The sky isn’t falling with the Cotton Leafroll Dwarf Virus, CLRDV with efforts underway across the Cotton Belt to take on the disease.
That’s the message Steve Brown, Auburn University Extension cotton agronomist, delivered to the virtual annual meeting of Southern Cotton Growers and Southeastern Cotton Ginners Jan. 14. Brown emphasized there were a very small number of field disasters from CLRDV across the Cotton Belt in 2019 and 2020. In fact, Brown said the incidence of CLRDV was less in 2020 than it was in 2019.
CLRDV was first reported in Alabama in 2017. It is closely related to a cotton virus known to occur in South America. Historically, that virus has caused up to 80% yield losses in Brazilian cotton fields.
Concerns became heightened when field disasters were reported in southwestern Alabama in 2018. Since then, significant research work across the Cotton Belt has been implemented to get a handle on CLRDV. Brown said land grant universities, USDA and Cotton Incorporated are all involved in tackling the virus. The National Cotton Council has formed a CLRDV working group that has representatives from across the Cotton Belt.
“Clearly this virus can be found throughout the Belt, Texas to Virginia, Oklahoma to Florida. Its prevalence seems to be more common as we go to the lower portion of the Belt. If we look at Alabama, we have much more incidence in lower Alabama than we do in north Alabama,” Brown said.
“The virus we are seeing across the U.S. Cotton Belt is from a single introduction. It can be found from Virginia to Texas. It is essentially the same virus. It is different from the virus that is seen in South America that has been traditionally called blue disease,” Brown said.
CLRDV is an insect vectored virus where aphids carry the pathogens and inject it in cotton as they feed on the plant. Brown said the plants show a wide range of symptoms such as leaf puckering and brittle leaves, but there is still uncertainty if these symptoms are actually caused by CLRDV. He said it is a difficult disease to diagnose in the field.
For the most part, yield does not seem to be significantly hampered by CLRDV. In 2018, significant yield losses were seen in some CLRDV-affected cotton fields in south Alabama. Those fields were planted late in June and likely had high levels of CLRDV infection due to high aphid populations.
Brown said the long-term goal for addressing the virus is the breeding of resistant lines. Breeding research is now underway across the Cotton Belt. The University of Georgia, Auburn University and Mississippi State University are all actively screening lines, looking for lines that offer resistance and immunity.
Both cool season and warm season weeds are seen as hosts for the virus. Brown said both the University of Georgia and Auburn University have a number of research projects examining how weed management and cover crops can limit CLRDV.
Brown said early planting is seen as one effective way to deal with the virus.