Now is the time when you should be on the lookout for seedling diseases in corn and in full season soybeans. Seedling diseases can be categorized as either pre-emergent or post-emergent. Pre-emergent seedling diseases kill the seedling soon after germination or before it can reach the soil surface. Some potential indicators of pre-emergent seedling disease issues include poor stands in low lying or poorly drained areas of the field or overall poor seedling germination. Post-emergent seedling diseases can kill the seedling soon after emergence.
Sometimes plants can tolerate post emergent diseases and do not die, but may instead be stunted or yield less than healthy plants. Such plants may prone to drought related injury as a result of compromised root systems. Many times seedling diseases develop as a result of some other stressful event that predisposed the plants to infection. Good examples of such events include planting into cool soils, planting too deep, flooding, and misapplication of fertilizer and/or pesticides.
There are several fungi that can infect the roots of corn and soybean seedlings. Examples include Pythium, Fusarium, Rhizoctonia, and Diplodia (found on corn only). To distinguish plants suffering from root rot from those suffering from abiotic issues, such as poor nutrition, check the root systems. Plants suffering from root rot typically contain roots and root tips that are mushy, and brown to grey in color. As mentioned previously, seldom are seedling diseases only the result of a pathogen. Many times other factors are the real culprit, allowing these fungi to take over. The best way to reduce seedling diseases is to plant at the correct depth into well prepared, warm soils (above 55°F). Treating seed with a fungicide seed treatment can provide some additional protection. There are innumerable fungicide seed treatments nowadays, and it can be difficult knowing what a given product contains. The University of Wisconsin published a nice guide showing many of the seed treatments for corn and the various active ingredients they contain.