Are soybean foliar fungicides worth it?  - 2010-06-16

Since 2004, we have studied the effect of foliar fungicides in replicated trials across the state. The first set were full field scale trials. Producers or dealers applied the fungicide at R3 and harvested the study. We scouted the field prior to fungicide application, 2 weeks after and just before maturity. In 28 trials, there were no aphids to complicate the results and 6 had significantly higher yields than the nontreated controls.  However, only 3 of these recovered the cost of the fungicide application.  In these 3 instances, frogeye leaf spot was present at the time of application. When aphids were present, the insecticide alone was the driving force and there was no added yield benefit when the fungicide was added.

In another related study, we examined the effect of the R3 fungicide application on brown spot. Brown spot is caused by the fungus, Septoria glycines, and is usually found in the lower canopy. We have seen the disease present as early as the unifoliate stage and most often contributes to early defoliation of the lower canopy. All of the fungicides we evaluated were effective in reducing the severity of brown spot on the lower canopy. However, there was very little yield gain, on average only 3 bu/A.  Brown spot is truly a minor disease.

The first find of Soybean rust in the US was on June 10th in Texas on the border with Mexico,  It will take many more weeks for this to be found in other states as the weather has not been favorable in the south for spread and development of the disease. Current predictions for the states in the southern US are they won’t begin to detect it for another 4 weeks at the earliest. For Ohio, we are at very low risk for soybean rust to develop in Ohio during 2010 growing season.

The weather conditions over the past few weeks are very similar to last year.  If it stays cool and wet, then white mold will be the next issue to monitor.  One hot dry week close to flowering, where the top 2 inches of soil dries out, will knock this one out of contention as a problem.