June 22, 2001

Yield Loss From Hail Depends on Growth Stage and Damage

Early season hail storms have struck several areas in North Dakota, causing considerable crop damage. The amount of yield loss from hail damage on small grains depends on the growth stage of the crop, the degree of stem damage and the extent of defoliation, according to a North Dakota State University crops specialist.

Michael Peel, agronomist for the NDSU Extension Service, says small grains in the three to five leaf stage can suffer complete defoliation from hail and recover. "During this stage the growing point is below the soil surface and will not be damaged," he says. "Once the growing point extends above the soil surface it is vulnerable."

Damage to the growing point shortly after jointing will result in loss of production from that tiller. If the damage occurs before the flag leaf stage the plant may initiate new tillers and produce at a reduced level.

Once jointing starts the plant loses its ability to initiate new leaves on that tiller, so defoliation after jointing can dramatically reduce yield, even if the growing point has not been damaged, Peel says.

Hail causes the greatest damage to small grains from the boot stage through later stages. Yield reductions result from both injury to the plant stem and defoliation.

The effect of stem bending on yield depends on the location of the bend and the stage of the crop. Stem bending immediately below the head results in the greatest yield reduction.

Peel says research in North Dakota indicates that stem breakage at heading results in the greatest yield loss in small grains.

Yield reduction from bent stems is progressively less as the crop matures, until the crop becomes susceptible to shattering, he says.

Estimating yield reduction is difficult if a hail storm results in leaf damage without visible stem damage, Peel says. Although all leaves can be damaged during a hail storm, the flag leaf generally shows the most damage. The flag leaf accounts for 80 to 90 percent of the carbohydrate assimilation needed for grain fill, but if it is removed remaining healthy leaves may compensate for its loss.

"Limited research indicates that yield reductions due to loss of the flag leaf is at least equal to that of bent stems," says Peel. "The loss of all flag leaves at flowering may only result in 10 to 20 percent yield reduction if lower leaves are actively photosynthesizing. If other plant parts are diseased or damaged the yield reduction will be much greater."

Both bent stems and leaf damage must be taken into account when determining total hail damage.

"Relatively high levels of stem breakage can occur and acceptable yields obtained if the plant has sufficient undamaged leaf area.

Total defoliation immediately following heading in small grains will generally result in a crop failure. Yield loss due to hail at the hard dough stage and later is wholly a function of shattering and lodging," Peel says.

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Source: Michael Peel, (701) 231-8037, mpeel@ndsuext.nodak.edu
Editor: Gary Moran, (701) 231-7865, gmoran@ndsuext.nodak.edu