Early detection and diagnosis of soybean emergence problems

Detecting soybean emergence problems early and correctly identifying the reasons for the failures is essential for making replant decisions.

Early detection and diagnosis of soybean emergence problems is important to achieving high yields. Determining the reasons for poor emergence 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 18 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 seeds or seedlings and inspect them for signs of disease or insect damage to the root, hypocotyl (stem of the germinating seedling) or cotyledons (seed leaves).

In most fields, the major insect pests affecting seedling emergence are seed corn maggots, white grubs and wireworms. Seed corn maggot adults lay their eggs in fields where manure, cover crops or weeds have been incorporated into the soil within the past two weeks. 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 (Acceleron IX 409 or Gaucho, for example) or thiamethoxam (Cruiser) 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 thiamethoxam prior to replanting.

Phytophthora, Pythium, Rhizoctonia and Fusarium are soilborne fungi that are most likely to cause seed rots or seedling blights in soybeans. Fusarium species are present over a wide range of temperatures and differ in their virulence to soybeans. They may not kill seed outright, but may cause stunting and root rots later on. Pythium is more likely to create problems in soybeans that are planted early because it prefers cool soil conditions. Where Pythium is prevalent in soils, infection is likely when soil temperatures are cool and a heavy rain occurs within 24 hours after planting. Infected seeds have swollen and bent hypocotyls; infected plants have rotted roots and pull easily from the soil. Replanting with seed treated with a fungicide containing mefanoxam or metalaxyl, or waiting until the soil temperature exceeds 60°F, should result in satisfactory emergence. Phytophthora is favored by poorly drained or saturated soils and warmer temperatures of 68 to 77°F. If seedlings emerged from the soil but died quickly, Phytophthora is a likely suspect. Replant with varieties having specific race resistance or seed treated with mefanoxam at 0.64 fl oz/per cwt. Warmer temperatures of 75 to 89°F and drier conditions are conducive to Rhizoctonia. Reddish-brown or brown lesions on the stem cortex that are firm and dry are characteristic of Rhizoctonia infection.

If no insect feeding or disease symptoms and 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 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 enables the emerging seedlings to crack the crust.

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. Funding for the SMaRT project is provided by MSU Extension and the Michigan Soybean Checkoff program.

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