Watch for Mid- to Late-Season Cotton Diseases

While good disease management practices early in the growing season help minimize plant stress, growers will need to be diligent in watching for diseases that may thrive later in the growing season. During the fruiting to defoliation stages, several diseases need to be on a grower’s radar to avoid crop damage.

Bacterial Blight

Also called angular leaf spot because of the angular appearance of the resulting lesions, bacterial blight can be found extensively in the Cotton Belt, with hotspots in the mid-South and Southeast and in the High Plains, Rolling Plains, Southwest Oklahoma and along the Texas Gulf Coast. Humid weather and heavy field irrigation provide conditions that are conducive for this disease.

Symptoms include small, dark green spots, which are first visible on the underside of leaves and later on the upper leaf surface. Lesions can also extend along the main leaf vein. Leaf petioles and stems may become infected and cause premature defoliation. Black cankers may encircle the stem or branches, causing these portions to die above that line. If bolls become infected, boll rot can result in rotted seed and discolored lint.

Bacterial blight
Bacterial blight. Photo courtesy of Clemson University - USDA Cooperative Extension Slide Series,
target leaf
Target leaf spot

Target Leaf Spot

Target leaf spot (Corynespora cassiicola) has been identified in the Eastern Cotton Belt. Warm, humid conditions favor the development of this disease. According to University of Alabama Extension research, lint losses from target spot have been estimated at 200 lbs. per acre.

However, the later in the season damage occurs the less impact it has on yield.

Symptoms first develop as red dots that lead to the formation of irregular to circular lesions with tan to light-brown centers. Lesions further enlarge into a target-like appearance formed from concentric rings within the spot. Heavy infection can cause premature defoliation along with yield loss.

Verticillium Wilt

Verticillium wilt has become one of the most economically significant diseases in some cotton-growing regions. The disease causes substantial yield and fiber losses when infections are severe. Reductions of greater than $400 per acre in net returns can occur, according to Texas A&M research.

Verticillium wilt can occur across the entire Cotton Belt; however, is most common in the lower Mississippi Valley, the High Plains and the Southwest. It can be particularly devastating in irrigated areas of the Southwest. Leaf symptoms and yield damage can vary according to variety, fungal isolate, developmental stage and environmental conditions.

Early leaf symptoms include chlorosis, a yellowing of leaf tissue caused by a lack of chlorophyll, between the veins. Verticillium wilt can malform younger bolls; severely stunt plants; and cause premature defoliation, yield loss and reduced fiber quality.

Verticillium wilt. Photo courtesy of Clemson University - USDA Cooperative Extension Slide Series,

Managing Mid- to Late-Season Diseases

Although management efforts can help reduce the incidence and impact of bacterial blight, target leaf spot and Verticillium wilt, no single approach is highly effective to completely control these common diseases of cotton. Thus, a combination of preventative measures for managing cotton diseases is key, including scouting, cultural practices, variety selection and fungicides.

Bayer Solutions for Managing Cotton Diseases

In addition to best management practices for cotton, seed varieties can help manage disease resistance and increase success.

For example, Stoneville® 4946GLB2 and FM 2011GT and FM 1911GLT provide good resistance to root knot nematode/Fusarium wilt, while several FiberMax® varieties have the best tolerance in the industry to Verticillium wilt, for which no chemical controls are available. These options include FM 2322GL, FM 1830GLT and FM 2334GLT. Additionally, Bayer has several FiberMax and Stoneville varieties that are resistant to bacterial blight.

Proline® fungicide fights foliar diseases such as target spot present at application and stops new infections from attacking crops.

View our products section to learn more about the portfolio of products from Bayer to help you manage disease in your cotton crops or contact your local Bayer representative.

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