By Clint Thompson
A mild winter has Georgia cotton growers wary of potential whitefly problems this year. For producers, the 2020 winter feels eerily similar to 2017 when mild temperatures led to an unprecedented whitefly outbreak that impacted cotton and susceptible vegetable crops.
University of Georgia Cooperative Extension cotton entomologist Phillip Roberts said UGA is encouraging farmers to do anything they can to minimize risk of whiteflies, whether that’s placement of crops, variety selection or planting date.
“We’re still very early and it is true that we’ve had a mild winter, so our risk is elevated when we think about whiteflies. I think we’ll learn much more as we go through March and April. It’s going to be very weather dependent,” Roberts said. “(If) we go through dry conditions and carry those dry conditions into the summer, we’d expect populations to build.”
If whiteflies are left uncontrolled, they can reduce cotton yields and affect the quality of the crop. Whiteflies are sucking insects that feed similarly to aphids. When they feed on a plant, they excrete a sugary substance called “honeydew,” which serves as a host for the sooty mold fungus. The accumulation of honeydew and sooty mold leads to quality problems on open cotton bolls.
Though the presence of whiteflies is likely this year, growers can minimize risk, namely with planting date. Roberts said farmers plant cotton from the middle of April to the end of June, though, nearly 35% to 40% is planted prior to May 10. Some years producers may plant 25% or more in June.
The risk for whitefly pressure is considerably lower in April-planted cotton when compared to cotton planted in mid-to-late June.
“The reason the risk is elevated on late-planted cotton is whiteflies continually build in the summer months and it’s just exponential growth. What we’re looking to do is have that crop mature, defoliated and picked prior to these populations reaching very high levels,” Roberts said. “A whitefly can complete a generation in 15 days, so if your crop is (planted) a month later, that’s two generations. That can be a lot of difference in the size of the pest pressure you deal with.”
Other ways farmers can minimize risk is to plant in fields not in close proximity to whitefly-infested crops and rely on beneficial insects.
“Anything you can do to minimize risk in anything is going to be beneficial in the long run,” Roberts said. “If you know you have certain farms that tend to have more whiteflies, lets plant them first and wait on those where we don’t have as heavy a pressure and plant them last.”