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Excessive Mid-South Temps Affect Crop

By Carroll Smith
Senior Writer

Hot. Hotter. Hottest. A heat wave in the Mid-South began in June and continued to accelerate through July and into August. The obvious question on everyone’s mind was, “What will these high temperatures do to the cotton crop?”

Derrick Oosterhuis, a Distinguished Professor of Crop Physiology with the University of Arkansas, says that although cotton originates from hot climates, it doesn’t necessarily yield best at excessively high temperatures.

“The ideal range for cotton production is from 68 to 86 degrees,” Oosterhuis says. “Temperatures above 90 to 95 degrees are not optimum for growth.

“Over the years in the Delta region, we’ve shown a correlation does exist between high temperatures (95 degrees or above) in July and August during the boll development stage and low yields,” he adds.

Arkansas & Mississippi
Specialists Weigh In

Tom Barber, University of Arkansas Extension cotton specialist, says high temperatures can, and, in most cases, will cause fruit shed.

“There’s nothing we can do about fruit shed caused by the heat, but the crop may have to be managed like a later maturing crop,” Barber says. “Whatever positions are blooming now during these high temperatures probably will not pollinate due to lower than optimal pollen production, resulting in poorly fertilized blooms. When this happens, the bloom dries down, and the young boll falls off or sheds. High daytime temperatures can cause this phenomenon, but the high nighttime temperatures are especially detrimental to bloom pollination.”

Barber notes that there is a good chance that “whip” may occur. Whip looks like a twig or a bare stalk on top of the plant. Therefore, when the crop is defoliated, there is not any cotton in the top.

“Defoliating this crop will be tricky because of the extreme heat,” he adds. “Some products may work too quickly and stick leaves. Growers should choose products and rates wisely based on daily temperatures.”

In Mississippi, Extension cotton specialist Darrin Dodds echoes Barber’s concerns.

“We’re seeing some shed out of the top and may see some misshapen bolls because the plant didn’t pollinate correctly during the persistently high daytime and nighttime temperatures,” he says. “Time will tell, but it will be a while before we know for sure what the ultimate effects of the high temperatures will be on Mid-South cotton in the 2010 season.”

The Arkansas professor notes that high temperatures have a two-fold effect on cotton. First, they decrease photosynthesis, which shortens the supply of carbohydrates, or sugars, needed for boll development and fiber development on the seed. Also, in the individual flowers, high temperatures affect pollen tube growth down to the seed, which affects fertilization and results in a reduced seed number.

“Reduced seed number means reduced amount of fiber, which means reduced yield,” Oosterhuis says.

Active Ingredient Looks Promising

The good news is that studies conducted by Oosterhuis have shown that certain plant growth regulators that contain the active ingredient 1-MCP can alleviate plant stress associated with high temperatures. 1-MCP is a chemical that blocks the plant’s ethylene sites. Ethylene is a stress hormone produced by the plant when the plant is stressed. This hormone can prompt senescence, early maturity and boll shed. But if the ethylene sites are blocked, then the plant can’t recognize this stress hormone, and the plant grows as if it was not stressed.

“This active ingredient helps the plant hold on to young bolls and also promotes pollen tube growth in the flower,” Oosterhuis explains. “Current formulations last for about four days. If the temperatures stay up, then we will make another application.”

EPA has approved 1-MCP for applications in cotton, and commercial products with this technology should soon be available to producers.

Contact Carroll Smith at (901) 767-4020 or csmith@onegrower.com.

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