Soybeans: Other Problems

Excerpt from Agronomy Guide for Field Crops (Chapter 4)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Frost and Hail Damage
   • Early Season
     • Percent Yield Loss of Indeterminate Soybean at Various Levels of Leaf Area Loss and Growth Stages - Table 4-24
   • Stem Damage
2. Late Season Cold Temperature and Frost Injury
   • Soybean Response to Freeze Damage - Table 4-25
3. Updates on Soybeans: Other Problems
4. Related links...

Frost and Hail Damage

Early Season

Plants damaged below the cotyledons by early-season frost or hail will not recover. If frost or hail damages the growing point of the seedling, but not the stem portion below, the plant will send out new shoots from the base of the leaves or cotyledons.

Plate 78. Frost injury. If frost damages the growing point, but not the stem, the plant may recover by new growth emerging at the leaf axils.

Wait 3 or 4 days and watch for new growth to emerge from the point where leaves attach to the stem (leaf axils). Research trials show that leaf loss at early growth stages has little impact on final yield or maturity. Table 4-24, Percent Yield Loss of Indeterminate Soybean at Various Levels of Leaf Area Loss and Growth Stages, summarizes the expected yield loss from leaf loss at various life stages.

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Source: National Crop Insurance Services Inc., 1997.

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Stem Damage

Broken or cut-off stems have greater impact than leaf loss on yield and maturity. If stem loss is under 50% prior to flowering, yield loss will be less than 10%. When evaluating hail damage, check for bruising on the plant stem. Severe damage to the stem will make it more difficult for the plant to recover. It can also make the plant more susceptible to disease. Bruising, which does not cause stem breakage, causes minimal loss in yield.

Plate 79. Hail damage. Soybeans are most vulnerable to hail damage during flowering and pod fill.

In terms of yield reduction, soybeans are most vulnerable during the flowering and seed fill period. This is particularly true if stems are broken, resulting in a reduction in the number of pods. Delays in maturity and seed size also occur.

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Late Season Cold Temperature and Frost Injury

Soybeans are regarded as a warm-season crop and are therefore more susceptible to cold temperatures, especially during flowering. It is believed that sustained cold temperatures (less than 13°C or 55°F) during flowering affect proper formation of pollen in the flower. This results in poorly developed pods called parthencarpic pods (also called "monkey pods"). There is some variety difference in tolerance to cold temperatures as was experienced in 1992.

Varieties that have tawny pubescence (i.e., yellowish-brown hair) are more cold tolerant than those that have grey pubescence.

Frost during flowering and pod fill can drastically reduce yield and quality (see Table 4-25, Soybean Response to Freeze Damage).

Source: Saliba et. at. Kansas State University, 1982

Freezing during pod fill will result in severely damaged beans with a greenish, "candied" appearance. Even moderately frosted beans with a greenish colour and slightly wrinkled seed coat are considered damaged and can be discounted if present in excess of limits. The seed will eventually dry down with a wrinkled seed coat. Frost-injured plants may reach maturity earlier but will have seed moisture equal to non-frosted plants. Germination will also be severely reduced. The Canadian Food Inspection Agency classifies frost-damaged soybeans as those "soybeans whose cotyledons, when cut, are green or greenish-brown in colour with a glassy, wax-like appearance."

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Updates on Soybeans: Other Problems

No updates available at this time.

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Related links...

• Soybeans

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