Cotton loves hot weather — the hotter, the better. Right? We’ve all heard that maxim for years.

Few people know the workings of cotton better than Bill Meredith, USDA geneticist at Stoneville, Miss., and he says very hot weather like we had in July is more foe than friend.

“The major impact of weather on cotton is temperature,” he told members of the Delta Council’s Ginning and Cotton Quality Improvement Committee at their joint meeting with the Southern Cotton Ginners Association. “High temperatures can have a very strong negative effect on yield.

“Temperature accounts for about 20 percent of the variability in yield, and that’s pretty high, when you consider all the other variables that can affect a crop.”

Citing research by USDA Geneticist William Pettigrew on temperature effects on cotton, Meredith says the bottom line is: “The hotter it gets, you lose yield. Bolls are fewer and smaller.”

Even in the record cotton yield year 2004, Pettigrew recorded a loss of 123 pounds of lint per acre because of high temperatures.

Temperature affects length, too, Meredith notes — the hotter the temps, the shorter the fiber. “About 40 percent of the variability in length can be attributed to temperature.”

Micronaire has been steadily increasing for the last 25 years, primarily due to the varieties being grown, he says, and it, too, is affected by temperature. “In general, the hotter the weather, the higher the mike. But if it’s so hot and so dry the cotton burns up and bolls don’t mature, micronaire will be lower.”

Temperature affects strength only slightly and the effect on uniformity is “basically zero.”

Uniformity, primarily a measure of short fiber content, has become a challenge in selling cotton overseas, Meredith says. “We’re going to sell more of it if we can do something to improve uniformity.”

So, given the wide variability in planting dates and weather for this year’s crop, what can growers do for their cotton from now on out?

“Fifty percent of this crop still has plenty of time to develop and produce good cotton,” Meredith says. “But a lot of dryland cotton that hasn’t had a good rain since June is pretty much past the point of no return in terms of useful bolls; I don’t think a rain now will increase yield or quality.”

A lot of growers “waste money irrigating late, thinking they’re going to fill out bolls. I don’t know of any data to support that. There are exceptions, but with the cost of diesel the way it is, I don’t know that you’re going to get any benefit from watering past Aug. 10-15.”

All growers, Meredith says, need to begin getting organized for a quick harvest. “Get everything ready and be prepared to go. I think one reason our yields have been going up in recent years is that we’re getting the crop out of the field and to the gin more quickly, reducing exposure to the weather.”

And he says, “don’t over-manage your crop — don’t be applying miracle products that just cost money, or making expensive late season fertilizer applications.”

e-mail: hbrandon@farmpress.com