Extension professionals have already confirmed the presence of cotton leafroll dwarf virus (CLRDV)—the causal agent of cotton blue disease — on multiple research substations across Alabama. The aphid-transmitted disease has been monitored closely since it appeared in cotton fields during fall 2017.
Kassie Conner, an Alabama Extension plant pathologist, said the virus was confirmed in samples taken since July 1. The first diagnostic test was not available for the virus until October 2018, which made it difficult to identify plants with symptoms during the 2018 growing season.
“This does not mean the virus was not present earlier, it only means we did not have the capability to test for the virus until then,” Conner said. “Last summer, symptomatic plants were found at substations as early as mid-September, with the worst damage recorded in June-planted cotton in fields in Baldwin County.”
Conner, who is also the director of the Auburn University plant diagnostic lab, said specialists have also identified several weed species that are alternate hosts for CLRDV. The most alarming hosts are white clover and henbit — common weeds found all over Alabama. This confirms a heavy virus presence in the environment.
Symptoms from early season infections include:
► Compacted terminal growth.
► Upward-cupped leaves.
► Red discoloration of petioles and stems.
► Distorted growth with yellowing around leaf edges.
► Crinkled leaves.
Submitting Plant Samples
Conner and other Extension and university researchers are requesting sample submissions. A submission form with sampling directions should accompany each submission.
Conner said the data will help researchers better understand the development and distribution of the disease.
Follow these steps when collecting samples:
► Collect five samples from symptomatic plants and non-symptomatic plants at each location (one sample = top 6 inches of plant).
► Place samples in a sealable plastic bag with no other material (no paper towels).
► Keep sample cool—place in a cooler, refrigerate until shipped and ship overnight with an icepack in a styrofoam cooler.
► If aphids are present, collect and send them on the plant material.
► Include a submission form and shipping permit in a separate sealed bag in the package. Shipping permits are only necessary if samples originate outside of Alabama.
► Email Conner before mailing samples to obtain a shipping permit if necessary. Include photos of symptomatic plants in the email.
Varietal Resistance Options For Producers
Jenny Koebernick, the Auburn University cotton breeder, is currently screening nearly 1500 cotton varieties in Tallassee and Fairhope looking for resistance to the virus.“At this time there is not a variety or cultivar identified with resistance to the strain of CLRDV that we have in Alabama, but this is because nothing has ever been tested,” Koebernick said. “This is one of the reasons that plant samples are so important to our research.”
Alana Jacobson, an Auburn University research entomologist, said right now there is limited information about factors surrounding disease development and spread.
“Every tissue sample submission will help us collect information about the virus,” Jacobson said. “There will be many factors that influence disease onset and spread. Variety and environmental conditions will play a role in disease severity.”
The collection and analysis of samples to determine varietal sensitivity and susceptibility are essential to targeted research.
“Even management practices will be valuable pieces of the puzzle as they work to set research goals and priorities,” Koebernick said. “Our main goal is to learn everything we can about the disease in order to help farmers minimize risks.”
Find more information about Cotton Leaf Roll Dwarf Virus in Alabama Extension’s ANR-2539.
The Alabama Cooperative Extension Service contributed this article.