Alabama Cooperative Extension System scientists have confirmed the presence of cotton leafroll dwarf virus in Alabama cotton. This confirmation comes one month earlier than it did in 2019 and that concerns them.
“Typically, the earlier disease onset occurs, the greater the associated yield loss,” said Austin Hagan, an Alabama Extension plant pathologist. “We found CLRDV-AL in sentinel plots during the week of June 8.”
Hagan is part of a team of Alabama Extension and Auburn University scientists tracking the potentially devastating disease.
Early warning system
“Sentinel plots act as an early warning system,” he said. “We will put more plots in across the state as planting season progresses and will actively monitor them.”
The first cotton seedling samples taken from these plots showed leaf puckering or blistering. Hagan said this is a symptom associated with cotton leafroll dwarf disease, also known as cotton blue disease. While a visual diagnosis can be complicated by thrips damage, lab testing confirmed CLRDV in about 30% of the samples collected.
“All of the cotton varieties in the sentinel plots tested positive,” he said.
First observed in 2017 in the state, the disease, which is spread by aphids, was widely detected across Alabama in 2019. The virus appears to be present at some level in most Alabama cotton fields.
Challenge to control
“Farmers don’t have effective control options for the disease,” Hagan said. “Multiple insecticide applications to control aphids will not suppress disease spread.”
Alabama Extension cotton agronomist Steve Brown said aphids are difficult to control even with intense management.
“In research plots, entomologists can never completely eliminate aphids, even with aggressive insecticide applications,” Brown said. “We know we cannot manage the disease by efforts to control aphids.”
Kassie Conner, also an Alabama Extension plant pathologist, said alternate plant hosts for the disease may explain the earlier appearance.
“The virus appears to be building in alternate hosts such as some common weeds,” Conner said. “We might have started the season with a higher virus load and that led to earlier infection in cotton and earlier disease onset.”
They know henbit, white clover, Carolina geranium, evening primrose as well as chickweed act as hosts for the virus, she said. However, there may be many more weeds that they have yet to identify as potential hosts.
Crop practices that reduce impact
Brown said some crop management practices may help reduce the disease’s impact.
Plant early. Researchers have observed reduced virus effects in early cotton. Also, late plantings tend to have increased risk for significant yield effects.
Stalk destruction. Cutting stalks off at the ground eliminates some overwintering habitats for aphids and the virus. This also prevents stalk regrowth where aphids could acquire the virus.
Winter weed control. Control and remove winter weeds.
Cover crops. Research evaluations continue to determine the best cover crop options.
The Alabama Cooperative Extension System contributed this article.