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September watering rarely pays for cotton

Weather will play a role in whether watering late cotton will have a payout.

If Hurricane Ida misses your cotton field – and most farmers probably have mixed feelings about whether they would welcome both the rain and winds – don’t worry about having to make up for the missed moisture.

That’s the advice of Dr. Bill Robertson, Extension agronomist – cotton with the University of Arkansas System Division of Agriculture, who was interviewed before Ida began taking aim at the Gulf Coast of Louisiana on Aug. 26.

This year’s Mid-South cotton crop is generally considered to be two to three weeks late, primarily due to weather problems at planting and the unusual rainfall events that followed. Because of that, growers may be tempted to turn their irrigation pumps on one more time – if Ida doesn’t dump several inches of rain on their fields.

“Watering cotton in September rarely pays,” said Robertson, who says he’s been receiving calls from farmers asking if they should continue to irrigate beyond the normal calendar cutoff date.

“You have a center pivot or the polypipe is already laid, and all you have to do is flip a switch and water it one more time to try to give you a little peace of mind that you did everything you could to set those later bolls,” he said. “That’s a perfectly reasonable mindset.

“I don’t have any data on this, but, when we look at it to see how it does compared to some of the other fields, that one last watering doesn’t make us any additional cotton. What it does do is cost us some days getting the picker in the field because it gives the cotton plant a second wind.”

Robertson compared cotton to putting a grandchild down for a nap an hour or two before bedtime. When it gets a second wind, the cotton isn’t ready for a nap or for a harvest aid application.

“A lot of time that extra irrigation doesn’t give us extra yield, and it costs us days for getting the picker in the field,” he noted. “We need to look at our crop and try not to be tempted to put that extra water on.”

Cut out

Having five nodes above white flower or NAWF-5 is generally considered cut out for Arkansas’ cotton acres that are grown on silt loam soils. The soils tend to seal over during a rain and limit the amount of water than infiltrate those soils.

“On the day of cutout those first position white flowers out there represent bolls that are going to contribute to yields and profit,” he said. “We will have other bolls come on after that, but it takes way more white flowers to end up as bolls to make a pound of cotton after that. Those bolls will be smaller and have less quality.

“When we reach nodes above white flower 5 I think of the white flowers that are there as being our last money bolls.”

Entomologist recommend terminating insecticide applications based on the number of heat units accumulated after cutout – 250 heat units for plant bugs, 350 heat units for worms, 450 for stink bugs and 500 for defoliators.

“Irrigation isn’t as straightforward,” he said. “I’ve seen fields where we have good infiltration down to two and three feet and a good root system. In a field like that we can terminate irrigation at 350 to 450 heat units after cutout and not hurt yield.

“But with our poor infiltration and shallow roots a lot of times we end up terminating irrigation between 500 and 550 heat units past cutout. I have watered cotton at 600 heat units, but I don’t think it really helped on yield.”

For most of Arkansas’ cotton irrigation is normally terminated at 500 to 550 heat units, he said. “But on some of our late-planted field this year, this will put us into September. We need to look at the weather and other factors, but pushing it at the end of a season like this can often do more harm than good.”

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