Fungicides not effective in treating hardlock in upper Southeast cotton

Researchers in the upper Southeast have not been able to duplicate the success of others farther south in treating hardlock with fungicides, says a North Carolina State University plant pathologist.

Researchers in Florida created a stir several years ago when they reported control of hardlock with fungicides.

“So far, we’ve not been able to demonstrate a reduction in hardlock with fungicides,” North Carolina State University research assistant professor and plant pathologist told the recent Southeast Cotton Conference in Rocky Mount, N.C.

Koenning presented research from North Carolina as well South Carolina at the annual conference sponsored by Southeast Farm Press.

Hardlock occurs when lint in the cotton boll fails to fluff enough to be picked. When picker spindles hit the “hard” bolls, the bolls fall apart and drop to the ground. Hardlock is the reason, researchers say, that we grow two bale cotton and harvest only a bale and a half.

Researchers in Florida theorized that the fungus Fusarium verticillioides is a cause. Damage from piercing-sucking insects is another cause.

Hardlock seriously affects yields in the Southeast, but it’s “highly variable from year to year and that’s been the problem with research,” Koenning says.

In South Carolina, Clemson University Extension plant pathologist John Mueller looked at nine different fungicides, comparing ratings and timing at two locations with two varieties.

Using weekly sprays after first bloom, with different timings and applications, Mueller found no difference in cotton yields. On one of the untreated checks, he saw a decrease in yield. “Once in a while you might get a fungicide application that might benefit you,” Koenning said, in reporting the research, “but we saw virtually no difference regardless of the variety used.”

In North Carolina, using Delta and Pine Land 555 and 451, spraying at cracked-boll stage, Koenning found no significant difference between fungicide sprays and untreated checks.

“It looks like we’re getting an increase in yield with more sprays, but when you go from three sprays to four sprays, it drops down again,” Koenning says.

Researchers found a trend for higher leaf area with fungicide applications, Koenning says. “More than likely, we’re controlling some of the miscellaneous cotton foliar diseases, the cotton is staying greener longer, but this isn’t necessarily a good thing. More leaf area might interfere with defoliation.

“By controlling some of these miscellaneous fungi, we may be delaying maturity,” Koenning says.

The bottom line is, researchers in the upper Southeast haven’t found a meaningful difference in their research with fungicides to control hardlock. “Reduction in hardlock by the use of fungicides is hard to demonstrate,” Koenning says.

The research will continue in 2005.

e-mail: [email protected]

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