This week brings a call from a wine grape grower asking if the use of helicopters is among the accepted standard operating procedures in fruit growing regions during Inversion Layer Freezes.
There are two kinds of freezes affecting fruit crops:
|Figure courtesy NCSU
- Advection Freeze occurs when a very dry cold air mass moves into a region with strong winds
- Radiation Freeze, aka Inversion Layer Freeze, which occurs with a very dry local air mass, little or no wind, and a clear sky.
Helicopters have documented efficacy to reduce losses only against Inversion Layer Freezes and are considered part of legal Right-to-Farm protected standard operating practices in the US.
Other methods of protection against freeze include wind turbine machines, heaters and open burning (which requires NJDEP Exemption, as was granted in NJ 2012), water sprinklers, and cultural practices, e.g., moist bare soil in a vineyard makes vines less prone to freezing injury than dry soil with vegetation under the vines.
Air temperatures can be 3℉ to 10℉ warmer at just 50 feet above the ground. The inversion air layer can vary from 30 to 200 feet above ground level. Inverting this air layer with propellers is frequently sufficient to reduce freezing damage and save wine grapes and other fruit crops.
Ag Agent Win Cowgill states that in areas of the US where this is commonly practiced, helicopter pilots and their client farmers may use onboard infrared thermometers or spotters on the ground with thermometers to locate where in the vineyard the inversion layer is present in order for the helicopter and pilot to be most effective. They need to find the highly localized inversion layer above the field for success.
I have heard anecdotally that one helicopter can assist in saving about 25 acres of vines at a time. Win Cowgill reports that in Spring 2012, helicopters alone were responsible for saving about 20% of the fruit crop during a difficult time in the Hudson Valley, NY.
While noise for a few hours from permanently installed wind turbine machines or helicopters might inconvenience–even distress–some residential neighbors near a farm, this is an accepted practice associated with living near the rural beauty, the local food products, and economic agritourism vitality that vineyards provide to communities year-round. Frost protection via propellers is infrequent. But when needed, it needs to happen without delay. It would be a good community courtesy to notify your local municipal police, and health/noise ordinance official on those infrequent times when helicopters are needed to save the vineyard crops in NJ.