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Hail Damage on Soybeans and Corn

Intense weather has resulted in hail damage in a few regions in Southwestern Ontario. Although most areas received only minimal damage a few fields did suffer significant injury. See figures #1 and #2.

Figure 1. Hail damage in soybeans - Monday, June 24th near Tavistock, Ontario

Figure 2. Hail damage in corn - Monday, June 24th near Tavistock, Ontario

Soybeans

The full extent of early season hail damage is difficult to assess immediately after a storm. Plants can often recover as long as the stem is in tack up to where the cotyledons were attached. It generally takes at least 4 to 7 days before a good assessment of a field can be made unless the damage is extreme. If 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. Those plants damaged below the cotyledons by early-season hail will not recover. It's important to give the plant the chance to develop new growth before making a decision on the field. This could take up to 7 days. Research trials show that leaf loss at early growth stages has little impact on final yield or maturity. Table 1, Percent Yield Loss of Indeterminate Soybean at Various Levels of Leaf Area Loss and Growth Stages.

Soybean 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.

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.

Corn

Yield loss due to hail is dependent on the stage of the crop at the time of the hail event and the level of defoliation. Yield loss is greatest when the corn is defoliated during tasselling. Younger plants may experience a delay in growth and development due to hail, but yield loss is usually minimal. Defoliation of plants near maturity tends to cause little yield loss. Refer to Table #2 Estimated Percentage of Corn Grain Yield Loss Due to Defoliation at Various Growth Stages, when making yield loss estimates due to hail damage. Hail damage may also provide an entry point for diseases such as smut.

Foliar Fungicides

When plants are damaged they become more susceptible to disease. It has been suggested that a foliar fungicide application may increase yields when plants have been damaged by hail. Little data is available to date since foliar fungicide on these crops are relatively new to Ontario. A few on farm strip trials will be undertaken this year to assess the potential of foliar fungicides in these cases.

Source: National Crop Insurance Services Inc. 1997.

¹Adapted from the National Crop Insurance Services Corn Loss Instruction (Rev. 1984). Used with permission.
²As determined by counting leaves using the leaf over method (i.e., those with 40% - 50% of leaf exposed from whorl and whose tip points below the horizontal).