By Clint Thompson
It may be early in the cotton season, but Georgia’s growers need be concerned with potential disease buildup amid the increased rainfall across the region.
The Georgia Cotton Commission and University of Georgia (UGA) Extension Cotton Team caution producers about areolate mildew and target spot. Bob Kemerait, UGA Extension plant pathologist, discussed both diseases in the team’s June newsletter.
“We do not need to worry about target spot or areolate mildew until the cotton begins to bloom, and likely not until several weeks after first-bloom,” Kemerait noted. “However, because both diseases can easily take yield from a cotton crop and because fungicides are often used to protect against yield loss, it doesn’t hurt to begin to prepare now for a fungicide program that may be deployed later.”
Kemerait emphasized that “later” refers to no earlier than first-bloom for all cotton farmers and not until target spot is found or areolate mildew is reported for most growers.
Areolate Mildew
Kemerait stressed that areolate mildew can be problematic for cotton growers across the Coastal Plain, though it has been historically confined to Southeast Georgia, east of I-75. Based upon recent research, the same fungicides used to control target spot can be implemented for the management of areolate mildew.
Azoxystrobin has been an adequate fungicide for areolate mildew, but fungicide resistance has developed in some locations in recent years. Growers who are within four weeks of defoliating their cotton do not need to worry about managing areolate mildew. Fungicides should only be used when defoliation is more than a month away and weather is favorable for the spread of the disease.
Target spot
Target spot is important to manage since significant defoliation can occur within two weeks after the first spots are observed if favorable conditions exist. Boll development can be impacted when pre-mature defoliation removes the leaves feeding the younger bolls.
Kemerait said that target spot is most likely to affect a crop when conditions such as irrigation, rainfall and soil fertility produce lush plants with substantial canopies. When applying fungicides, it is important to ensure that sufficient spray coverage is applied deep in the canopy.
UGA Extension advises growers to scout their cotton crop at the approach of the first week of bloom and check the lower canopy for symptomatic leaves. If target spot is not observed, growers can delay a fungicide application and scout again in the upcoming weeks. The best fungicide timing is usually during the third week of bloom.
Priaxor is the most important fungicide in managing target spot. Headline and Miravis Top are also effective.