Cotton fungal diseases target spot and areolate mildew can cause widespread early defoliation. According to an Alabama Extension plant pathologist, the target spot is a greater threat to intensively managed cotton, particularly those with a high yield potential. Areolate mildew is a new disease in Alabama cotton, but one that can be managed.
Dr. Austin Hagan said target spot is more widespread and damaging in south Alabama, and, to a lesser extent in central Alabama, on intensively-managed cotton with a yield potential in excess of 2.5 bales per acre.
“Lint yield losses on intensively-managed susceptible cotton cultivars may reach 500 pounds of lint per acre, which translates into a farm-gate income loss at current market prices of approximately $375 per acre,” Hagan said.
Partially resistant cultivars are the preferred method of protection in central and north Alabama, particularly in rainfed production settings to avoid significant yield loss. However, fungicides do offer partial yield protection against yield loss caused by target spot.
Areolate mildew emerged as a damaging disease for Alabama cotton in 2018. Scattered, but not damaging, outbreaks were noted on Alabama Agricultural Experiment Station (AAES) research units in south and central Alabama in previous years.
Hagan said in 2018, significant premature defoliation was observed in cotton in central and southeast Alabama, with some varieties suffering noticeable damage.
Preliminary yield estimates from 2018 AAES research trials suggest yield losses may be more than 200 pounds of lint per acre. This could translate into a farm-gate loss of approximately $150 per acre.
Early and full season flex cotton cultivars and select breeding line reactions to these diseases were assessed in rainfed and irrigated settings at multiple AAES research units across the state in 2018.
Reports indicate that while there was considerable target spot development in the mid-May planted full season flex variety trial at the WREC, areolate mildew was the dominant disease noted in the later-planted early flex cotton trial.
Alabama Extension and Auburn University plant pathologists conducted studies on cotton cultivars in 2018. Studies at the Wiregrass Research and Extension Center measured damage to cotton plants by target spot and areolate mildew in early and full season flex cultivars.