They’re Here. Get Your Game On.
• By Carroll Smith,
Cotton insects come in all shapes and sizes. But one thing they have in common is a voracious appetite for the cotton plant. As we move into the season, it’s hard to predict exactly which insects will show up and how high the populations will be.
However, everyone knows they are out there. A good defense begins with diligent scouting and making sure you have a plan in place to deal with them.
Some of the usual suspects that concern cotton farmers this year are thrips, plant bugs and bollworms, particularly in two-gene cotton.
Thrips And Plant Bugs
In his Pest Patrol Alert report on May 24, Arkansas entomologist Gus Lorenz says thrips don’t seem to be too bad this year.
“These are some of the mildest thrips infestations I’ve seen in a long time,” he says. “However, we have some fields in south Arkansas that are starting to square, and I am interested to see how bad the plant bugs are going to be. Based on our ditch bank surveys, they could be bad, but we will wait and see.
Louisiana cotton consultant Ashley Peters says he starts scouting for plant bugs before the cotton starts putting on small squares. In the early fruiting stage, he definitely looks at hot spots and the places he normally finds plant bugs.
“We use Transform WG insecticide to control plant bugs,” he says. “To rotate chemistries, we may apply an imidacloprid on our first shot and then go to Transform at a rate of an ounce and a half per acre. Sometimes we put out back-to-back shots of Transform, which typically carries us for multiple weeks.”
Auburn University’s Extension entomologist Ron Smith advises growers to not let plant bugs become embedded.
“When this happens, multiple applications will be required to prevent economic damage,” he says. “An embedded situation is when a sub-threshold level has been allowed to go untreated for more than a generation. This results in a plant bug population of all ages and stages from adults, to all ages of immatures and eggs.
“In Alabama, most adult plant bugs move from wild hosts to cotton by July 10, early bloom. Some of the more commonly used choices for an early bloom plant bug spray are Bidrin, Transform, Centric, or bifenthrin to control the adults.”
Bollworms In Two-Gene Cotton
In 2017, bollworms plagued many farmers in fields planted to two-gene cotton.
In regard to the potential bollworm issue Smith says, “This situation may increase this year and in future years on two-gene cotton due to bollworm resistance to both genes. More varieties will be available with three genes in 2018, but supplies of many will be limited. Until the three-gene varieties are widely planted, we need to focus on closer scouting and better management of bollworms in the two-gene varieties.”
The Alabama entomologist recommends monitoring cotton closely for corn earworms coming from corn. He says this historically has occurred about July 10-15 in south Alabama, July 20 in central Alabama and about Aug. 1-5 in north Alabama. The egg lay may last from seven to 10 days in any given location.
“When this flight is detected by increased egg numbers or five to 10 one- to two-day-old larvae in white blooms, have your control plan ready and implement it within 24-48 hours,” Smith says. “We basically have two choices, a pyrethroid at the highest labelled rate, or one of the diamide selections: Prevathon 14-18 oz or Beseige (Karate + Prevathon) at 7-9 oz/ac. The pyrethroid will cost $2.00-$4.00/ac, the diamide class $14-$18/ac. If the bollworm larvae are five or more days old, the diamide may be no more effective than a pyrethroid.
“Diamides are most effective when the residue is on the plant when the egg hatches. In order to make this happen then, we must trigger the spray on or shortly after the historical date for the bollworm moth flight determined by egg or small larvae counts.”
Before the beginning of the 2018 season, Mississippi State University research and Extension entomologist Jeff Gore speculated that it is highly likely that two-gene cotton will have to be sprayed at least once for bollworm this year.
“The three-gene cottons are not immune to bollworm and there may be rare cases where they have to be sprayed as well,” Gore says. “Again, it is going to be critical to know where the two-gene varieties and the three-gene varieties are planted because our thresholds are different. On the two-gene cottons, we suggest spraying based on the presence of eggs.”
Although it is not published in the Insect Control Guide, Gore says these are the thresholds:
• 20 percent eggs anywhere on the plants for the two-gene cottons (Bollgard II, TwinLink and WideStrike)
• 4 percent worms or 6 percent damage for the three-gene cottons (Bollgard 3, TwinLink Plus and WideStrike 3)
“Remember, know where each cotton type is planted to avoid making unnecessary applications on three-gene cotton because somebody wasn’t sure where it was,” he says. “This knowledge can reduce overall costs.”
The insect control take-home message at this point in the season is to continue to scout closely and make timely sprays. Get them before they get your cotton crop.