Spotting and managing target spot

To hear first-hand from an expert about how to manage target spot and some results of research to help, tune in next Monday afternoon at 3 PM for Dr. Austin Hagan’s webinar on target spot. Click here to register.

From an article by Tyson Raper, University of Tennessee, in Cotton Grower

As the cotton specialist for the state of Tennessee, I am constantly on the lookout for potential issues that may impact Mid-South cotton production. Over the past several years, I have occasionally observed several “target spots,” or Corynespora leaf spots, on the lower leaves of rank cotton plants. Although the number of spots and number of affected leaves are typically low, many growers have asked if the disease might be able to cause the 200-400/lb lint per acre yield penalties reported along the Gulf coast.

Before we get to that question, let’s cover some background on the disease.

Target spot is occasionally observed in cotton plants which have experienced excessive canopy humidity. Caused by the fungus Corynespora cassiicola, it has been reported in almost every cotton-producing state within the Southeast and Mid-South in the past three years. Target spots are typically found on mature main stem and subtending leaves close to the plant base. This disease was dubbed target spot due to the irregular concentric rings contained within the dark brown to light brown lesions. Although lesion size and number per leaf can vary substantially, lesions are commonly larger than 1/4-inch in diameter. Affected plants will also prematurely shed mature leaves starting from the base of the plant as the disease progresses.

The disease is most common in fields with excessively tall cotton due to inadequate plant growth regulation and/or excessive nitrogen, very high levels of canopy humidity from overhead irrigations or frequent rainfall events (like we experienced in late July and early August), large amounts of cotton residue common in continuous cotton rotations, and late maturing, tall-growing varieties.

Fortunately for producers along the northern edge of the Cotton Belt, this disease is currently in the crosshairs of several regional Cotton Incorporated projects. One of the field crops pathologists currently working on the disease is Dr. Heather Kelly with the University of Tennessee. From her research, Tennessee has initially been predicted to be at low risk to target spot, since Tennessee’s environment is not generally conducive for early onset and rapid disease development.

Read more in Cotton Grower.

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