Cotton farmers across the Southeast and Mid-South are urged to be on the lookout for a new disease, cotton leaf roll dwarf virus, that has scientists worried and wondering just how big a problem it may be now and in the future.
The new virus has been top of mind for many in the Georgia and Alabama cotton industry since it raised its head in August to October of 2017 when plants displaying symptoms of a possible virus were observed in producer fields in several Alabama counties.
Subsequently, the virus was identified as cotton leaf roll dwarf virus (CLRDV) in samples collected from Barbour County in Alabama. In September 2018, cotton plants with similar symptoms were collected from the Alabama Agricultural Experiment Station Plant Breeding Unit in Elmore County. Auburn scientists detected the virus in 24 counties in 2018, while the University of Georgia Extension notes that the virus was detected in 14 Georgia counties.
In late June of this year, CLRDV was also confirmed in Florida, Georgia and Tennessee as well as Mississippi and Louisiana. University of Georgia Extension notes that the virus was detected in 14 Georgia counties in fall 2018.
Symptoms are difficult to diagnose and there are still many unknowns on the damage the disease brings to cotton plants and yield. The job at hand now is to gather information, determine the severity of the disease and seek solutions.
The University of Georgia notes that symptoms include curling, reddening and dropping of leaves, subsequent distortion of leaf growth above the nodes where reddened leaves were first observed and shortening of upper internodes and their discoloration to deep green.
Due to worries about CLRDV, the Southern Cotton Growers Association convened a meeting July 17 of cotton farmers and researchers from across the Southeast as part of its mid-year board meeting at the Ritz Carlton in Amelia Island, Fla. to address the disease. The purpose of the meeting, according to David Ruppenicker, CEO of the association, was to bring stakeholders together to gather information and find solutions moving forward.
“We know a proactive rather than reactive approach is needed in order to get a handle on this,” Ruppenicker said.
“This meeting brought in the top experts who are working on cotton leaf roll dwarf virus. It’s great to see how all of the land grant universities — the University of Georgia, Auburn, North Carolina State University, Clemson, the University of Florida and Virginia Tech — are collaborating in unison for the common good of everybody,” he added. In addition, Mississippi State University is cooperating.
State support funds from Cotton Incorporated are expected to be earmarked for further research on CLRDV. “If this disease grows to become the monster some people are fearing, we will need to seek federal funds to ramp up research and find a cure as quickly as possible,” Ruppenicker said.
The consensus of those who attended the meeting, Ruppenicker said, was that CLRDV presents a serious issue that needs to be addressed. “We are all praying it won’t be as bad a problem as it now appears to be. We need the 2019 growing season for all the land-grant universities to collaborate along with Cotton Incorporated before we spend a lot of money on this problem,” he said.
Jimmy Sanford, a Prattville, Ala., cotton producer and chairman of the Alabama Cotton Commission, chaired the Amelia Island meeting. He emphasized that when it comes to CLRDV, “an ounce of prevention is worth a pound of cure” and the issue needs to be addressed collaboratively to find solutions.
Dr. Austin Hagan, former Extension specialist and professor emeritus of entomology and plant pathology at Auburn University, has been working extensively on CLRDV. He spoke at the Amelia Island meeting, emphasizing that the disease is very difficult to diagnose.
“We are learning as we go, particularly on what the symptoms are and being able to visually diagnose the disease,” Hagan said.
“One particular symptom is plants take on a reddish or maroon cast and some of the plants wilt and die. We are trying to associate the infection with the symptoms and, hopefully, parse those differences and symptom patterns. The reddening and wilting may be associated only with certain lines or varieties. We just don’t know,” he said.
In 2018, symptoms were first observed in early to mid-September at multiple locations across Alabama. Symptoms were particularly severe in June-planted cotton as compared with May-planted cotton.
Hagan emphasizes that early planting may be a cultural practice in managing the disease.
The job now is to gather information, determine the distribution of the disease and monitor yield loss. As of now, Hagan says no yield loss data is available. However, severe loss was observed in a few farmer fields in Alabama in 2018.
One current project led by Hagan in addressing the range of symptoms is the use of sentinel plots. A virus can display a different symptom based on variety or by its environment or the interaction of both. Therefore, sentinel plots for CLRDV are in 15 locations across 10 states: Alabama, Georgia, Florida, South Carolina, North Carolina, Virginia, Louisiana, Mississippi, Arkansas and Texas.
There are five sentinel plots in Alabama with six varieties in all locations being tested for CLRDV.
The disease is transmitted by aphids, but Dr. Phillip Roberts, University of Georgia Extension entomologist, emphasizes that spraying for aphids is not the solution. “We still have a lot to learn about managing the disease. One thing we have proven is we cannot eliminate aphids from the field,” he said.
Roberts points to research done in Brazil that shows winged aphids can transmit the virus in 40 seconds. “There is no way we can stop an aphid from landing and feeding in 40 seconds. Where we sprayed very aggressively every week we had aphids coming back into those plots before we sprayed again. There is no way we can stop the primary spread of aphids, but we can significantly reduce their populations which could minimize secondary spread. What we have to understand is how or even if aphid management influences disease incidence and severity,” he said.
Long-term, establishment of resistant cultivars is viewed as the best defense against CLRDV. Dr. Jenny Koebernick, Auburn’s cotton breeder, says the limited number of commercial cultivars exposed to the virus in 2018 showed symptoms, implying they may not be resistant.
“Resistant varieties will be the backbone of managing this virus. Going forward to develop this resistance, a breeder must identify a line or genotype that will not become infected with the virus when an infected aphid feeds on it,” Koebernick explains.
“Therefore, a lot of work must be done in order to test a whole slew of varieties — commercial cultivars as well as exotic and obsolete material. The commercial companies don’t know if they have resistance because this is the first season it will be looked at. All of the varieties we tested in 2018 came back positive for CLRDV,” Koebernick added. “We will be gathering a lot of information this season as there are so many unknowns.”
Like others, Koebernick says the Amelia Island meeting was important to bring stakeholders together and raise awareness that there is a problem which needs to be addressed. She says the good news is the industry is committed to finding a solution.
“We need to gather as much information as possible to minimize the risk for the growers,” she said.
In the meantime, Dr. Bob Nichols, a senior research director at Cotton Incorporated, emphasizes using fungicides to control CLRDV is not the answer.
“CLRDV is a virus. Using a fungicide to treat CLRDV would be like taking a shot of penicillin for the common cold. Applying fungicides is an inappropriate response,” Nichols said.
Nichols believes CLRDV is an issue that must be addressed. He says Cotton Incorporated is working with the public researchers and industry to find a solution. Like others, he hopes CLRDV won’t become a major issue, but the cotton industry needs to be prepared.
Nichols notes he has personally seen cotton plants with disease symptoms in Alabama, Florida, Georgia and Tennessee. Reports indicate it is also prevalent in Mississippi.
“I have never dealt with a disease where the symptoms are as variable as they are with CLRDV,” Nichols said. “At this point, we have a lot to learn. We need to get through this season and determine the impact. We will need a general post mortem and a consensus report of what we know, what we don’t know and what we need to do going forward.”