Cotton leafroll dwarf virus (CLRDV) is a new disease to North America that has made headlines this past year as Extension workers and scientists rush to understand this cotton virus, which has the potential to create significant yield loss. However, is CLRDV currently a major concern from a yield loss standpoint?
At the 2020 Louisiana Agricultural Technology & Management Conference in early February, Trey Price from the LSU AgCenter said he's not sure.
Price discussed cotton leafroll dwarf virus in the cotton breakout session.
"Is cotton leafroll dwarf virus a threat to Louisiana cotton production?" Price asked. "I could say that it's unclear at this point whether this virus is going to cause yield loss, but so far, it has not shown significant yield losses in Louisiana."
The virus was discovered in Alabama in 2018. Initially, there were conflicting statements concerning yield loss due to the virus.
"It is an aphid-transmitted virus, and it's from South America, but it is a different strain from the one causing significant yield loss," he said. "It's said the virus is transmitted within 40 seconds of the first encounter. Some U.S. entomologists have different opinions on that."
The U.S. strain is atypical compared to the other one and has been associated with many different symptoms.
"There is a wide range of virus symptoms. You name it, and it might be a symptom attributed to this virus, correctly or incorrectly," Price said. "I've seen things happen in cotton over my career that causes cotton to do some of these things that I would not attribute to the virus, so I don't think these symptoms always point to the virus."
A list of symptoms that could indicate issues in cotton other than the virus includes, but is not limited to, insect and mite damage, herbicide damage, physical damage, PGR overdose, or even varietal characteristics.
"Hank Jones, Louisiana crop consultant, and I picked many leaves in numerous fields that didn't quite look right to us, and had them tested for the virus," Price said. "They were all negative according to the lab tests. I guess it was just that particular variety at the time looked different for whatever reason."
Social media is another problem with spreading misinformation on CLRDV.
"I've seen a lot of photos this year on Twitter that have been attributed to the cotton leafroll dwarf virus," Price said. "Some I would say are probably the virus, but some I'm not so sure.
"Some symptoms I can buy into, such as the whips at the top of taller plants in a field, buggy whips as they are described. Particularly if they are clustered in groups. That makes sense in terms of an aphid infestations, which can transmit the virus," he said.
"I'm always skeptical of social media posts regarding CLRDV. They are a snapshot in time and don’t provide the whole story of what has gone on during the season up to that point. What I like to see are pictures that show plants that were sent to a laboratory and confirmed positive or negative rather than speculation.
Keep virus in perspective
"Remember, there may only be a handful of plants in a whole field experiencing virus symptoms while the rest are producing a good crop, so a little perspective is important," Price said.
"Not everyone monitors fields closely all season, plants may be exhibiting some of the CLRDV symptoms at the end of the season, and then they may see something that concerns them that may or may not be the virus. I think the best way to figure this out is to track known infected plants throughout the entire season. Then we can properly define disease symptoms along with other problems and move forward to fix the issue."
In Louisiana during 2019, it was estimated that one in 10,000 plants in a field could have the virus.
"I thought the overall yield impact was minimal this past season, and our yields were good," he said. "It's something we should watch since Brazil has seen yield losses with their strain, but our strain is different. At this point, it isn't at the top of my list of concerns in cotton."