MSU Extension

Early detection and diagnosis of soybean emergence problems is important to achieving high yields. Early detection and diagnosis enables you to minimize yield losses by taking prompt corrective action such as rotary hoeing or replanting if necessary. Soybean emergence ranges from six days under ideal conditions to 15 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 cotyledons.

Seed corn maggot is the insect pest most likely to affect soybean seedling emergence in Michigan. However, white grubs and wireworms may be present in high numbers when planting soybeans into a grass sod. Seed corn maggot adults lay their eggs in fields where manure or green plant material has been incorporated into the soil within two weeks of planting.

If seed corn 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 not be attractive two weeks after incorporation. Seed treatments containing imidacloprid, clothianidin and thiamethoxam will provide additional protection from seed corn maggots. If wireworms or white grubs are responsible for the stand reduction, the seed will need to be treated with clothianidin or thiamethoxam prior to replanting.

Phytophthora, Pythium, Rhizoctonia and Fusarium are the soil-borne diseases most likely to damage germinating soybean seed. Fusarium species 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 Michigan soils and damage is likely when soil temperatures are cool and a heavy rain occurs within 24 hours after planting. Affected plants will have swollen and bent hypocotyls. Replanting when the soil temperature exceeds 60 degrees Fahrenheit should result in satisfactory emergence. Warmer temperatures of 75-89 F and drier conditions are conducive to Rhizoctonia.

Phytophthora is favored by poorly drained soils and warmer temperatures of 68-77 F. If seedlings emerged from the soil but died quickly, Phytophthora is a likely suspect. Replant with varieties having specific race resistance or plant varieties having a high level of field tolerance plus a seed treatment effective on Phytophthora.

If no insect feeding or disease symptoms or lesions are present, determine if the surface of the soil has developed a crust. If a crust exists and significant rainfall greater than 0.5 inches is not predicted, 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 the larger cotyledons. Soybeans planted in 30-inch rows are more likely to emerge from crusted soils than beans planted in narrow rows as the closer seed spacing within the row enables the emerging seedlings to crack the crust. Seedlings that have lost only one cotyledon when emerging from crusted soils will produce normal yields. When both cotyledons are pulled off during emergence, yield losses will range between 2 and 7 percent.

If insects, diseases and crusting are not the problem, determine if the planting depth is correct (1 to 1.5 inches deep) 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 serious planting problems are found and the stand is not adequate, the field may need to be replanted.

If no planting problems are detected and the seeds or seedlings look healthy, inadequate soil moisture is the likely 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. Also consider the following information when making replant decisions:

• Yield losses of 0.4 of a bushel per acre per day have been shown to occur when planting is delayed after mid-May.
• Uniform stands of 100,000 plants per acre in narrow rows and 80,000 plants per acre in 30-inch rows have the potential to produce good yields.
• Seed for high-yielding varieties may not be available for replanting.

This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. SMaRT is a partnership between Michigan State University Extension and the Michigan Soybean Checkoff program.