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August rains improve cotton outlook

The outlook for cotton in Virginia and North Carolina took a little upswing in late August thanks to rains that fell over much of the growing area.

“It didn't end the drought, but it sure helped,” says Joel Faircloth, Virginia Tech Extension cotton specialist. “This will not be an above-average year for cotton, but we were fortunate to get some rain in most areas towards the end of August that will help fill out a lot of cotton bolls. Mid- to late-August is a critical time to have moisture in cotton.”

Yield in Virginia will probably be below average due to the drought. “That being said, cotton has certainly fared better here than determinant crops like corn,” says Faircloth. “It is remarkable how tolerant cotton is of drought.”

Although it won't be a bumper crop, Faircloth thinks the yield won't fall too far below the average of recent years. “A few weeks ago, I would have estimated we would average 650 pounds per acre. This rain might push it closer to 700.”

Much of the crop was opening very early, and some cotton growers were already defoliating in late-August, about two weeks early, he says. “By the end of the first week in September, we may have 20 to 25 percent defoliated. That is very early for Virginia.”

This is probably a reflection of the drought Virginia has had, says Faircloth. “There are a lot of fields where yields are not good.”

In North Carolina, there had been little regrowth through the third week of August despite some rain.

Significant regrowth is usually expected in a dry year because the plant will eventually find residual nitrogen and have little boll load to invest it in if moisture returns, says Keith Edmisten, North Carolina State University Extension cotton specialist.

“Cotton root development stops during bloom as the plant turns its attention to boll fill,” says Edmisten. “In a drought, the root systems actually die back some. Once the rains return, it often takes a little time, but roots will start to grow again and will find unused nitrogen.”

It is easier to prevent regrowth than to take it off, he says. “In general, I would depend more on Dropp (thidiazuron) than on herbicidal defoliants in order to get enough thidiazuron in the plant to help deal with regrowth. This means the standard high rate of 0.2 pounds of Dropp 50 WP that many of us are familiar with, as the higher rate will maximize regrowth activity.”

If you use a product with a mixture of thidiazuron and diuron, such as Ginstar at a rate high enough to get 0.1 pounds active ingredient of thidiazuron, you will very likely stick leaves, says Edmisten. A better strategy is probably to apply the rate of Ginstar appropriate for the temperature and spike it with enough additional thidiazuron to bring the total in the mixture up to 0.1 pounds active ingredient.

Since the crop was past the last effective bloom date, there was no guarantee that further precipitation would be a positive thing since it might add new growth and fruit, says Jack Bacheler, North Carolina State Extension entomologist. “But better moisture conditions would certainly help fill out existing bolls.”

Late in August, it was announced that Palmer amaranth had spread in Virginia since its discovery in the state the year before.

It was found in the Southampton County, City of Suffolk, Isle of Wight County and Franklin County, says Faircloth. The populations usually appear in soybean and cotton fields, but it is also showing up in neighborhoods and common areas where it was brought in by topsoil.

These populations have generally been fairly isolated and not very dense. Currently, the populations tested in Virginia have displayed resistance to such ALS-inhibiting herbicides as Staple and Envoke, and they are also likely to be resistant to other and perhaps all ALS-inhibiting herbicides.

At this point, there is no reason to suspect the Palmer amaranth in Virginia is glyphosate resistant, but glyphosate-resistant populations have been found in North Carolina within 20 miles of the Virginia state line.

The potential number of seeds produced by one Palmer amaranth plant is tremendous — up to 500,000 seeds per plant, so anything less than 95 percent control is unacceptable, Faircloth says. The growth rate of this weed and the potential for yield loss in row crops in infested fields are exceptional. Once resistance is established, the costs associated with controlling this weed are so high, they can be prohibitive for cotton production.

The good news in Virginia is that with a few exceptions, the areas where this weed has been observed are mostly isolated, and populations are manageable, says Faircloth.

“While realistically we cannot hope to eliminate the spread of this pest in Virginia, we have the opportunity to slow its spread,” says Faircloth. “Inspecting fields now, when Palmer amaranth is most recognizable due to its distinct seed head, is critical.”

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