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Blue disease, which is caused by the aphid transmitted virus cotton leafroll dwarf, was tenatively identified in cotton collected in Barbour and Henry Co in 2017. Cotton with similar symptoms was observed at very low levels at two locations in Southwest Georgia. Presence of this virus has not been detected in the Georgia cotton but was found in the initial but not subsequent Alabama samples. This virus may be unstable and may 'disappear' in host tissues over time. Blue disease is responsible for sizable yield losses in Brazil in susceptible cotton cultivars as well as countires across tropical Africa.
All cotton cultivars marketed in the Southeast are susceptible to blue disease. Symptoms do not appear existing leaves but new leaves are stunted and often cupped or crinkly with a leathery appearance and deep green to almost blue color. The veins on young leaves may also turn yellow. Once infected, plant growth essentially stops as does boll set and maturation. Symptoms can easily be confused with those of phenoxy herbicide injury with the notable exception that individual or several diseased virus-infected plants probably will be found as compared with widespread damaged plants more often associated with overspray or drift events.
At this point, disease incidence in Alabama cotton appears to be very low. Grower or their scouts, particularly those in Southeast AL, need to be on the lookout for symptomatic plants. If you observe diseased plants, contact your Regional Extension Agent, state specialist, or Auburn University Plant Diagnostic Laboratory for further information.
As noted above, all cotton cultivars are susceptible to blue disease. Single gene resistance is available in commercial cotton germplasm but time will be needed if the disease intensifies to deploy resistant cultivars adapated to the Southeast. Control of weed hosts may help slow the spread of blue disease. Malvacaea weeds such as pigweed and prickly sida are hosts of this virus, so control of these weeds in a field and around field borders may slow virus movement into production fields. One observer mentioned that diseased plants were clusted along the field border, so weed control may help with disease avoidence. The value of controlling the aphid vector with post-plant insecticides is questionable as overspraying could lead to outbreaks of other arthropod pests, particularly spider mites.
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