12 MIN READ

Managing Mid-to Late-season Diseases in Cotton

September 2, 2019

  • Cotton should be scouted for foliar, wilt, root, and boll diseases from fruiting to defoliation.

  • Management options can be limited for controlling mid- to late-season cotton diseases.

  • Minimizing cotton stress early in the season can help reduce the severity of diseases and help maintain cotton yield potential.


Foliar Disease

Foliar disease pressure increases when a cotton crop is under stress. Mitigating stress as much as management allows can help protect the yield potential of the crop. Managing irrigation, fertility, insect pressure, and growth can reduce the probability of foliar disease. Rank growth should be controlled through plant growth regulator (PGR) applications and managing water and fertility. Crop residue should be chopped and plowed to accelerate decomposition.1

For more information about foliar diseases, refer to Mid- to Late-season Cotton Leaf Diseases.

Target Spot (Corynespora cassiicola)
 Figure 1. Target leaf spot with concentric circles.
Figure 1. Target leaf spot with concentric circles.

Symptoms

This disease typically starts in the lower canopy with small reddish spots with light and dark concentric rings.

Diagnostic Notes and Control

Usually occurs after extended periods of leaf wetness. Control rank growth through PGR and water management. Fungicides are available.


Bacterial Blight (Xanthomonas citri pv. malvacearum)
Figure 2. Bacterial blight lesions defined by leaf veins.
Figure 2. Bacterial blight lesions defined by leaf veins.

Symptoms

Small, light green, angular lesions on leaves. Bolls with round, water-soaked to brown lesions.

Diagnostic Notes and Control

Resistant varieties are available for most growing regions. Reduce rank growth and consider crop rotation.

Alternaria (Alternaria macrospora) and Stemphylium (Stemphylium solani)
 Figure 3. Alternaria leaf spot lesions with purple margins.
Figure 3. Alternaria leaf spot lesions with purple margins.

Symptoms

Small, brown, circular lesions on leaves enlarging to 0.4 inch. Old lesions have gray centers. Certain species may cause small purple spots to develop.

Diagnostic Notes and Control

Alternaria is more common in Texas and the Midsouth. Stemphylium is more commonly found in the Southeast. Attributed to potassium deficiency. Fungicides are available.

Cercospora (Mycosphaerella gossypina)

Symptoms

Small reddish purple foliar lesions that expand to light brown lesions surrounded by narrow purple margins. Old lesions may be 0.7 inches in diameter.

Diagnostic Notes and Control

Plants with moisture and nutrient stress are more susceptible to this disease. Lower yield and fiber quality can occur when part of a disease complex. Fungicides are not considered effective.

Ascochyta Blight (Ascochyta gossypii syn. Phoma exigua)
 Figure 4. Symptoms of Ascochyta blight. Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org.
Figure 4. Symptoms of Ascochyta blight. Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org.

Symptoms

Small brown foliar lesions that enlarge into irregular dead areas with dark brown borders. Lesion centers may crack and fall out.

Diagnostic Notes and Control

Can occur early in the season and enlarge over time. Usually associated with cool, wet conditions. Fungicide options are available, but generally not warranted.


For more information about wilt, root rot, and boll rots, refer to Mid to Late-season Stem and Boll Diseases in Cotton.


 
 
Sources: 
 

Newman, M.A. 2011. Cotton disease and nematode control. The University of Tennessee Extension.http://utcrops.com/cotton/cotton_images/Info24-cotton%20disease%20control-2011.pdf

2 The first 40 days. 2007. National Cotton Council of America and the Cotton Foundation.https://www.cotton.org/tech/physiology/upload/BMP_Doc.pdf

3 Wrather, A. and Sweets, L. 2009. Cotton disease and nematode management. G4261. University of Missouri Extension. https://extension2.missouri.edu/g4261

4 Texas Plant Disease Handbook. Cotton root rot. Texas A&M AgriLife Extension.https://plantdiseasehandbook.tamu.edu/problems-treatments/problems-affecting-multiple-crops/cotton-root-rot/

 

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