Thrips control in cotton will continue to grow in importance as producers push for peak performance from new high-yielding varieties, says Ron Smith, Auburn University Extension entomologist.
“Thrips control will be more important in the future than in the past because the new high-yielding varieties will achieve those yields only if we remove limiting factors like thrips damage,” said Smith at the Cotton Pickin’ Roundtable held in Shorter, Ala. “If you’re growing 750-pound cotton, thrips control isn’t nearly as important as if you’re growing 4 to 4 ½ bales per acre. Our varieties today have that potential under perfect weather conditions, and growers have already proven it.”
He conducted six thrips trials in Alabama last year, with four of them in the central part of the state. “One of the best ways to evaluate is by eyesight. The number of thrips doesn’t matter so much as how it makes the cotton look. We have a scale that is being used from here to Virginia. After 45 days, we take a sample of the seedling at the soil line, dry it down, and then weigh the biomass. That correlates very well with thrips control – how big are the plants and how much do they weigh after 45 days and they are dried down.”
Yields are not always a good indication, he adds. “A lot can happen between seedling cotton and harvest time, including weather factors and other things. We use a 1 to 5 scale, with 1 being no thrips injury and 5 meaning that the thrips are killing the plants.
“If you plant from the beginning of planting season up until around May 10, the seed treatments will give you about a No. 3 on our damage scale. That’s the breaking point where, if we’re scoring it, we’d recommend making a foliar spray. From April 10 to about May 10, the seed treatments will give you control that would still require a foliar spray. If you plant later in the season and the nights are warmer and the cotton is growing faster, the same level of thrips would do less damage and you’d get by without that foliar spray,” says Smith.
If you decide you’re going to put a pound of acetate or Othene in-furrow, and you leave off the seed treatment, you’re normally score about a 4 on the damage scale – a little bit better than nothing, he says.
Thrips hit every cotton acre every year
From his six trials in 2013, Smith reached a few conclusions.
“There’s no doubt that thrips are the most widespread insect pest of cotton because they affect every acre every year across the entire Cotton Belt,” he says. “They’ll likely always be a factor in cotton production. I don’t see any technology or anything coming in the future that’ll keep thrips from always being a factor.”
It’s also important to remember that thrips damage in an individual field is influenced by several things, says Smith. “These include planting date and weather. Weather could have an impact on the thrips themselves, on cotton, or, like last year, on the wild hosts where thrips are coming from. Rainfall amounts and nighttime temperatures impact thrips the most.”
Another factor, he says, is the tillage system being used. “You get fewer thrips in a reduced tillage system. The more litter that’s on the ground, the fewer thrips you’ll have. We don’t exactly understand that, but thrips are much heavier in conventional tillage systems.”
Additional factors affecting thrips pressure include the in-furrow seed treatments used at planting and whether or not you make a foliar spray on top of the in-furrow seed treatment.