Soybean Corner: Growth stage, amount of defoliation and date all factor into replant decisions.
May 27, 2020
If my soybean fields are hit by hail in early July, should I consider replanting?
The Indiana certified crop advisers panel answering this question includes Betsy Bower, agronomist, Ceres Solutions, Terre Haute; Jesse Grogan, regional manager, AgReliant Genetics LLC, Lafayette; and Stan Miles, agronomist, A&L Great Lakes Labs, Fort Wayne.
Bower: First, assess how badly hail hurt soybeans. It will likely take three to six days to get a good picture.
Iowa State University has a pretty good Extension publication, Hail Damage Assessment to Soybeans. Iowa State suggests digging up plants in at least 3 feet of row and separating them into three piles: live plants, questionable plants and dead plants. Repeat this several times. Add live plants to half the number of questionable plants and divide by length of row to get live plants per foot of row.
Look for new axillary bud growth at the base of each trifoliate. In early July, you would likely have at least three to more than seven or eight potential axillary buds for new trifoliates to initiate.
Also look for bruising, both shallow and deep, along the stem. Deep bruising below new growth may lead to lodging later.
In southern Indiana, double-crop beans are the norm, but early July is still getting a little late. Increase planting populations and consider early-maturing varieties if you replant.
Grogan: Soybeans recover beyond expectations from hail damage in midsummer when stand loss isn’t greatly reduced. Soybeans are most sensitive to hail in the newly emerged and early seedling stages. Soybean plants are in the V4 to R1 stage in early July. Damaged plants develop new leaves from existing axillary buds at the stem nodes. Wait at least three to four days to evaluate regrowth before deciding on action.
Yield recovery from hail can be 80% to 90%, depending on how much leaf tissue is destroyed, when plant stands are at or above 100,000 plants per acre. Leaf loss of 30% to 60% results in good recovery compared to 100% leaf loss. Researchers at the University of Minnesota reported leaf loss of 66% resulted in a yield loss of 6%.
Yield loss is increased with a 50% stand reduction to a 21% loss at R1. Plants at R3 are more sensitive to loss than plants at R1. A 100% leaf loss at R3 would result in a 69% yield loss. Replanting should only be considered if there is huge leaf and stand loss at R1 and especially at R3.
Allowing a stand to recover is a good option when only 33% to 66% leaf loss occurs. Maintain good weed control.
Miles: The most critical growth stage for soybean plant damage is about R5. According to the University of Nebraska, up to 75% of potential yield may be lost from an event that causes complete defoliation. However, unlike corn, soybeans have multiple growing points that may allow the crop to regenerate leaves and recover up to 70% of its yield potential in optimum conditions.
When considering replanting in July, it’s necessary to perform a breakeven analysis on the yield potential of the late-planted crop and determine the economic “line in the sand” date. In many scenarios, a reduced yield potential will exceed net income of a very late replanted crop.
If the damaged crop is left, additional scouting and crop inputs may be needed to manage increased weed and disease pressure.