Putting a Roof Over the Orchard – Hail Netting

One of the most common photo shots brought back to North America by travelers wanting to learn more about European fruit production is the shot with apple trees under hail netting. In fact, some areas of Europe are almost entirely netted because of a 100 % probability of destructive hail on an annual basis. Growers in some regions of Europe cannot get production contracts unless they are under netting.

This high probability of hail in mountainous regions of Europe is rooted in historical records and the ever-present factor of dramatic changes in elevation and air temperature from the floor of any given valley to its nearest mountain range. It’s the mixing of cold air coming off the mountains with the warm air thermals coming from the ground that causes the hail. There are some very obvious advantages with the netting.

In Ontario, the use of hail netting is a fairly new concept. However, where high value cultivars are grown in a vertical axe planting, the post and wire structure is basically already there. It just has to be built a little higher using a retrofit of existing posts or by using longer posts (16 foot) in order to get a ridge wire at the 12-foot mark above the row.

The netting appears to be good for at least 12 years and is left in position year round with nets rolled up onto the ridge wire during the winter. In other words, once the netting is up, it stays in the orchard. Light coloured netting is preferred at this altitude to minimize reduction in light intensity under the canopy. The netting may also take some stress off the trees under high heat and UV conditions. Netting in Europe is reported to last in some cases up to 20 years.

Included in the suite of benefits is the obvious reduced risk from hail damaging the crop. Other benefits could include reduction or elimination of fireblight from trauma events caused by wind or by hail for instance. Bird damage could conceivably be reduced and a certain amount of insect pressure could probably be eliminated because of the fineness of the mesh. Sprays applied to the canopy would probably stay in place longer and not suffer displacement from rainfall. Spray drift could potentially be mitigated as well.

Like an investment into irrigation systems, hail netting costs look pretty scary at first but when these costs are spread over more than a decade of usage, they become more rational.

The actual netting is interesting from a tensile strength perspective. It doesn’t stay flat and smooth during a hail event but stretches and gives to accommodate the weight of the pellets, which can be considerable. At some point the net will dump the ice harmlessly between the rows and reload if the hail lasts any amount of time. The general look is that of a peak and furrow configuration as the pitch plays an important part in shedding the hail that’s trapped. What we don’t know and can only speculate on at this time is the overall effects on microclimate under the netting. This may include changes in drying times form wetting events or an increase in humidity from the separation of air masses on each side of the roof. Look for increased interest in hail netting as a risk management tool for orchardists and apple growers in particular here in Ontario and the Northeast.

In talking with Mark Lucas at Gintec Shade Technologies Inc., an Ontario supplier of netting for various agricultural purposes, he stresses that planning is key to getting started with netting. If you want to do something in 2005, start the process now. The netting itself is custom made to fit the planting. Most of the cost is in the perimeter hardware according to Mark. This is understandable because it’s the ends and sides of the planting that secure the wires etc.

Mark estimates the costs at around $ 8,000.00 per acre. This includes posts, wires, hardware, and netting. This cost can vary and could go down with larger plantings. In other words the bigger you go the less cost per square foot. The actual netting required for an acre is about 10% greater than the square footage of an acre to allow for the dimension of ridge and furrow.

The Italians pioneered much of the technology in use regarding hail netting. This is a result of the need to secure supplies of fruit in risky areas for cooperatives to forward contract with buyers in the rest of Europe.

Figure 1. Retrofitted vertical axe endpost. Set up for hail netting.