Ed Seymore, TAREC Ag Technician who is scouting fields for brown marmorated stinkbug (BMSB), aphids, kudzu bug, etc., reported to me today that every soybean field that he is checking west of I95 in Virginia (He’s in the Shenandoah Valley today) has frogeye leaf spot. Some fields are heavily infested (all leaves; up to 20-25 spots per leaflet).
I called this to your attention earlier this year, as I was seeing frogeye leaf spot symptoms in several variety tests. Many of our varieties have resistance to the disease, but some do not. In addition, the level of resistance varies with variety. The disease will also be worse in non-rotated fields (continuous soybean). In the past, I’ve found that varieties with good resistance truly resist the disease. Varieties with moderate resistance tend to hold up pretty well if soybean are in rotation. In rotated fields containing a susceptible variety, the disease can be severe but not devastating. But, the disease can devastate soybean varieties with no resistance when these soybean are following soybean (see photo below from non-rotated field planted to susceptible variety).
So, be sure to scout your soybean fields for this disease. Symptoms are round spots with tan/grey centers and reddish halos around the spot. I have no good threshold for treatment, but if you have a susceptible variety and/or are growing soybean after soybean, a fungicide application is in order. If you have not already applied a fungicide, I’d also suggest using a fungicide that combines a strobilurin with a “curative” fungicide. Combination products that have performed well on other disease, but not necessarily on frogeye leaf spot (frogeye has not been a big problem in the recent past) in Dr. Pat Phipps tests include: Priaxor, Quilt XL, Stratego YLD, and Quadris Top.