June 2, 2023
Each crop year brings a new set of pressures and concerns, and that is no different in 2023. While Louisiana and Mississippi have found redbanded stinkbugs, that is not necessarily the case for Arkansas. Ben Thrash, Extension entomologist at the University of Arkansas System Division of Agriculture, weighs in on the pesty insects making their way into the field and what farmers can do to control them.
Thrash offers recommendations for black cutworms and armyworms found in both corn and rice. He also lends reminders for thrips control in cotton and recommendations for those who planted ThryvOn cotton this year.
“We got the cutworms, and we got the armyworms, but we did not get the stinkbugs. So far, we have had a decent number of black cutworms primarily in corn and rice this year. Typically, they are not too big of an issue in rice, but we do have a threshold in corn,” he said.
Armyworms and cutworms
Fields having the biggest issues with armyworms and cutworms are primarily those with heavy residue. Thrash said they are finding the cutworms hiding under the old residue that provides plenty of cover for them in the field. While scouting, you may notice evidence of feeding and not see the cutworms. They can be hard to find in the field, and you may have to dig for them.
“Cutworms can be hiding in holes they have dug in the ground, so you may have to dig a hole with your pocketknife to really find them. They can also be under the residue in the field, and you have to dig through that residue. They blend in well, and they are just difficult to see sometimes,” he said.
Thrash noted the threshold for cutworms in corn is about five percent damaged plants.
“Whenever those cutworms cut the corn plant off, they actually delay the maturity of those cut plants a little. If you get too many of those out there in a corn field, it can start to have a little drag on your yield. So, you do not want to get too many cutoff corn plants with those black cutworms,” he said.
Some farmers are getting close to the threshold and have plans to put out an herbicide application within a week. They have asked if they could wait to treat the cutworms with that application. Thrash says, in that situation, it is okay to wait.
“I would not make a special trip out in the field for cutworms or armyworms in the corn. If you do need to treat them, a lot of times you can just throw in a pyrethroid with whatever herbicide you are running across the field.”
Another thing to note is that cutworms may only be along a field edge or in one area of the field. In that case, farmers can consider a strip application to save the cost of treating the whole field.
When it comes to armyworms and cutworms in early rice, Thrash says not to worry. The rice will recover from any defoliation occurring in the field, because the plants will overcompensate for the pest pressure.
“A lot of the work that Nick Bateman has done has shown that when we did get a little defoliation in some of this early, small rice – we actually got a yield bump in a lot of cases. The data he collected is pretty clear, so we are not really concerned about defoliation in a rice field from the cutworms or armyworms.”
Thrips in cotton
Thrips season is upon us. Thrash referred to the Thrips Infestation Predictor for Cotton, by North Carolina State University. He said it predicted the worst population for thrips for Arkansas to be around mid-May. We are just now getting into thrips, and he expects them to increase around that time.
“We will see how good the model is this year, but it is supposed to be on par with last year according to the thrips predictor,” he said.
When it comes to treating thrips, that depends on whether you planted ThryvOn cotton. Thrash said he continues to recommend not treating ThryvOn cotton for thrips.
“I have recommended this for the past couple of years. Do not treat ThryvOn cotton for thrips. That is the consensus among all the Midsouth entomologists. You are still going to have thrips on those ThryvOn plants, and you may have a lot of thrips on those ThryvOn plants, but I am completely confident in not treating the ThryvOn cotton for thrips,” he confirmed.
Research on thresholds for ThryvOn cotton continues. Thrash said they are still working to establish recommendations to ensure that ThryvOn cotton is as profitable as possible for the growers.
When it comes to thrips injury, he also noted that sometimes it can be a little difficult to determine the difference between thrips injury versus herbicide injury.
“We are putting out some pretty stout herbicides to take care of pigweed and other resistant weeds,” he said. “A lot of those herbicides are really harsh and can ding up our cotton plants pretty good. Sometimes it can be a little confusing to tell the difference in herbicide injury, thrips injury, or a combination of both.”
For all other cotton, it is important to remember that we have widespread resistance to the organophosphate insecticides on tobacco thrips. According to data, Thrash said the resistance seems to be getting progressively worse each year. In these instances, a foliar treatment is recommended with Intrepid Edge.
“The only product that is labeled and doing a whole lot of good right now is Intrepid Edge. If you have to go out with a foliar insecticide for control of tobacco thrips on cotton, that is what we recommend,” he said.
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