What is in this article?:
- Rain-hindered research confirms thrips could be cotton's No. 1 insect foe
- Insecticide treatment delayed
- Cotton thrips control estimated at $24.50 per acre – $15 to $18 for the seed treatment and $8 for the foliar spray.
- Cotton plant biomass is enhanced by the use of insecticides to control thrips.
THRIPS FEEDING DAMAGE to seedling cotton causes leaf curling, stunted growth and a reduced plant stand.
Insecticide treatment delayed
A cover was in place, he says, when it came time for tilling and planting. “We planted early, on May 3. Typically, when we plant early in the planting window, it’s a good period for thrips to be out there, temperatures are a bit cooler, and cotton doesn’t always grow very well. Generally, we put out our insecticide at the first true leaf, but we were delayed so by the moisture this past year. Also, we put it out the insecticides just before a rain, which isn’t a good idea.”
Reisig looked at thrips abundance and injury ratings, along with plant height and number of leaves, starting at three, four and five weeks after planting. Then, six weeks after planting, he weighed the dry weight above and below the ground. He pulled up the plants when the soil was moist, cutting the plant at the soil line, and took yield from the two middle rows.
“North Carolina really doesn’t have a sophisticated method of irrigating cotton, with less than 2 percent of the acres being irrigated. We used the University of Georgia checkbook method, which is based on crop growth stage. We had a deficit moisture situation on the third week of July, when we put out 1 ½ inch of irrigation. It looked like a deficit moisture situation during the first week of August, but I put out ½ inch which was followed by 3 inches of rain. So it wasn’t the best year to do an irrigation study.”
Conventional untreated plots had some thrips injury, he says. “It looked as though we had smaller plants and a little more injury where we had strip-till, which is contrary what we’ve seen. As we start to increase the cover on the ground, we tend to decrease thrips populations. But also, as we start to move towards reduced-tillage situations, the plants tend to grow a little slower.
Once we got into the reproductive stages and past the thrips-susceptible time, it literally was a wash. We received so much rain, and the field was poorly drained, giving us poor cotton as a result.”
A curious interaction was observed with the irrigation factor, he says.
“Four weeks after planting, we had not put on an irrigation, so it was curious why there would be a significant interaction for irrigation. We used drip tape, and it was apparent in the field, so maybe it was a mulch effect that repelled thrips.
“We had lower insect density where we treated with insecticides and had no irrigation, but we didn’t see the same thing where we did have irrigation and treated, so something’s going on with the drip tape. In general, we had fewer thrips where we treated with insecticides.”
Taller plants were observed where the plots were tilled and treated with insecticides, he says.
“Where we looked at below-ground biomass, we saw a doubling of the amount of biomass where we treated with insecticides compared where we didn’t treat. Whatever goes on above ground is also seen below ground, as has been shown in earlier research from the University of Georgia.”
Tillage type didn’t significantly influence thrips density in 2013, says Reisig. “We had plants that were taller where we used conventional tillage, and below-ground biomass was significantly influenced by the insecticide regime. These results are very preliminary, and it was a very bad year to conduct an irrigation study.”