Fruiting issues that occurred last year from shedding of four bract squares in some Mississippi cotton were likely caused by high temperatures rather than insects, says Darrin Dodds, assistant Extension professor of plant and soil sciences at Mississippi State University.

“When we started getting reports of squares on the ground, our first thought was plant bugs,” he said at the annual meeting of the Mississippi Agricultural Consultants Association. “But when we looked more closely, we found the shed squares were mostly four bract squares. Research regarding four bract squares points to high temperatures as the cause, rather than insects.

“If we look back to weather conditions last season, about 60 percent of our cotton was planted when temperatures went from cold to very hot and very dry 9 or 10 days later — and it stayed that way the rest of the summer.

“We started seeing blooms about the first week of July; 40 days prior to that, plants would have been in the stage when squares would in the terminal, and temperatures were 6 degrees to 8 degrees above normal. On average, temperatures were 80 degrees or more daytime, and didn’t cool down that much at night. The number of four bract squares shot up dramatically.”

When squares are differentiating in the terminal, Dodds says, high temperatures can cause the plant to attempt to form an additional leaf, which becomes a fourth bract, generally on lower-most branches. These four bract squares are highly susceptible to shedding.

Growers may think the square loss is due to insects, even when low insect populations were present, he says, but “while four bract squares can be an entry point for multiple insects, more often than not the squares will end up on the ground as a result of having four bracts, and there will be some yield loss as a result.”

In such situations, he says, the crop will need to be managed “a little more aggressively” with plant growth regulators.

“When fruit retention starts to decline, plants want to take off and run, so a PGR should be used to keep height under control. Also, insects need to managed more intensively.

“If you’ve already lost some of your fruiting potential because of four-bract squares, you don’t want to lose additional squares to insects. And you will want to manage other stress factors, particularly irrigation. If you’ve lost some squares and have fruit retention issues, the last thing you want to do is stress cotton by waiting until it has been blooming a week or 10 days before starting irrigation.

“If you have a four bract square situation, you need to be proactive with management in order to reduce the impact.”

Addressing other cotton topics, Dodds says variety selection is becoming “a more complicated decision” for growers.

“There are a lot of choices now, compared to the period from the early 1960s into the early 1980s, when there were only about two to four varieties planted on the majority of the  acres in Mississippi.

“Contrast that to 2000, when over 50 varieties were planted in the state — including some conventional varieties, some BXN47, first generation Roundup Ready varieties — a lot of different choices. As we moved on, the conventionals and BXNs all but went away, but in 2010 we still had 36 or 37 varieties.