Quick and Dirty about Target Spot in Cotton

Author: Heather Marie Kelly, Extension Plant Pathologist 1 Comment

Some additional images and recommendations on identifying and managing target spot in cotton…

To summarize from previous articles on target spot in cotton (Don’t let bacterial blight fool you and Target Spot in Cotton – How to identify it and management options on news.utcrops.com):

Identification of Target Spot

  • Lesions have concentric rings, with or without a yellow halo, first appear in the lower canopy (Image 1 and 2)
  • Target spot is observed where the canopy has closed, not on edge of field or thin cotton (image 3 and 4)
  • Defoliation starts in the lower canopy, leaves with 3 or more lesions may turn yellow and fall (image 5)
  • Additional information/images of target spot and other leaf spots of cotton, as well as a key to differentiate between leaf spots can be found on the mobile friendly guide at guide.utcrops.com.

Management

  • 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 (image 6)
  • Fungicide timing – It’s better to err late than early. While fungicides generally work best as preventatives that is not the case with target spot in cotton. Research shows it is best to wait to apply fungicide until you see lesions in the lower canopy which is usually 2 to 3 weeks after canopy closure/3rd week of bloom (depending on plant date and weather). Fungicide applications applied after physiological cutout (NAWF 5) may decrease defoliation but are not recommended because they will often fail to protect yields.
  • Fungicides labeled for target spot in cotton include: Elatus (5-7.3 fl oz/a), Headline (6-12 fl oz/a), Priaxor (4-8 fl oz/a), Quadris (and generic azoxystrobin products, 6-9 fl oz/a), Stratego YLD (5 fl oz/a), and Twinline (7-8.5 fl oz/a). From Regional data Priaxor (4 fl oz/a) and Headline (6 fl oz/a) have most consistently reduced defoliation and protected yield from target spot.
  • One well timed fungicide application or one application followed by a second application 2 weeks later may be recommended to reduced defoliation and protect yield. Decisions about fungicide applications need to be made on a field by field basis and are dependent upon disease development, weather/irrigation, variety, canopy management, and other factors that could influence disease development (i.e. plant population, fertility rate, row spacing, etc.)
Image 1 – Target spot in lower canopy
Image 2. Circled leaves have target spot lesions
Image 5. Yellowed leaf with target spot lesions
Image 3. Closed canopy where target spot may be found in lower canopy
Image 4. Field variability – thin areas without target spot, thick areas where the canopy has fully closed is were target spot will be developing
Target spot on leaf and bracts
Defoliation of lower canopy due to target spot
Image 6. Target spot on left, leaf spot complex (Alternaria, Stemphylium, and/or Cercospora) on right
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