Symptoms of bacterial blight have been observed on cotton plants in many southeast Missouri fields during the last 14 days. The symptoms are black, angular-shaped spots on the leaves. The spots are slightly smaller than a pencil eraser, and the angular shape is the result of small veins in the leaf limiting bacterial movement in the leaf. The lesions are visible on both sides of the leaf but are more pronounced on the upper side. The diseased tissue will remain black, and the infected leaves may defoliate if infection is severe. This disease can’t be managed at this stage by treatment of the plants with a bactericide or fungicide. However, farmers can take action to minimize spread of this disease by use of growth regulators to restrict plant growth. This will allow air to better circulate through the canopy, and this is good since this disease will spread more rapidly in rank-growth cotton. This action should be taken now to minimize the spread of this disease to bolls because bacterial blight can cause boll rot.
This disease is caused by bacteria, and it was a problem in many cotton fields in the U.S. until the late 1970’s when seed companies began acid delinting seed. This process killed the bacteria the survived on the seed. I am not sure why this disease has developed this year. You may contact me for more information.
Allen Wrather (573-379-0259)