Article written by Madeline Wimmer, UMN Extension Fruit Production Educator.
Images: 1) Golf-ball-sized hail that occurred shortly after a harvest event near Madison, WI (Zone 5b) in 2016. 2) Draped hail netting installed over central leader and (3) high-density apple trees at Pine Tree Apple Orchards, located near White Bear Lake, MN (Zone 5a).
Hailstorms and apple orchards
Hailstorms were reportedly an issue for a number of orchards last year and this past season. While hailstorms are extreme weather events that may occur infrequently, the damage can be devastating, sometimes leading to disease issues like fire blight and reduced fruit marketability.
Hail can range in severity and size, from less than pea-sized to as large as golf balls. How much damage occurs can depend on the hail size, along with the duration of the event, fruit growth stage, and overall canopy configuration. When damage happens, insurance options exist to cover hail damage, but insurance payments may not fully cover production costs and still does not solve the issue of crop loss. Thus, prevention can be the most helpful measure to take.
Images: Examples of hail netting installed overhead, which only covers the tops of the orchard block, making it effective against hail damage, although it cannot be used to exclude insect pests.
Hail netting as a prevention strategy
And that’s where hail netting comes in. Hail netting is a physical way to exclude hail and mitigate the damage. For those who are familiar with bird netting, hail netting is similar, but has a much finer mesh (typically 3 mm by 1.5 mm) than netting used to protect against bird damage.
Hail net can be installed in two different ways:
Overhead netting: installed over an orchard block and held up by posts or other structures.
Draped netting: provides full coverage over one or more freestanding trees, or a trellised row of high-density apples.
Both provide barriers where hailstones bounce off the netting and fall onto the ground. However, only draped netting can be used as a method to exclude insect pests. Recent research done at UMN showed that exclusion netting applied after fruit thinning excluded up to 94% of codling moths and 96% of apple maggots in traps under the net. Some growers are even experimenting with applying the netting after king bloom to influence fruit set, which may work best in blocks with single varieties, but has not been fully studied.
Installation for either method takes a good amount of planning and consideration of things like how you’ll fasten it to end-row posts or stakes. Overhead netting can also benefit from tying together individual pieces of netting, which can provides gaps where hail can fall through, rather than pooling and weighing down on specific areas of the netting.
Draped netting will need to be fastened around all sides of the tree canopy when used for insect exclusion, including the bottoms of the net. Some growers have also installed structures like crossbars, or horns, that keep the net extended away from the canopy and prevent shoots from being forced into an upright position.
When used annually, most nets can last 10 years or longer if they’re stored in a dry and cool environment. Just like with bird netting, it’s extremely important to label your nets if they differ in length or width so you can easily match them to the correct rows each year.
To learn more about overhead and draped hail netting, check out the University of Minnesota’s links below.
Hail netting for apple orchards (webpage)
Hail netting in apple orchards (short video)
Climate change and fruit crops: Excluding the elements (9-minute video)
Hail netting for an Organic Apple Orchard at Dream Apple Farm (21-minute video)
Thank you to our farm and ag professional partners for contributions to the UMN Fruit Update series. Non-credited photos in this article were either taken by Madeline Wimmer or within the UMN Extension system.
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