Thrips are a unique pest for North Carolina cotton farmers because they are a problem in every single field which is why North Carolina State University researchers are looking at new ways to control the insect, according to Dominic Reisig, North Carolina Extension entomologist.
Speaking at the North Carolina Cotton Field Day at the Upper Coastal Plain Research Station in Rocky Mount Sept. 10, Reisig said cool conditions in North Carolina right after cotton planting creates the ideal environment for thrips, which is one of the reason NC State recommends an insecticidal seed treatment plus a foliar spray of Orthene on every acre for control.
This year, NC State is recommending a different thrips control method which features a neonicotinoid insecticidal seed treatment plus a neonicotinoid in-furrow treatment, Reisig said.
"In four true leaf stage cotton, injury from thrips was cut in half using one method of application for Admire Pro in-furrow overtop and insecticidal seed treatment, compared to an insecticidal seed treatment alone,” Reisig explained. “Other methods of application from Admire Pro in-furrow only cut the injury by one quarter. It is important to get contact with the seed at planting for Admire Pro to work the best."
Reisig said application method and the use of seed cover is important for control. An insecticidal seed treatment plus an in-furrow treatment is critical, he said, adding that there is a definite advantage to using an Admire Pro in-furrow.
“We know that thrips will hit the cotton plant as soon as it cracks the ground so you want to get that insecticide that’s taken up systemically as quickly in the plant as possible so that you can protect it. I think you’re going to do that if you focus on getting the insecticide on the seed,” he said.
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Tillage practices are also important for thrips control, said Alan Meijer, North Carolina Extension tillage and soil management specialist. Research shows there is a significant reduction in thrips pressure when growers switch from conventional tillage to strip tillage, he added.
“Thrips inhibit rooting. As tillage decreases, we know that thrips pressure is decreased. As tillage decreases, we know we tend to have better soil moisture storage,” Meijer said. “With the addition of irrigation we’re hoping that if we’re seeing a reduction in either above or below ground biomass due to thrips pressure, the subsequent moisture supplied through irrigation may help that plant overcome that earlier injury.”
Meanwhile, Reisig points out other plant bugs are becoming more of a challenge to North Carolina cotton producers. That is why farmers throughout the state must be vigilant in scouting, he stressed.
“When I started five years ago I was told that plant bugs are not an issue in North Carolina cotton and I think that was correct,” Reisig said. “The places where we did have plant bug problems were in the northeast and they were areas of vegetable production.”
Reisig said plant bugs have now moved beyond the northeastern part of the state further into the Coastal Plain. Late planted cotton is most at risk for plant bugs, Reisig said.
“I don’t see the problem going away. And I don’t know what’s causing it. But they’re here and they’re here to stay. Fortunately we can manage the plant bugs,” he said.
Reisig said the first thing cotton growers need to do to control plant bugs is sample.
“You need to start your sampling early season before the plant flowers. These things will feed on squares, which make the blooms and make the bolls. If you don’t have a square, you’re not going to have a boll. It is incredibly important to monitor square retention early season. You want to keep your square retention above 80 percent,” he said.
Once farmers find that square retention has dropped below 80 percent, they should put a sweep net in the field, Reisig advised. “If you find eight in 100 sweeps, it is time to spray,” he said.
“Early season neonicotinoid class insecticides tend to work well. They preserve beneficial insects and you see fewer problems with flare ups of boll worms, fewer mite problems, and fewer aphid problems, assuming they are not resistant,” Reisig said.
Reisig points out that plants and weed serve as sources of plant bugs while some plants serve as sinks for plant bugs. Some plants serve as both sources and sinks for plant bugs. Vegetables serve as a source of plant bugs while cotton is a sink of plant bugs.
“A sink is something that’s not producing plant bugs, but it can be attracted to plant bugs and a place where they can move and cause problems,” Reisig said.
“Fortunately cotton is just a sink for plant bugs. The disadvantage of a sink is that it’s something that’s attracting plant bugs throughout the season so it’s not like a worm situation where you get a flight in where they lay eggs and develop. For plant bugs you really have to manage them throughout the season,” he added.