Posted  31 Jul, 2017 
In: Articles

Originally published on Alberta Agriculture and Forestry

Unfortunately, hail and hailstorms are almost a given during the summer on the Prairies. Hailstorms are associated with regular thunderstorms, and are typically localized events; however, hailstorms can cover wide swaths of land.

Thunderstorms form when air heats up during the day, rising (because it is lighter) and then cools; the moisture within the air condenses to form clouds. Sometimes condensed water within thunderclouds will become super cooled (cooled to below the point of freezing, without freezing) in the strong updraft winds that are common in thunderheads. Updrafts can keep the suspended moisture from falling. Once the super cooled moisture contacts something to form around (such as dust, ice crystals, etc), a hailstone will be formed. Once the hailstones are too heavy to be held up by the winds, they will fall. The size of the hailstone will be determined by the amount of moisture and the strength of the updrafts.

The overall effect of hail damage will depend on the size of the hail, the duration of the hailstorm and the type and growth stage of crop. Generally, the earlier the damage occurs, the greater potential for regrowth. Yield and product quality will generally be reduced. Below are some of the effects of hail damage on different crops and some of the ways that producers might manage the effects of hail on their crops.

Potatoes
Surface damage to potatoes is typically some amount of defoliation, ranging from leaf damage to complete destruction of leaves and stems. Although potatoes can recover from hail, tuber yield and quality are usually affected. The effect of damage will relate to the amount of damage, the growth stage of the potato, cultivar, as well as subsequent cultural practices and weather.

Loss of foliage greater than 25 per cent will reduce total and marketable yield, particularly if damage occurs before midseason. Greatest losses will result if damage occurs within 2 to 4 weeks of flowering. Foliar damage results in reduced yields, increased number of small and deformed tubers, and reduced tuber specific gravity. Tuber maturity will also be delayed and some foliar regrowth may be observed. Damaged tissues are at risk from attack by plant pathogens, particularly soft rot bacteria.

To manage the crop after damage, the key is to ensure that the crop is not stressed further. Apply protective fungicide applications to the crop. Ensure that there is adequate fertility; however, high levels of nitrogen can enhance foliar growth, perhaps at the expense of the tubers. Be prepared to adjust harvest dates based on how the crop recovers.

Root crops (carrots, beets, etc)
Foliar damage will reduce photosynthetic capacity of the plants and may reduce yields, depending on how early or late the damage occurs. Most root crops will be protected from direct damage, but grade and cull thoroughly at harvest in case of shoulder injury, which may lead to increased levels of storage rot.

Bulb vegetables
These crops are especially sensitive during early growth stages however, at all stages, leaves and neck areas may have whitish/yellowish spots or leaves may be shredded completely by hail. Replanting young crops may be necessary, whereas fungicide applications can protect older crops from infection by fungal and bacterial pathogens.

Leafy greens
Leaves may have some slight holing or may be completely destroyed. These generally short season plants have the potential to recover quickly from damage, depending on the stage of growth. If the damage appears to be minimal, wait it out and clean up plants during harvest by trimming unmarketable portions. If plants are young and heavily damaged, consider replanting. Disease susceptibility will be increased, so consider a fungicide spray.

Fruiting vegetables (tomatoes, peppers, cucurbits)
Similar to other crops, foliar damage can slow growth and reduce yields. Physical damage to developing fruit can reduce quality and marketability, depending on the type of crop. Some wound healing and subsequent scarring is likely on thicker skinned crops, but this may not affect marketability. Wounds on leaves and fruit represent a doorway to invading pathogens. Fungicidal sprays can help protect damaged fruit.

Fruit & Berries
Damage can include foliar injury (ranging from slight leaf holing to complete defoliation), as well as branch breakage in larger trees and bushes. Injury to fruit can include bruising, scarring, holing, as well as fruit being physically knocked off of the plant. Defoliation can result in delayed fruit maturity or potentially excessive lateral shoot proliferation. Wounded plant parts are susceptible to attack by pathogens such as soft rot, canker, etc.

Remove broken or damaged plant material. Apply registered protective fungicides if necessary. Pick damaged fruit and utilize quickly.


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