When injury occurs near or after flowering, the plants usually remain green and continue to live but do not produce seed. The effect of bruising by hail stones is difficult to determine. If the amount of stalk bruising is such that the plant does not weaken or break during the remainder of its development prior to combine harvest, the effects on yield may be minimal. Stalk injury of such magnitude or at a specific location on the plant resulting in non-harvestable heads certainly would have an effect on yield. Physical injury by hailstones on the back of a sunflower head at or near anthesis can result in Rhizopus head rot, especially if wet or humid conditions are present.
Physical injury can occur as a result of bird, insect or hailstone damage.
Increased dead plant tissue resulting from a hail storm, especially on the back of a head, may increase the chance of white mold infection.