PRODUCTION

Managing Heat-Stressed Cotton

For Mid-South cotton, this seems to be the year of the four-bract square caused by extremely hot temperatures. Another strange growth pattern attributed to excessive heat on young cotton is the appearance of more vegetative branches than usual. Some of them are even growing above the fruiting branches.

Why are there more four-bract squares this year? Chris Main, Tennessee Extension cotton specialist, says most affected cotton was planted from May 10-25 and experienced high temperatures in the upper 90s and low temperatures in the upper 70s for two and a half weeks during the first part of June.

“Microscopic squares begin to form as early as the two-leaf stage,” he says. “Any stress experienced during this period, such as temperatures, thrips or drought, can cause malformed squares. The last year that we had higher-than-average numbers of four-bract squares was 2007.”

Game Plan Following Square Shed

One problem with this type of malformity is that the fourth bract doesn’t allow the square to seal correctly, making it vulnerable to thrips or plant bugs. Typically, a four-bract square eventually aborts.

Darrin Dodds, Mississippi Extension cotton specialist, has seen as much as 65 percent four-bract squares on some varieties that were planted this year.

“That’s awful,” he says. “Four-bract squares can complicate the management of the crop. Once the four-bract squares do fall on the ground, the plant may take off if there is decent growing weather. Then you have to work harder to keep it under control with growth regulators and protect your crop vigorously as the season progresses to retain what fruit you have on the upper portion of the plant.”

Dodds notes that it’s also important to stay on top of irrigation to maintain the yield potential.

Flowering Phase At Risk

If high temperatures persist as the crop gets into the flowering phase, fertilization and seed numbers will be affected, according to Dr. Derrick Oosterhuis, a Distinguished Professor of Crop Physiology with the University of Arkansas Division of Agriculture.

This is a serious issue because flowering is when the yield is set for the entire season. In addition, a decrease in seed numbers means smaller bolls.

Like Dodds, Oosterhuis urges farmers not to fall behind with their irrigation. He also points out that some research shows boron applications may provide some alleviation of the stress effect on the flower because boron helps with translocation of sugars to the square, flower and boll.

“If you are a producer using boron as a standard practice, my advice is don’t stop,” Oosterhuis says. “It may be of some help.”

As far as making any changes in end-of-season decisions right now, the Arkansas physiologist suggests waiting to see what August weather brings.

“If we have normal August heat, compensation comes in terms of increased boll weight,” Oosterhuis says. “The plant will be able to put more into the seeds and the fiber, even though there may be fewer seeds present, which means yields won’t be down as much.”

It’s true that June and July were tough on Mid-South cotton. But, if farmers catch a late-season temperature break and stay on top of the crop’s needs, a successful finish is not out of the question.

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