Evaluation of Inoculum Dispersal in Soybean Production Systems.

Frogeye Leaf Spot (FLS) was first reported on soybeans in the United States in the mid-1920’s. FLS is most commonly found in the southern region of the U.S. where warmer temperatures and high humidity are favorable for disease. FLS is caused by the fungal pathogen Cercospora sojina K. Hara. C. sojina is predominantly a foliar disease; however it can infect the seeds, pods and stems. FLS survives in soybean residue and seeds. It is presumed that the spores produced by the fungal pathogen are dispersed by wind and/or splashing rain. The following trial was conducted to investigate if one mechanism of inoculation was more prominent than the other which could influence disease management practices. The study was conducted in Milan, Tennessee at the Milan Research and Education Center in a field that has been in continuous, no-till soybean production over ten years. The field has a history of high FLS pressure. The experimental design was a randomized complete block with 4 replications using 30 ft. (9.1 m) by 10 ft. (3 m) plots. The trial included three treatments and a nontreated check. The first treatment excludes wind dispersed spores by using 3 transparent plastic cages that surround 5 ft. (1.5 m) of the center 2 rows. The second treatment excludes rain splashed dispersal by lying a black tarp between the rows. The third treatment excludes both splash and wind dispersal, using both the cages and the tarp. Weekly disease ratings were taken at reproductive stage R1 (bloom) until R8 (maturity). Assessments include the correlation between disease and yield and treatment effect on disease development using area under the disease progress curve.  Results and conclusions from the study will be discussed.