A soybean disease that is causing more concern in Nebraska is Frogeye Leaf Spot. It is showing up more in southeast Nebraska and there is concern that it may be resistant to the Qol (Group 11) fungicide which includes Stobilirins. Quadris is a popular fungicide that Frogeye Leaf Spot has been found to be resistant to. In 2019 ten counties in Nebraska have identified soybeans that have been infected with Frogeye Leaf Spot resistant to fungicides. Research has been conducted to determine if any counties in southeast Nebraska had this resistant fungus in 2020. There was also a significant amount of SDS (Sudden Death Syndrome) in southeast Nebraska in 2020 though. If you do have soybeans that have the symptomology of SDS, you may also want to check for SCN (soybean cyst nematode), as many times if you have SDS, SCN will also be present in the soil. These two diseases have a symbiotic relationship, many times coexisting in the soil together. A disease with similar symptomology as SDS is brown stem rot. By closer examination these two diseases can be identified. If you have not had your fields tested for SCN recently, the Nebraska Soybean Board has a program that will pay for having your soil tested for SCN for free. Check with you local Extension office for sample bags. If you are in the counties of Richardson, Nemaha, Pawnee, Johnson, Otoe or Cass, contact me at firstname.lastname@example.org , (402) 274-4755 or (402) 274-9639 (cell) about sampling for SCN. I have a soil probe, that you can borrow or I can sample some fields as well. Your ag supplier may also provide this soil sampling service. If you have SDS or SCN in your soil what can you do about it? While you can not do anything this year if your soybeans have SDS, in future years, there are soybean varieties that have good resistance. There are also seed treatments available, ILEVO and also SALTRO. On-Farm research at UNL showed about a 4 bu/ac yield increase when using ILEVO compared to untreated fields. Saltro as a seed treatment for SDS has not been evaluated as much in the area. If fields have a history of SDS in soybeans, a seed treatment and the use of a resistant variety would be good strategy to consider. Finally there is a new source of resistance, PI89772 for SCN. From this source, two varieties are available, Golden Harvest GH2329X and NKBrand S23-65X. Feel free to call the number above or email the address if you have questions about soybean diseases.
Figures 1 & 2 - Plants with Sudden Death Syndrome (SDS) develop interveinal chlorosis (left) that progresses to defoliation and root rot.
Figure 3 - Lesions caused by frogeye leaf spot are small, irregularly shaped gray to brown color with dark margins.