How To Identify And Manage Target Spot And Areolate Mildew
Dadeville, Alabama
The diagnosis and management of foliar diseases in cotton is an area of focus for Cotton Incorporated’s Agricultural and Environmental Research team.
In the Southeastern states of the Cotton Belt, target spot and areolate mildew rise to the top of the list of troublesome cotton foliar diseases. Knowing that these two diseases pose a high risk of negative effects later in cotton’s growing season, Cotton Incorporated has teamed up with the University of Georgia to fund research on how to identify and manage these issues.
Identifying Foliar Disease
Target spot can be easily recognized by the appearance of rings on the leaf, hence the name “target spot.” Characteristic symptoms of target spot include brown lesions, sometimes approaching 2 cm (~1 inch) in diameter, exhibiting a series of concentric rings.
Usually, this disease develops on the lower leaves of the plant and does more damage as it moves upwards, causing potential yield loss. When this happens, it causes premature defoliation of the leaves that would normally contribute to boll development.
Areolate mildew causes small lesions to appear on leaves in the lower canopy. The lesions, 3-4 mm (~0.15 in) wide and restricted by a major leaf vein, are slightly chlorotic on the upper leaf surface with a white mildew growth on the lower surface.
Lesions may become necrotic and resemble bacterial blight. In severe cases, premature defoliation will occur. The most telling sign is the white powdery mildew growth on the underside of the leaf.
Disease Management
According to Bob Kemerait, the University of Georgia’s resident plant pathologist, both diseases can be controlled using fungicides, if farmers can find them.
“Abundant rain, high humidity and rank growth all contribute to problems with target spot and areolate mildew. It will be most important to stay on top of applying a fungicide between the first and sixth week of bloom if the conditions are wet and humid,” Kemerait said.
“If the crop is dry and suffering from drought, then a fungicide may not be needed. Scouting the crop is going to be very important this season because of the rising cost of inputs and the lack of availability for certain fungicides.”
Areolate mildew is more easily controlled by fungicides than target spot, but both need to be sprayed at the first sign of disease to stay ahead of it and gain significant control.
Kaitlyn Bissonnette, director of agricultural research for plant pathology and nematology at Cotton Incorporated says, “Understanding and developing tools to manage emerging disease threats is of paramount importance to keep cotton production profitable.”