Extension educators advise on assessing hail-damaged corn, beans
ST. PAUL -- Recent storms damaged crops in an area from Lyon through Renville counties. Corn in this area had seven to eight leaf collars when damaged, and soybean had three to five fully developed trifoliolate leaves.
According to University of Minnesota Extension agronomist Jeff Coulter, corn survival can be determined by splitting stalks and examining the growing point. At the seven-leaf collar stage, the growing point is located about 1-2 inches above the soil surface and looks like an arrowhead. Healthy growing points will be firm and white to yellow in color. If damaged, the growing point will be watery and orange to brown in color, and the plant will not survive. Corn plants with damaged whorls generally regrow, but sometimes the leaves become tightly bound in the whorl and have difficulty growing out. "Plants exhibiting severe leaf binding are not likely to contribute much to yield," Coulter said.
Extension agronomist Seth Naeve says that soybean plants with significant amounts of green tissue remaining (more than one green cotyledon and/or remaining leaf tissue) are likely to survive early season hail damage, as they can regrow from axillary buds located at the juncture of the stem and leaves. Soybean plants cut below the cotyledons will not recover.
"Soybean can tolerate low populations very well, with only small reductions in yield potential across wide ranges in plant loss," said Naeve. For instance, populations near 100,000 plants per acre are likely to produce maximum yields, and those around 80,000 will yield about 90 percent of the maximum. However, expected yields drop more rapidly in stands below 50,000, with 39,000 plants per acre likely to produce about 75 percent of the normal yield.
For corn, 28,000 plants per acre will yield about 95 percent of the maximum, while a final stand of 16,000 plants per acre will yield about 76 percent of the maximum. Corn yield loss also depends on leaf loss, with 80 percent leaf loss at the seven to eight leaf collar stage reducing yield by about 10 percent. In soybean, leaf loss up through the time the plant has four fully developed trifoliolate leaves has little effect on yield.
Replanting should be considered only in fields where the crop is a total loss. Replanting corn at this time is not an option as the crop will not mature in time to make grain or silage. Soybeans may be replanted, but yields will be limited at best. Planting date studies have traditionally been cut off at about July 1, where resulting yields are about one half of a normally planted soybean crop. Experience with soybeans after peas has shown that planting a soybean variety that is at least one maturity group earlier than adapted to the region before July 4 will occasionally produce respectable yields. Producers are seldom content with yields from crops planted a week or more after July 4. By this time, yield potentials fall to 40 percent of normal or less. Therefore, in fields that are a complete loss, replanting soybeans should happen as soon as possible, if at all.
Sources: Jeff Coulter and Seth Naeve, agronomists with U of M Extension.