Soybean Pest Beat: If you didn’t use a fungicide or insecticide, evaluate seed quality closely at harvest.
Aug 04, 2020
I don’t spray fungicides or insecticides. Are there clues I should be looking for in seed quality at harvest that will let me know if I had disease or insect issues in my soybeans?
The Indiana certified crop advisers panel answering this question includes Steve Gauck, regional agronomy manager for Beck’s, Greensburg; Andy Like, independent crops consultant, Vincennes; and Dan Ritter, agronomist with Corteva Agriscience, Rensselaer.
Gauck: Scouting and determining issues before harvest will help you develop a plan and learn what issues are affecting your crops and yield. Weather and harvest timing have a large impact on seed quality at the end of the year.
Mainly, people think of fungicides as a plant health product, but some don’t always realize the effect it can have on seed. Creating a healthy plant promotes larger seed size and a longer grain fill period. If you discourage disease in the plant, you don’t allow certain diseases to affect seeds.
As for insects, scout and look for feeding on soybean pods. This feeding allows an avenue for disease to enter the seed. The seeds inside the pod can have feeding damage on them, as well as mold from where moisture entered the pod after insects opened the door.
Scouting before harvest helps you know if insects or disease caused a seed quality issue and allows you to develop a plan for next year to improve seed quality.
Like: Yes, looking at seed quality can give you an idea of what insects and diseases you had during the growing season. Small, discolored and malformed seeds generally point to stinkbug damage. Purple staining on the seed would indicate Cercospora leaf blight. Pod and stem blight can be characterized by small, moldy seeds that are typically harvested late. It’s most common where fields haven’t been rotated out of soybeans for a while.
Keep in mind, the best way to know what disease and insects you have is by scouting during the growing season. By doing so, you may also have a chance to apply an insecticide or fungicide to prevent damage and yield loss during the season.
Ritter: When it comes to seed quality, look for off-colored or damaged soybeans. Diseases that may leave clues in the seed are Cercospora, also known as purple seed stain; Sclerotinia, or white mold, which leaves behind sclerotia that look like rat droppings; Phomopsis; and soybean pod mottle virus. Check out the publication by the Crop Protection Network. It’s a useful resource I use for this information in greater detail, with excellent photographs on what some of the problems look like.
Check for damaged soybeans showing evidence of feeding by stinkbugs, bean leaf beetles and grasshoppers. These tend to be the most common pod-feeding insects that may damage the soybean seed. This feeding can also encourage rots and molds to infect the seed. So be on the lookout for those issues in addition to physical feeding injury, which would be obvious on the seed.