Soybean Troubleshooting

Last updated on February 23, 2014

Soybean Growth Problems

General categories

Poor emergence or reduced plant population

  • soil crusting
  • insect damage
  • disease
  • dry soils
  • soils saturated with water for several days
  • salt injury from fertilizer
  • herbicide damage
  • planting too deep

Chlorosis: yellowing of plants across the entire leaf surface or between the veins

  • potassium deficiency
  • zinc deficiency
  • manganese deficiency
  • iron deficiency
  • herbicide injury
  • diseases
  • insects

Necrosis: spots or streaks of dead tissue

  • fertilizer spray injury
  • herbicide injury
  • disease
  • wind damage
  • hail damage
  • insects

Puckered or cupped leaves

  • acid soils (manganese toxicity)
  • boron toxicity
  • herbicide drift
  • biuret
  • potato leafhopper
  • environmental conditions

Holes in leaf and stalk tissue, or plant tissue consumed

  • insect feeding
  • hail or wind damage

Injury to pods

  • insects
  • diseases

Weather related problems

  • Soil crusting
  • Frost
  • Water damage
  • Hail
  • Lighting

Herbicide Injury Symptoms

Diseases

Nutrient Deficiency and Toxicity Symptoms

Insect Injury

Unless the soybean crop is totally gone following hail, the first thing to do is to wait three days. By that time, if temperatures favor soybean growth, regrowth should be evident. Regrowth will come from meristem regions of the plant, in the axil areas where the leaf sttaches to the stem.

If soybeans are cut off below the cotyledons, they aren't coming back - for there are no meristems from where regrowth can originate.

If cotyledons are removed by hail from newly emerged soybeans (but the stem below coytledon node is not cut), regrowth may or may not occur. Wait three days and watch meristems, both along the stem where cotyledons and / or leaves are attached.

If leaf tissue is reduced on soybean seedlings, a rather high percentage of total leaf surface can be removed without reducing yield potential. If half of the leaf tissue is still present on soybean seedlings, they will likely show no reduction in yield at the end of the summer. Leaf removal guidelines used by entomology for insect feeding are essentially the same as leaf removal damage tables used by hail insurance agents.

If plants are cut off - reducing total number of living plants/acre, and remaining plants are reasonably distributed in the row, a stand density of 75,000 to 100,000/acre is likely to be better than replanting. I believe the hail insurance industry will pay a little for lost potential if stands drop below 120,000, but it is only a percent or two.

Soybean Yield Loss Due To Hail Damage
Hail can cause huge yield losses to soybean fields. But as a grower it is in your best interest to be able to evaluate your field after a hail storm and decide if the field indeed needs to be replanted. Every little bit counts in terms of your bottom line and unnecessarily replanting soybean fields is a waste of time and money. This information is intended for a guideline only. Whenever in doubt it is always best to consult an Agronomist or Hail Adjuster before replanting.

First of all, remember that it is best to evaluate hail damage 7-10 days after the damage occurred. This is hard to do when you want to get back into the field and replant as soon as possible. This will allow you to see any regrowth that is occurring.

Partsofplant.gif (24576 bytes) To be able to inspect soybean plants properly it is important to know the parts of a soybean plant.

Starting at the bottom of the plant are the Lateral roots, these intercept nutrients and take up water.

The stem or Hypocotyl translocates water and nutrients to the rest of the plant.

The Cotyledons hold stored nutrients for the plant in its early stages.

Above the Cotyledons are the Axillary buds and the Unifoliate leaves. The plant will grow new branches from the Axillary buds.

The Growing point is where the main stem of the plant grows and produces new tissue.

Finally, the Trifoliate leaves intercept sunlight for photosynthesis which produces energy for the plant.

When checking the plants for damage it is important to carefully inspect each plant to see what kind of damage was inflicted by the hail. A plant cut off below the cotyledons will not recover. Both cotyledons can be knocked off of the plant if the growing point remains intact. Use the table below to help you decide which plants will live and which ones will not.

Condition Will the plant survive?
Plant cut off below the cotyledons No
Plant missing one cotyledon Yes
Plant missing both cotyledons but growing point intact Yes
Plant cut off above unifoliolate leaves Yes
Plant with no remaining leaf tissue and shows no regrowth No
Plant lightly bruised on the stem Yes
Plant severely bruised and folds over No
After 7-10 days plant shows regrowth form axillary bud Yes

Using these guidelines its time to head to the field. Bring a tape measure along and measure out 10' of row. Start by checking each plant and count the ones that are going to survive. You can lose up to half of the stand without losing much yield. If you are in 30" rows and have a surviving stand of 5 plants per foot you may not want to replant.

One other thing to remember is that you need to take into account the amount of leaf area that was damaged. Plants that are damaged before flowering are not significantly effected by loss of leaf area. If the plants are flowering and some leaf area is damaged or missing you need to take that into account when figuring yield loss.

Percent held loss of indeterminate soybean varieties as affected by degree of defoliation.
  Growth Defoliation (% leaf area destroyed)
Stage 10 20 30 40 50 60 70 80 90 100
R1-2 0 2 3 5 6 7 9 12 16 23
R3 2 3 4 6 8 11 14 18 24 33
R4 3 5 7 9 12 16 22 30 39 56
R5 4 7 10 13 17 23 31 43 58 75
R6 1 6 9 11 14 18 23 31 41 53
Data from University of Nebraska NebGuide G85-762

Soybeans usually flower around the first week in July so you probably won't use this chart in deciding to replant but it gives you an idea of yield loss from hail later in the season.

Use the Planting Rate Recommendation Chart to figure your surviving population. Find the row spacing that you use and go down to "Feet Of Row/Acre". Multiply your surviving stand (plants/foot) by the Feet Of Row/Acre number.

Sample for 30" rows. 5 plants/foot X 17,428 feet of row/acre = 87,120 plants/acre

You have 87,120 plants/acre, how does that effect yield?

Effect Of Population Reduction On Yield
Plants/Acre Percent of optimum Percent yield produced
157,000 100% 100%
118,000 75% 98%
78,000 50% 90%
39,000 25% 75%
Data from Minnesota Extension Field Book  

Now its time to check the calendar. If it is June 4 and you only have 40,000 plants/acre, its time to replant. If it is June 9 or later, you might not want to plant. Refer to the table below. Even though 40,000 plants/acre is a thin stand, you could end up with 75% of normal yield. If you replant on June 9 you also might get 75% of normal yield. However, you would also have extra costs involved.

Planting Date Effect On Soybean Yield
Planting Date Yield (%)
May 1   100
  5   98
  10   97
  15   96
  20   92
  25   89
  30   85
June 4   80
  9   75
  14   69

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