Weather risks: strategies to mitigate the risk of hail injury
Information for apple and tender fruit growers to assess and mitigate damage caused by hail.
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This in the 4th in a series to help apple and tender fruit growers in Ontario assess the weather risks that can damage their trees and crops. It is important to recognize the weather risks at each location, and develop strategies to reduce or eliminate the impact on your business operation.
What it is
Hail is a solid form of precipitation. Hailstones are formed when water droplets moving upward through clouds, encountering temperatures below freezing, causing the water to supercool and freeze on contact with condensation nuclei like dust particles. Hail is often associated with thunderstorm activity and changing weather fronts. The pattern of hailstorms moving across a region often follow the same path, although recent events have surprised growers when hail moves in from an unexpected direction. Hailstones are usually layered, sometimes with sharp edges and range in size from pellets to golf balls or larger. The intensity and duration of the hailstorm will determine how much damage is done.
When it occurs
Hailstorms often occur under hot, humid unstable weather conditions in the summer, although damaging storms have occurred in every month of the year. Generally, they occur in late afternoon or early evening when thunderstorms build up, but again, damaging hailstorms have occurred in the night or early morning as well. Growers who are using hail-altering technology need to be alert to hail development at any time of the day or season.
Where it occurs
Hail damage is an all-too-common weather risk for tree fruit growers, with some acreage hailed during the growing season every year in Ontario. Unfortunately even a short episode of hail can cause severe injury to fruit and trees, both downgrading quality and causing subsequent issues with diseases like fire blight, cankers and fruit rots.
Mitigation strategies to consider
Some of these may help reduce or eliminate damage due to hail:
- Production insurance (PI): Production insurance can be purchased well before the hail season, and can give you peace of mind that at least some of your input costs will be covered if it hails. Your premiums will depend on the coverage you choose, your claim history, and the yield potentials of your orchards. Over time, your premiums can be reduced if you are lucky enough not to have claims. However, some growers struggle with the premium costs (especially in their start-up years or if they have claims) and the fact that PI is not intended to fully cover your loss, either in yield or price. There is also the problem of reduced coverage levels in the years after your crop is reduced, due to the effect of the loss on your long-term average yields. Also, for all crops except apples, spot loss insurance is not available, so growers with multiple orchard sites may be penalized when good yields occur on the non-hailed sites.
- Hail Netting: Many areas of the world cover all of the acreage with nets, especially where hail occurs every year, and sometimes multiple times a season. A few Ontario growers have installed hail nets, which consist of the tall post system, supporting overhead wires, that support a light-weight netting over each row. Growers using trellis only need to use taller posts. The nets attach between each row to allow accumulations of hail to drop safely to the orchard floor and avoid fruit damage. Hail netting needs to be pulled over the trees before fruit set, and pulled back after harvest to avoid winter damage to the netting. Hail netting can be 100% effective, but the cost of erecting and installing nets restricts its use to high-paying varieties. Growers have noticed that temperatures are reduced under the nets and winds calmer, so that orchard operations including spraying can continue longer.
- Hail-interrupters (cannons): These machines fire explosions of sound waves up into the upper air layers above your orchard. The machines need to be started well in advance of oncoming hailstorms. The theory is that the sounds waves fired into the air interrupt hail formation, resulting in non-damaging slush, but this is difficult to prove scientifically. Hail cannons are expensive, need to be installed well in advance of hail, and require constant monitoring of weather patterns and predictions. They are noisy and irritating to neighbours, and require ear protection for nearby workers. A good supply of acetylene is needed in stormy seasons.
- Multiple orchard locations: : Generally early blooming cultivars are more susceptible to frost damage, simply because most frost events happening earlier in the season. In 2012, we noticed that Honeycrisp, Golden Delicious and Ambrosia tended to bloom later, and produce some crop even on frosted sites. This is not always feasible due to your climatic location, market demand, or length of growing season, but needs to be considered.
Avoiding or reducing hail damage is an ongoing challenge for many fruit growers. The extensive damage from a short period of hail is discouraging, and the subsequent damage from fire blight, canker and other diseases can be devastating. As weather patterns become more erratic and produce more hail events, growers should consider more than just plain luck to reduce their risk from hail. The investment in intensive orchards and high-valued varieties may encourage more investment in hail strategies in the future.