Diagnosing early soybean stand losses

By Stephanie Karhoff, Ohio State University Extension Field Specialist
Early season scouting sets the stage for a successful crop but determining the culprit(s) behind stand losses can be difficult. Cool temperatures, planting issues, soil crusting, seed, and seedling disease, herbicide damage, and insect injury can all cause delayed emergence and thin stands. The key is to scout early and identify the issue before replanting or making other management decisions.

When scouting fields, first ask yourself if the problem is occurring in a pattern or scattered randomly through the field. For example, do thin stands correspond to low-lying or poorly drained areas? This may indicate flooding injury or damping off from fungal-like pathogens like Pythium and Phytophthora spp. that thrive in wet conditions. Next, consider recent weather and soil conditions. A heavy rainfall event followed by a warm, dry period can cause soil crusting, reducing stands and plant vigor. Next, assess individual plants throughout the entire field. Walk the field in a “Z” or “W” shaped pattern and stop every “x” number of steps to examine 5 to 15 plants until a minimum of 50 to 100 plants per field are assessed. (Of course, deviate from this scouting pattern as necessary to check out potential problem areas.) For each plant, record the growth stage and observe any symptoms like plant yellowing or discolored root tissue. Dig seeds or plants up with a spade or hand trowel in problem areas and check for planting depth, seed placement, sidewall compaction, or rooting issues.

Table 1 from the Crop Protection Network includes common issues you may encounter during the seed or seedling stage for soybean. This list is not exhaustive, and many of these can occur simultaneously in a field. I’d also encourage referring to resources such as the Corn, Soybean, Wheat, and Forages Field Guide developed by Extension specialists from The Ohio State University in partnership with Pennsylvania State University. No one knows everything, so it is helpful to rely on these scouting guides to make an accurate diagnosis in the field.

While scouting, it is also important to determine the population by counting the number of plants in a row length equal to 1,000th of an acre to inform replanting decisions. (View a video tutorial by Soybean and Small Grains State Specialist Dr. Laura Lindsey at https://go.osu.edu/standcount  for more details on taking a stand count.) Replanting, however, does not always guarantee a higher yield depending on the initial stand and planting date. For more information on making replanting decisions in corn and soybean, visit go.osu.edu/replant.

Seeds and seedlings are vulnerable to multiple stresses. It is important to scout fields following emergence to identify early-season issues and maximize yield and profitability this season. Make sure to subscribe to the Crop Observation and Recommendation Network Newsletter (C.O.R.N.), a product of the OSU Extension Agronomic Crops Team, for timely management guidelines. Take care and have a safe planting season.

Table 1. Symptoms and distribution of common soybean seedling blights and disorders. Source:  Crop Protection Network.