You likely won’t need Sherlock Holmes or Columbo to figure out why your soybean stands aren’t up to par. You just need a pair of comfortable shoes, a pocketknife, a shovel and the Purdue University Corn & Soybean Field Guide.
Steve Gauck, a regional agronomy manager for Beck’s, Greensburg, Ind., says assessing stands is one of the most important scouting activities early in the season. “If stands are reduced, you need to go deeper than just calculating if there are enough plants remaining or whether you need to replant,” Gauck says. “You should scour for the ‘why?’ Why are your stands reduced?
“If you can determine why, you can make planter adjustments or change strategies about planting when soils aren’t right or maybe adjust your seed treatments for next season, even if you leave this year’s stand. If you don’t scout early and figure out what happened to plants that are missing, you could be destined to facing the same dilemma next year.”
There are seven potential answers to the “why plants are missing” question, Gauck says. Keep these seven potential factors in mind:
1. Soil crusting. Call it surface soil compaction if you like. Whatever you call it, if soils are hard enough that soybeans “break their necks” trying to emerge through the crust, it will reduce stands. The hypocotyl must be able to pull the cotyledons, the original seed halves, above ground without breaking them off.
2. Open seed trench. If the seed trench doesn’t close properly, often because the soil was too wet for proper planting, several things can happen, and they’re all bad. Insects or rodents have open access to seed. Seed can dry out if it doesn’t rain soon enough, and the seed may lay in the open trench without germinating.
3. Slugs feeding on seeds and plants. If the seed slot is left open, it’s an open invitation for slugs. Even if it’s closed and soybeans emerge but slugs are present, which can happen in a cool, wet spring, especially in higher residue situations, slugs can destroy young seedlings.
4. Insect damage to stem, roots and cotyledons. There are insects such as seed corn maggots that can also attack soybean seeds and create empty spots where there should be plants. According to the Purdue guide, white grubs can prune roots and cause small plants to wilt and die. Wireworms, often thought to be more of an issue for corn, can also attack soybean seeds and seedlings, killing plants. Once wireworms are in a field, they can return to the same spots for several seasons.
5. Diseases. Seedling diseases can occur at high enough levels to kill seedlings, especially in cool, wet conditions. Sometimes symptoms of disease and injury from preemergence herbicides can be confused. Either one can result in missing plants. If you don’t visit and diagnose it while it’s occurring, you may blame the wrong culprit.
6. Planting depth. You can plant too deep, but the condition related to planting depth most likely to cause missing plants is planting too shallow, Gauck says. There may not be enough moisture for seeds to complete emergence.
7. Poor germination. Check the seed tag. You won’t find 100%. Some seeds just won’t germinate. If you’re scouting early, you should find these seeds.