MISSISSIPPI STATE -- The cruel irony of the beautiful fall-like weather Mississippians have enjoyed in August is that it's hurting the state's cotton crop.

Cotton needs warm weather, measured as at least 2,150 accumulated heat units, to mature. Tom Barber, Mississippi State University Extension Service cotton specialist, said cotton typically accumulates 20 heat units a day in August. By mid-August this year at Stoneville, cotton had not accumulated 20 heat units in any one day, with most days coming in at six to 11 units.

"The colder weather is slowing the plant down physiologically," Barber said. "It's taking longer for the upper crop to mature and fill out. People who thought they were about two weeks from defoliation the second week in August now find themselves still a long way from it."

Barber said cotton usually progresses from bloom to mature boll in about 40 days. This year, he expects it to take 50 or more days. Compounding the problem is dry weather since early July that followed on the heels of extremely wet weather in June. The excess moisture caused much of the cotton to develop shallow root systems.

"When dry weather arrived, roots couldn't reach the moisture and nutrients, and it caused stress and boll shed in some plants," Barber said.

According to the U.S. Department of Agriculture's Aug. 15 crop report, just 7 percent of the state's cotton has open bolls. The five-year average for this time is 21 percent. They estimated a harvest of 800 pounds of cotton per acre from 1.08 million acres. Average yield is about 750 pounds per acre.

Ann Ruscoe, Coahoma County Extension director, said slow heat unit accumulation is not helping her county's cotton.

"Cotton was slightly ahead of last year and the 30-year average as of the end of July," Ruscoe said. "Since temperatures have fallen off, it may give us some delay and affect the amount of late bolls that we'll be able to mature."

Ruscoe said yields could be considerably less than the 965 pounds an acre harvested in Coahoma County last year.

Charlie Stokes, Extension area agronomic agent in Monroe County, said 99 percent of the cotton in his six-county area is not irrigated. Drought conditions in late July and early August so damaged the cotton's already poor root system that plants were unable to take in nitrogen and other nutrients applied earlier in the season.

"That helped set the stage for the sub-par crop that we've got right now," Stokes said. "We're already behind the 8-ball because of the lack of nitrogen. These cold mornings and evenings have really slowed down the plants' maturity."

Stokes hesitated to estimate a cotton yield in northeast Mississippi, but said "if we pick more than a bale and a third (about 650 pounds) an acre, we're lucky."