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Funded Project

Funding Program: IPM Enhancement Grants

Project Title: Managing target spot, caused by Corynespora cassiicola, in cotton

Project Director (PD): Austin Hagan [1]

Lead State: AL Lead Organization: Auburn University

Cooperating State(s): Georgia

Undesignated Funding: $30,000

Start Date: Jan-01-2014 End Date: Dec-31-2014

Pests Involved: Target spot

Site/Commodity: cotton

Area of Emphasis: plant pathology

Summary: Impact of the emerging foliar disease target spot incited by the fungus Corynespora cassiicola on cotton lint yield and quality will be assessed as we develop integrated disease management strategies. Target spot, which was restricted to irrigated cotton in southwest Georgia, in the past two years has caused widespread defoliation of cotton in Alabama, Georgia, North Carolina, South Carolina, and Virginia. Target spot damage is higher in intensively-managed cotton. Frequent showers and irrigation favors disease development, while symptoms are minimal in later-planted cotton. Estimated disease-related yield declines in irrigated cotton in Georgia are 200 to 600 lb lint/A, while recent Alabama studies noted losses of 20% on a susceptible as compared with 5% for a tolerant variety. A target spot-incited yield decline of 5% would cost the Alabama and Georgia economies $65 million. Presently, control options are limited due to the lack of information on fungicide efficacy as impacted by application timing, number, and placement along with planting date, plant populations, and variety reaction on boll retention and yield. We propose to assess the efficacy of registered fungicides in preventative and on-demand programs on target spot susceptible and tolerant varieties as impacted by application timing, number, and placement, assess core commercial variety reaction to target spot and fungicide inputs, as well as the impact of planting date and seeding rate on target spot intensity and yield of core varieties. Efforts to define yield losses in susceptible and tolerant cotton varieties and the economic value of fungicide inputs from the Gulf Coast to Tennessee Valley cotton production regions in Alabama will continue. Studies will be conducted at research units and as large scale replicated demonstrations in farmer cooperator fields. The latter studies will be done by regional or county extension personnel to develop local data concerning variety performance along with fungicide efficacy and used as sentinel plots for timely disease alerts, local tours, with educational materials being distributed to clientele via twitter or other social media. Our results will provide a base from which to develop a target spot management program for the southeastern cotton production region. Objectives: 1. Determine the impact of target spot on the lint yield and quality indicators of target spot susceptible and tolerant cotton varieties at multiple locations. 2. Evaluate the reaction of a core of commercial varieties to target spot on rainfed and irrigated sites over a wide geographic area of Alabama and Georgia. 3. Establish the efficacy of registered fungicides along with broad-spectrum fungicide partners as influenced by application timing, number, and placement on a susceptible and tolerant cotton variety. 4. Assess the impact of seeding rate (plant population) and planting date on target spot development and yield response of selected core commercial cotton varieties. 5. Conduct extension related activities including on-farm replicated fungicide and variety evaluations conducted by county and regional extension agents with Co-PI coordination.

Final Report:

Impacts Cotton acreage in Alabama and Georgia totaled approximately 340,000 and 1.35 million, respectively, in 2014. Target spot incited by the fungus Corynespora cassiicola is an emerging disease in cotton and an established disease in soybean, sesame, tomato, cucumber, and container-grown ornamental crops. Presently, target spot control options are restricted due to limited information concerning fungicide efficacy as impacted by application timing, number, and placement along with tillage practices, crop rotation, planting date, plant populations, and variety sensitivity. Control failures due to resistance in the causal fungus C. cassiicola have been reported in vegetables for the strobilurin fungicide, azoxystrobin (Quadris®), which is one of two strobilurin a.i. registered for target spot control in cotton. In Georgia, disease-related lint cotton losses are estimated at 200 to 600 lb lint/A ($120 to $360/A at the current world cash price of $0.60). In 2013, farm gate revenue losses due to target spot in Alabama, Florida, and Georgia ranged from $50 to $80 million. Disease related yield losses to target spot were much lower in Alabama. In Alabama field studies in 2012 and 2013, yield protection from the above fungicides with a cost of $30/A ranges from 100 to 300 lb lint/A, which translates into an income recovery of $60 to $180/A at the current world market price of $0.60. Due to a variety of factors, including relatively dry August summer weather patterns, losses to target spot were greatly reduced in 2014 as compared with 2013. In addtion, widespread production of target spot tolerant varieties, which was empahsized in 2014 production meetings and extension literature, contributed to the reduced disease-related losses in 2014.

Outcomes Target spot is an emerging disease of cotton in the southern cotton production region. Highest risk of significant disease related yield losses are in the southern third of Alabama and Georgia along with the Florida Panhandle, particularly in intensively managed, irrigated cotton. Based on observations in farm fields and field trials, disease activity is insufficient, particularly in the northern third of Alabama, to result in significant yield loss. This observation suggests that target spot is unlikely to cause appreciable yield loss in cotton produced in Arkansas, Mississippi, Missouri, North Carolina, South Carolina, and Tennessee unless certain weather parameters are met. The critical short term impact of this project is improved crop consultant and grower recognition of symptoms of target spot, management inputs that may influence disease severity, and the need and possible impacts of fungicide inputs on crop yield and quality. These and other topics relating to target spot have been presented at local, regional, state, and national meetings to cotton growers, crop consultants, and other agribusiness personnel as well as extension and research personnel from Alabama, Georgia, and neighboring states. The above information on this and other diseases of cotton was also disseminated using electronic media such as twitter (15), U-Tube (4 videos), and extension publications (AL Timely Information, GA Cotton Crop Production Guides, AL IPM newsletter). Primary medium term programmatic impact would be an increased emphasis on scouting for disease and response with fungicide inputs in at-risk situations when losses are most likely to occur rather than blanket preventative fungicide treatments. This approach will be much more important in 2015 following the reduction in cotton prices to the $0.60 per pound and limited profit potential. Growers have been encouraged to monitor local or regional cotton variety trials and sow those varieties that are not at risk for significant target spot-related yield loss or require significant fungicide inputs. Growers were surveyed at 3 county cotton production meetings in SW AL in January 2015. Of the surveys completed, 78% were from cotton producers and the remainder was from crop consultants. Average cotton acreage per cotton producer was 616 acres. Deltapine 1137 and Deltapine 1028 accounted for nearly 35% of the total cotton acreage while the target spot susceptible variety Phytogen 499 was sown on a much small acreage than was noted prior to the 2014 production season. Among the growers surveyed, 44% scouted their cotton for target spot and all of those individuals made at least one fungicide application to approximately 78% of their cotton acreage. Headline 2.09SC, Twinline, and Quadris 2.08SC were used in equal proportions. All of the growers that applied a fungicide saw a noticeable yield gain. Crop consultants (44%), extension personnel (56%), and industry new/publications (33%) were the primary sources of information concerning target spot control. A potash deficiency was also noted by 44% of cotton producers surveyed.

Report Appendices 3073040_0000001.pdf [PDF]

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