Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu; @Delmarplantdoc
Soybeans grown in Delaware and Maryland can succumb to various diseases early in the growing season. These diseases typically are favored by conditions that slow soybean emergence and favor pathogen growth, such as wet weather immediately following planting. There are several pathogens that can kill soybean seedlings, but in our area Fusarium is the most commonly encountered issue, followed by Rhizoctonia. To manage seedling diseases, plant soybeans when the daily soil temperatures at the 4 inch depth average at least 65°F or more. Consider seed treatments for seed lots that have less than 85 percent germination (by the warm germination test). There are many commercial seed treatments available that may help with stand establishment, and can help improve stands in some circumstances. Treat seed with a fungicide if germination is lower than 85 percent. Seed with germination below 75 percent generally should not be treated or used for seed. Many of the newer seed treatments have low use rates and must be applied by certified seed treatment applicators. Remember that seed treatments can help with seedling emergence and provide some additional protection for about 2 weeks after planting. These products will not be effective for managing diseases that can infect roots later in growth (e.g. brown stem rot) or provide any protection against foliar diseases later in the growing season. Below is a table from the mid-Atlantic field crop disease management guide, which Dr. Hillary Mehl and myself help produce through Virginia Tech. The table provides general performance of fungicide active ingredients against some causal agents of seedlings that you may encounter. These are not commercial trade names, and some seed treatments contain multiple fungicide modes of action. The guide can be downloaded from the University of Delaware Commercial Field Crops Webpage under the “Useful Links” heading at http://extension.udel.edu/ag/plant-pathology-and-diseases/commercial-field-crops/
