation in the Texas Coastal Bend area “has aggravated the root rot problem, especially where numerous small irrigation applications are made.”

He said previous control practices have proven either economically infeasible or ineffective. His previous research shows that improving cotton plant nutrition may delay and reduce severity of the disease. The combination of time-released fungicide and improving trace element nutrition may improve control, he said.

His research has “suggested a strong association between topographical elevations, particle size distribution and soils either supportive or suppressive of the pathogen.”

He’s looked at nutrient deficiencies, especially iron, as well as magnesium, zinc and nickel and found that these “are usually in short supply in problem soils.”

Matocha used aerial infrared photography and visual inspections to document root rot infected soils producing cotton and also the nutritional status of grain sorghum crops on identical soils. He worked with both greenhouse and field plots to evaluate the effects of organic, biological, cultural, and chemical control methods on the disease.

“Most promising for suppression of root rot on cotton has been a non-commercial iron-enriched Amaranthus material, a mined Florida iron material, a synthetic iron chelate and Propiconazole, a fungicide,” Matocha said.

He also evaluated Cyproconazole and Iprodione fungicides.

He said iron chelate materials applied in the seed row reduced plant mortality from 61 percent for untreated to 36 percent for the iron-treated plot. Controlled-release Propiconazole, “had the greatest effect with only 10 percent plant mortality. Cyproconazole appeared to perform similarly.”

Matocha said his work, along with cooperation from industry, indicates that formulating a granular sterol-inhibiting fungicide into time-release granules, applied in the seed furrow, offers significant promise in reducing root rot infection in cotton.

He said that after completing small plot work with the system and determining the most effective fungicide rates, the best carrier granules, and the best release rates for the fungicide, he can use GPS technology to identify and treat only the diseased areas of a cotton field.

“So far, limited external funding has slowed process in selecting a fungicide and fine tuning chemical release rates,” He said.

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