Evaluation of Current Soybean Production Practices on Phomopsis Longicolla Infection.

Phomopsis longicolla is a common pathogen in the United States that negatively affects soybean [Glycine max L. (Merr.)] quality and yield. Previous studies suggest that management practices such as foliar fungicide applications and seed treatments provide the best control of this pathogen. Unfortunately, many of the products used in these studies are no longer available for use on soybean. This has created a need for further investigation of how various management practices affect the epidemiology of this pathogen in order to provide swift and adequate control for soybean growers. The objectives of this study were i) to evaluate the effect of nine management treatments composed of different combinations of row spacing, foliar fertilizer, soil-applied fertilizer, plant population, foliar fungicide, seed treatment, and inoculant, and ii) to determine what regions in the United States have the highest incidence of  P. longicolla infection in seed. This study was conducted as a randomized complete block design with four replications at three locations each in Michigan, Minnesota, Iowa, Kentucky, Arkansas, and Louisiana in 2009. Treatments were applied during the growing season and seed was collected at harvest. The seed underwent a warm germination test, accelerated aging test, and a culture plate test to determine viability, vigor, and percent P. longicolla infection of the soybean seed. Preliminary results indicate that the southern region (Arkansas, Kentucky, and Louisiana) has a higher incidence of seed infection by this pathogen than the northern region and foliar fungicide applications at the R3 or R3 and R5 growth stage appeared to reduce P. longicolla infection levels. This study will continue in 2010.