This was a very challenging year to conduct research. The challenges that occurred at planting, delayed planting, heat during the season, and then more rain right before harvest led to a tough year. With these conditions it is challenging to assess what the affects on stand or yield were from the pathogen, the treatments we applied or what was just due to weather. Across the nine different fields that we had plots in this summer, variation is the rule and it is making it very difficult to point changes in yield directly at the treatment.
Here is a brief list of what the OSU Soybean pathology lab evaluated this past summer for Ohio producers: Efficacy of seed treatments towards key seed and seedling pathogens (Rhizoctonia, Fusarium graminearum, Fusarium virguliforme, Phytophthora sojae, Pythium spp.); efficacy of seed treatments on the changes in SCN populations; evaluation of planting SCN resistant varieties on changes in SCN populations and root pathogens associated with high SCN populations; evaluation of the sudden death syndrome differentials to Ohio fungal populations; effect of resistance and rate of active ingredient for management of Phytophthora damping-off; effect of seeding rate on late planted soybeans with high rate of seed treatment; as well as the effect of fungicides for management of Sclerotinia white mold. This work was done with the awesome assistance of county educators Alan Sundermeier, David Dugan, Bruce Clevenger, producers in Defiance, Wood, Pike, and Brown Counties; OARDC research staff, funding from soybean check-off dollars to Ohio Soybean Council, North Central Soybean Council, OARDC, and numerous companies. Over the next few series of articles we will take a look at the results from 2011.
a) Sudden Death Syndrome. This fungal pathogen infects roots early in the growing season during wet conditions. However, symptom development does not typically occur until the plant reaches the end of its reproductive phase, unless inoculum levels are high, and weather is especially favorable. This past season we planted a set of lines that were identified in Illinois as susceptible, moderately susceptible, resistant and highly resistant to this fungus. The location used also has soybean cyst nematode, which is another key pathogen that when SCN and the SDS fungus are both present, symptoms of SDS become well developed. Symptoms of SDS developed prior to flowering this year in the field. This was due to the continued heavy rains shortly after planting. Areas of the field with very high populations of SCN were stunted. Each of the lines developed symptoms of SDS similar to the resistance score for what has been reported from other studies. Within the north central soybean research program, there is a team that evaluates germplasm annually for resistance to SDS. The results of these studies indicate that we can readily use the results from the Illinois trials to make decisions here in Ohio.
b) Rate of seed treatment. We evaluated the rate and efficacy of numerous seed treatments this past year. For the vast majority of these trials, there was no significant difference in 2011. When we could get into the fields, conditions were typically very good with warm, dry soils. Our irrigated field study, at Northwest branch, showed resistance levels to P. sojae in the variety was the most important factor this year. We evaluated the 0.16, 0.32, and 0.64 fl oz/cwt of Apron XL on Sloan (moderate partial resistance), Conrad (high partial resistance) and Kottman (Rps1k, Rps3a plus high partial resistance). Fungicides had no effect this year on early stand or yield at two locations (P>0.3). However variety was highly significant (P<0.0001) for final yields. Yields of Kottman were greater than Conrad which was greater than Sloan. Resistance to P. sojae provided from 30 to 65% more yield in the resistant varieties compared to the susceptible variety at these two locations in 2011. We have shown over a number of years that seed treatments will be effective in reducing the impact of damping-off, but that the best resistance package of an Rps gene combined with high levels of partial resistance provides consistent performance over years.