Field trials were conducted at different sites across Kentucky in 2019 to evaluate the effectiveness of different management practices for important soybean diseases that affect Kentucky soybean farmers (frogeye leaf spot, target spot, southern stem canker, and soybean cyst nematode).
The fungicides Lucento, Miravis Top, and Revytek were found to be the most effective in reducing frogeye leaf spot in a trial conducted at Union County, KY. Since the frogeye leaf spot pathogen is resistant to strobilurin fungicides in Kentucky (and across the soybean production region in the U.S.), it is important to identify which fungicides are the most effective in managing frogeye leaf spot. All three of these fungicides contain two active ingredients that belong to chemistry classes besides the strobilurins, which are the triazoles and the SDHIs. It is important that farmers choose products that contain at least two effective fungicide active ingredients to manage frogeye leaf spot and to help slow down resistance to other chemistry classes.
The fungicide treatments Headline, Priaxor + Tilt, Lucento, Topguard EQ, and Miravis Top were found to be the most effective in reducing target spot in a trial conducted at Princeton, KY. Target spot is a relatively new disease to Kentucky, but incidence appears to be on the increase. Some soybean varieties are very susceptible to target spot, so it is important to know which fungicides have efficacy against this disease in case a susceptible variety is grown. At this time, most companies do not provide ratings for target spot resistance for their soybean varieties. Strobilurin fungicide resistance in the target spot pathogen has been reported in Alabama, but we have not yet detected strobilurin fungicide-resistant strains of that pathogen in Kentucky, but it is likely a matter of time before we do. From our trial, it appears that strobilurin fungicides are still effective for managing target spot in Kentucky for now, since Headline did reduce disease. Similar to what has been reported in other states, we found that products that contain an SDHI fungicide, tend to provide better control of target spot (i.e. Priaxor, Lucento, and Miravis Top).
In a trial that evaluated different fungicides and application timings on a southern stem canker-susceptible and -resistant variety at two locations in Kentucky (Caldwell and Daviess Counties), it was found that fungicides had little effect on southern stem canker, and that the resistant variety outperformed the susceptible variety at both locations. As observed in our research, southern stem canker can be a very damaging disease when susceptible varieties are grown. Unfortunately, our research showed that if a susceptible variety is grown, that a foliar fungicide application is not likely to protect it from losses due to stem canker. Farmers that have had problems with southern stem canker in the past, should grow resistant varieties as their first layer of defense against that disease.
In a trial that evaluated different seed-applied nematicide treatments across 9 locations in Kentucky (4 locations with no detectable soybean cyst nematode and 5 locations with soybean cyst nematode), no improvement of plant stands or yields were observed. Other researchers have reported a high level of variability in their results with seed-applied nematicides on soybean. For management of soybean cyst nematode, farmers should use crop rotation and resistant varieties as their first lines of defense. Seed-applied nematicides may provide benefits in certain situations, and more research is needed to evaluate these treatments over at least one more growing season.