ILSOYADVISOR POST

Evaluate Late Emerging Soybeans

Disease Management
Dan Davidson
June 04, 2015

Most soybeans got planted in May and even during the last week of the month with remnants being planted in early June. Frequent rains really put a dampener on planting in a timely manner. With the majority of soybeans planted growers need to assess soybean stands to determine if their crop is doing well or needs to be replanted.

After soybeans emerge it’s time to do a little scouting to see how the stand looks, if emergence is even and if there are bare spots, and if emerged plants are showing signs of stress, discoloration or damage.

  • Determine the extent and severity of any problem. Is it throughout the field, or spotty and localized?
  • If emergence has just occurred, check carefully to be sure no more seed is sprouted and ready to emerge.
  • Take accurate stand counts.
  • Before replanting, identify the cause for the poor emergence and take steps to fix the situation.
  • If stand is uneven or there are skips down the row, dig to find the planted seed and its distribution.

First assess emergence and identify any bare spots. To determine the cause of uneven emergence, dig up seed in a bare an area to see if it germinated or if seed is healthy and free of disease or insect damage. If the seed is healthy and germinated but just not broken through the soil a rainfall will soften the soil surface. However, if you observe insects or disease damage take note because if the area is large enough you may have to replant it.

If seed hasn’t broken through the surface look for signs of crusting or water-ponding. When soil crusts over the hypocotyl won’t break through the soil surface and can eventually break off. Crusting is causes by fine clay soil particles settling on the soil surface after tillage and then baking over when it dries. If water ponds over and the soil saturates for an extended length of time, seedlings or roots will show necrotic lesions meaning they will be infected by fungi or water mold.

Look for early signs of discoloration or damage. When conditions are cool and moist soybeans may be yellow due to limited root activity or lack of nitrogen fixation. Other causes may be pH, nutrient deficiencies or herbicide damage. The following diagnostic table provides a list symptoms and possible cause.

Symptom

Possible Cause(s)

No seed

1. Improper planter adjustments worn parts, clogged spout, or empty box or tank, wrong plates, disks or drum, or excess or wrong seed treatment.
2. Digging and partly-eaten kernels by birds and/or rodents.

Normal seed appearance but not swelled

1. Cold or dry soil.
2. Poor seed-soil contact.

Normal seed appearance swelled but no sprout

1. Cold, dry, wet soil.
2. Phytotoxic pesticide or too much fertilizer close to the seed.
3. Needs more time for emergence to occur.

Seed dead, rotted

1. Seed rots, seedling blights, or fertilizer injury.
2. Dead seeds planted.
3. Cold, dry, wet or crusted soil.

Cotyledons fail to emerge

1. Crusted or cold soil.
2. Seed planted greater than 2" deep.
3. Injured seed during handling and planting.

Slow uneven emergence

1. Injured seed due to improper planter operation.
2. Seed planted too deep.
3. Unfavorable soil conditions.

Cotyledons and/or growing point damaged

1. Insect (bean leaf beetle, seedcorn maggot, or wireworms) injury.
2. Injury due to rodent, livestock, or wildlife feeding.

Seedlings pulled or dug up, seeds eaten

1. Bird or rodent damage.

Slow, uneven plant growth

1. Cold, dry, wet or compacted soil.
2. Herbicide carryover or stress.
3. Nematodes attacking roots.
4. Non-uniform planting depth.

Discolored leaves

1. Nutrient deficiency.
2. Water logged, cold, or compacted soil may cause nutrient deficiency.
3. Nematodes attacking roots.
4. Wind damage.
5. Frost or freeze damage.
6. High soil pH.

Leaves puckered, may be wilted

1. Drought.
2. Insects attacking roots or stem.
2. Nematodes attacking roots.
4. Chemical injury.

Shredded leaves or eaten plants

1. Wind or hail damage.
2. Insect feedings or livestock or wildlife grazing.

Leaves spotted, dead, or otherwise injured

1. Wind damage.
2. Nutrient deficiency.
3. Insect and/or disease issues.
4. Sunscald or cold.
5. Fertilizer or herbicide injury.

Plants wilt and die suddenly

1. Damage due to wind, lightning, or water logged soil.
2. Disease (fungal seedling blights).
3. Herbicide injury.

Inhibited root development or malformed roots

1. Nematode activity.
2. Root rot diseases, insect feedings, or herbicide injury.

Hypocotyl thickened with limited, stubby roots

1. Herbicide injury.
2. Soil compaction.
3. Disease — water soaked lesion (Pythium or Phytophthora) or dry lesion (Rhizoctonia or Fusarium).

Adapted from http://www.aganytime.com/asgrow/mgt/growing-season/Pages/Stages.aspx.

Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com.

Dan Davidson
Soybean agronomist Daniel Davidson, Ph.D., posts blogs on topics related to soybean agronomy. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.


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