Identification and Management of Leaf Spots in Cotton

Author: Heather Marie Kelly, Extension Plant Pathologist Comments Off on Identification and Management of Leaf Spots in Cotton

This year I have gotten more questions about leaf spots in cotton than any other.  It hasn’t always been clear which leaf spot is present, but the following resources can help identify and understand management options of leaf spots in cotton.

This season in cotton bacterial blight is the leading leaf spot culprit, but as canopies have been closed in some fields for over 2 weeks and have had good moisture, target spot might start showing up more often as well as other leaf spots. Use the resources below to identify what leaf spots you’re seeing and what the best management options are:

Main points to remember about Target Spot that can help distinguish it from other leaf spots:

  • Leaf spots begin in lower canopy, will be in rankest growth where the canopy is closed, not on the edge of a field or thin cotton
  • Lesions have concentric rings, with or without a halo, and are circular. If bacterial blight is present in the field and target like lesions are more angular and found in middle to upper canopy, then the lesions are bacterial blight
  • Target spot is the only leaf spot in cotton that responds to fungicide and a fungicide might be recommended to protect yield. Hence, IT IS VERY IMPORTANT to clearly identify target spot from other leaf spots. Fungicide is best applied ONLY AFTER identifying target spot in the field – if there is no target spot then applying a fungicide is not needed.
  • Additional information can be found in previous articles at news.utcrops.com (most recent article: Quick and Dirty about Target Spot)
Target spot on leaf and bracts
Defoliation of lower canopy due to target spot
Bacterial blight angular lesions with yellow halo. Background leaf with additional bacterial blight.
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