Update on Cotton Diseases: Target Spot and Aerolate Mildew

Source: Dr. Amanda Scherer, Extension Plant Pathologist for the August 17th edition of Cotton Shorts

 

High humidity and temperatures along with vigorous canopy growth will favor prolonged periods of leaf wetness in crops and drive disease pressure across Alabama in August. In cotton, target spot has already started to appear in Central and South Alabama. Symptoms first appear in the lower canopy and include visible lesions that are light to dark brown necrotic spots with concentric rings (figure above, left); hence, the name “target spot.”  Producers should be proactive by scouting their cotton fields routinely for target spot to make management decisions. Timely fungicide applications will reduce target spot severity and will offer yield protection, especially in high-yielding cotton. Fungicides can be applied for target spot between the first and sixth week of bloom using the following recommendations:

1. Based on growth stage starting at 1st or 3rd week of bloom followed by another application at the 3rd or 5th week of bloom, respectively.
2. Or at first sign of disease followed by a second application as needed.
3. Or at first sign of defoliation followed by a second application as needed. However, target spot can be very difficult to control with fungicides if 25 to 30 percent of the leaves are already gone due to premature defoliation.

Areolate mildew, which is easily recognized by the appearance of white mildew growth covering parts of or entire leaves (figure above, right), has also been reported in Elmore and Escambia Counties. Symptoms first appear in the lower canopy and move upwards similarly to target spot. Fungicides should be applied at the first sign of disease followed by a second application as needed. Priaxor at 4 to 8 fl. oz., Revytek at 8 to 12 fl. oz., and Miravis Top at 13.6 fl. oz. are all great options for target spot and areolate mildew. See the Alabama extension publication, “Cotton IPM Guide” for more information on recommended fungicides to control target spot and areolate mildew.