Effect of Planting Date On Sudden Death Syndrome Foliar Symptom Severity in Iowa.

Sudden death syndrome (SDS) of soybean, caused by Fusarium virguliforme, is a relatively new disease in Iowa causing significant yield losses each year. Sudden death syndrome causes both root and foliar symptoms with foliar symptoms appearing as early as flowering. Early planting in Iowa is an important cultural practice to maximize soybean yield. However, in the southern U.S., severe SDS symptoms are associated with early planting. Research on planting date and SDS in Iowa is lacking. Our hypothesis is that growers can continue to plant early in Iowa and the yield benefit will outweigh the impact of SDS if resistant cultivars are used. The objective was to evaluate the effect of planting date on SDS foliar symptom severity and yield. To address this question research was conducted in Iowa in 2008 and 2009 at two locations with a history of SDS. The experimental design was a randomized complete block in a split plot arrangement with four replications. The main plot was planting date: late April, mid-May, and late May. The sub plot was as a factorial combination of four soybean varieties (two resistant and two susceptible) and inoculation/non-inoculation with SDS. Starting at R1, plots were visually assessed every ten days for disease incidence and severity, until plants reach growth stage R8. Data from 2008 were variable because of flooding. Inoculation did not affect SDS severity. No yield difference was observed between the first and second planting date but both yielded greater that the last planting date. No differences were observed among the cultivars. Cultivars planted early had the highest severity of SDS but there was no correlation between disease severity and yield. Research will continue in 2009 and data from both years will be presented.