Cotton fields in the South are ravaged by thrips each year. While there are seed treatments available to producers for thrips control, many fields still see moderate thrips damage.
Alabama Cooperative Extension researchers are beginning the second year of trials to study the use of cover crop residue as a deterrent for thrips.
Retired Extension Entomologist Ron Smith Ph.D., conducted the first trial, funded by the Alabama Cotton Commission, in 2015 because of a developing level of resistance to seed treatments.
Christy Hicks, an Alabama Extension regional crops agent, is assisting Smith in the second round of trials, set to begin in mid-April.
Resistance to Seed Treatments
Smith said resistance-when it occurs-usually increases.
"The seed treatments currently available to farmers are two different chemistries in the same family," Smith said. "After sending thrips samples to be tested, it was determined that 20 to 40 percent of thrips from different locations were resistant. Of the 20 to 40 percent that are resistant, 20 percent are resistant to only one of the chemistries, 20 percent are resistant to the other chemistry and 60 percent are resistant to both of the chemistries."
Other insects, like aphids, build resistance quickly because of short reproductive cycles, but researchers are unsure about the rate of resistance build up in thrips populations.
Alabama Thrips Control Trials
Alabama Extension researchers are honing in on thrips control and working to determine the level of resistance. Trial results in Georgia identified cover crop residue as a viable option for thrips control and prompted Smith to develop his own trial version in Alabama.
"No one yet knows why residue keeps thrips away, but residue was the only treatment in our trials that held thrips damage below an economic damage level in the 2015 tests," Smith said.
The trial was conducted at the Prattville Agricultural Research Unit, using bales of straw to simulate cover crop residue. Some plots had crop residue, in addition to plots with the seed treatment options available to farmers. One bale of straw per test plot (four rows wide by 30 feet long) was used to simulatea thick winter grain burned down-ground cover so thick the soil wasn't visible.
Each of the trial plots would have required thrips control, except those with residue. If research continues to show profitability in using this technique, residue alone may save farmers eight to $16 per acre and eliminate the need for seed treatments.
Profitability for Producers
Hicks said farmers are interested in the use of cover crops as a thrips deterrent, but the expense may be an obstacle.
Cotton plants with thrips damage and no cover crop residue.
"Producers need to understand what they are getting into before jumping head first into a different thrips control option," she said. "Factor in equipment updates, timely planting and burn down, nitrogen applications and planter set up because these are additional costs of using cover crops for thrips control."
Smith said this form of thrips control is a fairly expensive proposition, and most farmers will not do it for a single benefit.
"Producers already looking for winter erosion prevention and spring weed control will be more likely to plant cover crops for the added bonus of thrips control," he said.
Hicks said while planting into cover does delay plant time, producers reap the benefit of higher soil moisture levels in the summer-another benefit in addition to thrips control.