By Ryan Adams
In 2018, the southeastern U.S. produced an estimated 5.6 million bales of cotton, or 30 percent of the U.S. upland crop of cotton. An emerging challenge for growers is target spot, a disease caused by the fungal pathogen Corynespora cassiicola. Target spot has only recently become a threat to cotton, but is an established disease in soybean, sesame, tomato, cucumber and container-grown ornamental crops. Little is known about how C. cassiicola spread to cotton crops, where it came from initially, or how likely it is to affect cotton yield from year to year. While the initial report of target spot on cotton was in southwest Georgia, it has now been reported in Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, and Virginia.
Yield losses have a potential to be as high as 400 lbs. of lint per acre. More data about target spot distribution across eastern U.S. cotton acreage and disease onset are needed to understand disease development and potential impact on yield. Consistently effective IPM practices (such as canopy management and fungicide application) are limited due to a dearth of epidemiological information on target spot disease. Furthermore, there are no highly resistant cotton varieties.
Symptoms of Corynespora cassiicola:
The Southeast Cotton CPP aims to contribute to a better understanding of target spot among producers and investigate potential impacts of growing practices on pathogen development and disease onset. This educational and research work is the prerequisite for more consistently effective IPM practices for target spot management. This process will also help identify other problematic foliar diseases and generate distribution and risk data to inform growers on their management.
In 2017, bacterial blight was commonly misidentified as target spot, so the CPP focused on educating growers on correctly identifying both bacterial blight and target spot. In 2018, the CPP Coordinator, Dr. Heather Kelly, distributed a cotton IPM survey that collected information from 36 participants that self-identified as managing or influencing 46% of all cotton acreage in Tennessee. In general, the results found that 86% of growers surveyed deploy some type of control strategy for pest management and 89% regularly scout throughout the season for pest problems. Dr. Kelly said, “It was nice to see that our IPM efforts were not going to waste in Tennessee. Almost 90% of cotton acreage in Tennessee are being managed with great IPM practices …the program didn’t turn out the way we initially set out, to gain further insight into target spot. As it turns out we didn’t see as much target spot as we thought we would, but we saw more bacterial blight and other target spot ‘look-a-like’ diseases. It ended up being a great educational opportunity on correct disease identification and how that has a huge impact on management strategies.”