Diagnosing soybean emergence problems
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Early detection and diagnosis of soybean emergence problems is always important to achieving high yields. However, early season-scouting is even more important this year due to a reduction in seed quality. Soybean emergence ranges from six days under ideal conditions to 14 days under more challenging soil conditions. Conditions that can lead to delayed or uneven emergence include: cold soil temperatures, excess soil moisture, inadequate soil moisture, soil crusting, improper seeding depth or uniformity, poor seed-to-soil contact, insect feeding and disease infestations. If slow or uneven emergence occurs, dig up the plants and inspect them for signs of disease or insect damage to the root, hypocotyl or cotelydons.
In most fields, the major insect pests affecting seedling emergence are seedcorn maggots, white grubs and wireworms. If seedcorn maggots have reduced the stand to an unacceptable level, replanting should correct the problem as the decaying organic material that lured the adults to the field should no longer be as attractive. If wireworms or white grubs are responsible for unacceptable stands, the seed will need to be treated with Cruiser prior to replanting.
Phytophthora, Pythium, Rhizoctonia and Fusarium are the soil-borne diseases most likely to damage germinating soybean seed. Fusarium spp. are present over a wide range of temperatures and may not kill seed outright, but may cause stunting and root rots later on. Pythium is more likely to create problems under cool, wet soil conditions. Pythium is prevalent in southwest Michigan soils and damage is likely to occur when a heavy rain occurs within 24 hours of planting. Affected plants will have swollen and bent hypocotyls. Replanting when the soil temperatures exceed 60ºF should result in satisfactory emergence. Warmer temperatures and drier conditions favor Rhizoctonia (75-89°F). Phytophthora is favored by poorly drained soils and warmer temperatures (68-77°F). If seedlings emerged from the soil but died quickly, Phytophthora is a likely suspect. Replant with resistant varieties or fungicide-treated seed.
If no insect feeding or disease symptoms/lesions are present, determine if the surface of the soil has developed a crust. If a crust exists, consider using a rotary hoe to break up the crust. To prevent damage to emerging seedlings, avoid rotary hoeing when the plants are in the “crook” stage and for three days after this brittle stage occurs. Large soybean seed is more likely to experience emergence problems in crusted soils than small soybean seed due to their larger cotelydons. If crusting is not the problem, determine if the planting depth is correct and uniform and check to see that soil is firmed around the seeds. Some varieties may not emerge well when planted at depths of 2 inches or more. If no planting problems are detected, and the seeds/seedlings look healthy, inadequate soil moisture is likely the cause of the delayed emergence. Wait until a rain occurs and recheck the field.
When deciding if replanting is warranted, always compare the yield potential of the existing stand to that of the replanted stand and account for all replanting costs. Consider the following information: yield losses of 0.6 of a bushel per acre per day have been shown to occur when planting is delayed after mid-May, a uniform stand of 100,000 plants per acre will produce good yields and seed supplies are short this year, so seed from high-yielding varieties may not be available.