Hail

While a relatively uncommon event, hail poses a significant threat to tree health. Hail forms when super-cooled water droplets collide with tiny ice crystals. Strong updrafts produced during severe thunderstorms can keep hail particles suspended in the atmosphere for long periods of time allowing them to grow to sizes in excess of several inches in diameter. The speed at which hailstones fall varies with size; a small stone can reach speeds of around 25 mph, but larger stones can hit the ground at speeds in excess of 200 mph! Even a small, relatively slow moving hailstone can cause severe damage to a tree. Foliage is easily bruised, shredded and/or stripped from trees during hail storms. Hailstone impacts on the stem, branches, and twigs can easily kill the underlying cambium tissue, resulting in a necrotic canker. Widespread cankers can cause branch dieback and severely stress a tree, making it susceptible to attack by secondary insects and pathogens. Wounds caused by hailstone impacts often serve as infection courts for many bacterial and fungal diseases.