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HAIL Hail is not uncommon from spring to autumn at high altitudes, but potatoes are remarkably resilient to its damages compared to other crops as corn and beans. The severity of hail injury, its importance and degree of recovery are dependent on the amount and size of the hail, the growth stage of the plants, the variety affected, the weather after the hail, and practices used. The greatest effect on yield occurs when there is severe hail two to three weeks after tuber initiation or early tuber bulking. For many varieties, this corresponds to two to four weeks after flowering. Leaves tear, appearing tattered, and also have holes through the blades where small hail went through. Damage is similar to that caused by sandblasting. Protecting fungicides application is recommended as early blight and alternata blight can invade. Vines may be partially completely defoliated. If 25% or less defoliation occurs early or late in the season, or 10% or less during mid-season (bulking), there may be little effect on yield with good management practices and cooperative weather. (These are the same defoliation thresholds used scheduling treatment of eating/chewing insects as Col. potato beetle.) Stem injury is the main reason for crop loss due to hail. At the point of impact, hail can break the stem at worst, can go deep enough to cut the vascular tissue and expose it, and, at the least, form a whitish, papery, oval-shaped bruise on the surface. All of these open a portal for pathogens such as aerial black leg. Vine maturity may be delayed due to the recovery period after hail. The application of sulfur as Thiosul through the center-pivot may help in recovery from slight to moderate damage. Tubers are not directly affected. However, mid-season hail reduces yield by inducing late sets resulting in more smaller tubers. Also, mis-shaping of tubers may occur due to erratic growth as the vine tries to recover. Late-season hail may reduce tubers solids (lower specific gravity).
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