Justin McMechan demonstrates Nebraska Extension's new hail machine
PUT ON ICE: Crop specialist Justin McMechan demonstrates Nebraska Extension's new hail machine at an open house last year.

Evaluating early-season hail damage in corn, soybeans

Extension Crop Connection: Yield loss from hail damage depends on timing, severity and subsequent weather.

By Justin McMechan

Temperatures have been gradually increasing over the past few weeks, signaling the start to another growing season. Unfortunately, these same systems were accompanied by some severe storms, reminding us of the early-season threats, such as hail, to our cropping systems.

For many of us, the sight of a hail-damaged field raises emotions and a call for immediate action; however, it is critical to allow the crop time to respond for a proper evaluation of yield losses.

Yield losses from hail damage in corn and soybeans will depend on the timing and severity of the hail event, as well as the environmental conditions that follow. Regardless of the level of damage, farmers should be patient when evaluating early-season hail damage and wait seven to 10 days after a hail event to allow for crop regrowth.

Corn
Half of all hailstorms occur during the early stages of corn growth when replanting is still a viable option. Prior to V6, the growing point of corn remains below the soil surface. As a result, the removal or damage of plant tissue during this period is estimated to have little impact on plant yield. Therefore, yield loss assessments in corn are primarily based on live plant stand seven to 10 days after a hail event.

To evaluate stands, farmers should check at least four different areas in a field. Each area should consist of a 1,000th of an acre (or 17.5 feet of row for 30-inch rows). Percent yield loss of hail-damaged cornfields can be estimated based on original and remaining plant stand data using tables from the USDA FCIC Corn Loss Adjustment Standards Handbook.

Plants with abnormal growth (wrapped or tied) should be considered as "non-living" during this evaluation because their ability to recover is uncertain. (Note: Under certain situations, a crop adjustor may delay early-season hail evaluations when a high percentage of plants exhibit abnormal growth from hail damage.)

In some cases, farmers may be tempted to clip these plants to allow for normal growth. However, previous research has found highly variable yields with clipped compared to unclipped plants. We also strongly advise farmers not to clip abnormal plants, as this may spread plant diseases across the field.

Bacterial plant pathogens such as Goss's wilt are of greater concern than fungal pathogens following a hail event. Unlike fungal plant pathogens, bacterial pathogens often need wounds to get into plant. Cool, wet conditions after a hail event increase the likelihood of bacterial infections. Symptoms of these pathogens are unlikely to be apparent within seven to 10 days of a hail event.

Soybeans
Unlike corn, the growing point of soybeans emerges as soon as the crop is visible. Delaying evaluation of plant stands for seven to 10 days after a hail event is critical to determine if a viable growing point is still present. Physical presence of nodes does not imply that a plant is still alive. Stem damage below the growing point can result in an inability to move nutrients and water to the rest of the plant.

Early-season evaluations are based on two components: remaining plants per acre and percentage of nodes that are cut off or broken. Plants stands are evaluated in a similar method to corn on a 1,000th of an area in at least four different areas of a field.

Cut or broken nodes are also accounted for as a percentage of the total number of nodes compared to an undamaged plant. Yield loss estimates from stand loss and cut or broken nodes can be estimated using tables from the USDA FCIC Soybean Loss Adjustment Standards Handbook.

The best advice following a hailstorm is to have patience. Emotions run high when hail decimates fields, and it's best to wait seven to 10 days following the storm to assess damage and allow for plant recovery.

The risk of additional yield losses from bacterial plant pathogens increases under continuous corn. When possible, rotate with other crops to reduce the potential for additional losses. When replanting corn or soybeans, farmers should also consider calendar date, weed situation, seed availability, relative maturity and maturity group, crop value, and the cost of equipment and fuel.

McMechan is a Nebraska Extension assistant professor and cropping systems specialist.

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