Severe Storms and Hail-Damaged Crops: Steps for Making the Right Decisions June 14, 2018
For more information on crop assessment and decision-making following hail, see the Hail Know section in CropWatch.
In recent weeks severe storms with hail left behind a wake of destruction in corn and soybean fields in parts of central and eastern Nebraska. This often causes frustration and anxiety for growers concerned about the fate of their crops and whether additional management or replanting is warranted. Before making any decision, talk with your crop insurance agent about your insurance coverage and options.
With any early-season hail damage, the most important first step is to give the crop time to regrow before assessing damage and making major decisions. The time lapse video included here shows how despite the appearance of devastating damage, corn may recover. Growth may be delayed as it recovers, but yields may be better than those from a field replanted in mid-June.
Half of all hail storms 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.
Yield loss assessments in corn are primarily based on live plant stand 7 to 10 days after a hail event. To assess a stand, evaluate at least four areas within the field. Each area should consist of 1/1,000th of an acre (or 17 feet 5 inches of row for 30-inch rows). Percent yield loss of hail-damaged corn fields can be estimated based on original and remaining plant stand data using tables from the USDA FCIC Corn Loss Adjustment Standards Handbook. Any decision to replant at this point in the season should take into account yield loss from the existing stand, potential yield if replanting this late, and other factors.
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 plant 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 may use wounds to infect plants. Cool, wet conditions after a hail event increase the likelihood of bacterial infections, but unfortunately, symptoms of these pathogen are unlikely to be apparent within 7 to 10 days of a hail event.
There are often questions about whether to use a foliar fungicide on corn following hail damage, as well. Foliar fungicide use in response to hail damage is not recommended because the pathogens that utilize the wounds created by hail, such as bacterial pathogens causing Goss’s bacterial wilt and blight, usually can not be managed with foliar fungicides. A few fungi may take advantage of wounds, such as common smut, a common fungal disease that creates mushroom-like galls on the plants, but most of these diseases can’t be controlled with fungicides either. Most of the limited research that has been conducted was primarily conducted later in the season (after tasseling), but showed no yield benefits of fungicide use for disease control. (See Effect of Foliar Fungicides on Corn with Simulated Hail Damage, Bradley and Ames, Plant Disease Journal, 2010.) Most fungi that cause plant diseases that can be managed with foliar fungicides have natural mechanisms for infection and don’t need or use wounds to infect plants.
Iowa State University colleagues weigh in on the topic: Would a fungicide benefit hail-damaged crops? in a recent Integrated Crop Management blog posting.
Unlike corn, the growing point of soybeans emerges as soon as the crop is visible. Delaying evaluation of plant stands for 7 to 10 days after a hail event is critical to determine whether 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 and may result in lodged plants later in the growing season.
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 1/1,000th 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 hail storm is to have patience. Emotions run high when hail decimates fields. It's best to wait 7 to 10 days following the storm to allow for plant recovery before assessing damage. (See Hail Know, Assess My Damage, for factors to consider when assessing damage early-season, in-season, and late-season.)
The risk of additional yield losses from bacterial plant pathogens increases under continuous corn. When possible, if replanting, rotate with other crops to reduce the potential for additional losses.
When deciding whether to replant corn or soybeans, consider:
- calendar date,
- yield potential of the replanted crop,
- weed situation,
- previously applied herbicides, residual periods, and label restrictions,
- seed availability,
- relative maturity/maturity group,
- crop value, and the
- cost of equipment and fuel.
Soybeans planted after hail typically will not require a seed treatment if soils have warmed above 60°F unless a significant disease problem is associated with the hail event and/or the field has a history of Phytophthora or Rhizoctonia.
Below are the yield potentials of corn and soybeans by planting date.
|Table 1. Relative yield potential of corn by planting date and population|
|Population||April 20–May 5||May 5–15||May 15–25||May 25-June 5||June 5–15|
|(Plants/Acre)||Percent Maximum Yield|