All crop producers agree that assessing hail damage is a very emotional experience. Damage to soybean plants should be assessed a few days after the event to minimize rash decisions to replant, allow time to assess potential crop recovery, and schedule a field visit with your insurance agent. However, it is appropriate to scout fields immediate after a hail event to generate a list of fields to revisit in a few days. So how do you assess hail damage and should you replant?
Above: Picture of hail-damaged soybeans in Day County taken on June 16.
Photo Credit: Ryan Wagner
Assessing Hail Damage
The growing point(s) or bud(s) are above the ground in soybean, unlike corn early in the season. For this reason, assessing aboveground growth in soybean is all that is need to assess potential recovery. New buds should appear in about three to five days. The primary goal in the assessment is to determine the number of plants with new buds that can recover per acre.
The terminal growing point or bud (apical meristem) is a region of actively dividing cells located at the tip of the main stem. The terminal bud along with the axillary buds located in the axil between the main stem and each leaf stem all have the potential for regrowth if they are intact. The two cotyledons, the two unifoliolate leaves, and all the trifoliolate leaves have an axillary bud.
If the seedling was at the V1 stage (one trifoliolate leaf), the seedling would have a terminal bud plus axillary buds at the cotyledons, unifoliolate leaves, and the one trifoliolate leaf for a total of one terminal bud; and five axillary buds for a grand total of six buds available for regrowth. Growing points are critical because they create all of the plant’s leaves, buds and stems, and terminates in the uppermost trifoliolate leaf and its associated buds and pods. Therefore, if there is no terminal or any axillary buds, the plant has no means of recovering. Only one bud (terminal or axillary) is needed for regrowth and recovery. Hail damage can occur almost anytime during the growing season. However, hail damage in May and June needs to be critically evaluated to determine if replanting is an economically viable option. Hail causes defoliation and stem bruising/breakage. The amount of yield loss is dependent on growth stage, amount of damage, and surviving plant population. In many cases, the leaves may be stripped from the plant and recovery is possible if buds exist. Plants cut off below the cotyledons have no means of regrowth. If damaged plants are completely defoliated but have a stem, you still must look for axillary buds. Look for scars where the leaf stems were attached before the hail. If you can find the scars where the cotyledons were attached, you should find an axillary bud immediately above each of the two scars where the cotyledons were attached. If they are present, the plant has the potential to recover.
In most situations soybeans have a large capacity to compensate for thin and uneven stands, especially when hail damage occurs during the vegetative growth stages in May and June. Random loss of soybean plants across a field from hail damage is less worrisome if more than 75,000 live plants per acre still exist. Research in Minnesota showed no yield decrease even if one-foot gaps existed in the row with a soybean stand of 75,000 plants per acre compared to a full stand (150,000 plants/acre) prior to the V4 growth stage (Hicks et al., 1990). Hick et al. (1990) found that even two-foot gaps in the row with a stand of 75,000 plants per acres decreased yield by only four bushels/acre prior to the V4 growth stage. Unfortunately the decision to replant a soybean field is not always very clear and is dependent on both the size and extent of damage.
Things to consider before replanting:
- If the average surviving soybean plant population is 75,000 or more after June 10, leave it alone even if one-foot gaps exist in the row.
- Yields decreases are ½ bushel per acre per day or more after June 14 in South Dakota with later plantings.
Things to consider if replanting:
- Reduce the maturity group of the soybean planted by 0.5 in mid-June to as much as 1.0 by early-July compared to a full-season variety adapted to your area.
- Use narrow rows and increasing seeding rates when seeding late in the season.
- Hicks, D.R., W.E. Lueschen, and J.H. Ford. 1990. Effect of stand density and thinning on soybean. Journal of Production Agriculture 3:587-590.