Feb 4, 2021Low-tech strategies for fighting frost shouldn’t be ignored
Rutgers Cooperative Extension Agent Hemant Gohil divides cold damage fighting efforts into two categories: Active and passive.
While some of active methods of resistance are highly effective, they often require expensive and complicated equipment – everything from smudge pots to Frost Dragon devices, helicopter passes and the more popular stationary fans used to stir up pockets of cold air.
Passive methods of frost resistance may not be as flashy but shouldn’t be ignored, Gohil said.
“I like the topic, because not all growers have those equipment,” he said. “These are simple things, but they work.”
Winter weed management
Management of the orchard floor plays an important role in fighting frost.
Tall grass, weeds and debris between the rows and under the trees will trap colder, denser air that otherwise might drain off the orchard floor into gullies and low spots, Gohil said.
A bare orchard floor is also better prepared to absorb more thermal energy during the day, he added.
Cleanup with a mower and/or herbicide before snowfall can pay: Gohil said that combined with drip irrigation, weed-free strips can improve the temperature between 3-5˚ F.
“That could mean the difference between a crop and no crop,” he said.
Irrigation can provide a buffer, slowing the loss of thermal energy.
He added a couple caveats: In a major weather system such as a polar vortex, cold air won’t simply drain away. “That cold air stays there for a while,” he said. Also, irrigating won’t help if there’s a wind faster than 10 mph.
Delayed winter pruning
While growers often prune throughout the winter, another way to manage risk of cold damage is to delay pruning until the worst of winter has passed – after the risk of a freeze has passed.
Gohil acknowledged that most large and medium-size growers start their pruning early in order to use their crews more effectively, but there are benefits for delayed pruning in both apples and grapes until the buds have seen most of the damage they’re going to see. And he highly recommends it in grapes.
Growers who do prune early may find it helpful to not prune all the way down to their target number of buds, or to prune in two passes.
Variety and site selection
Passive frost protection starts at the very beginning of orchard establishment by choosing apple varieties and finding a site with slope.
“If you are going to plant or buy an orchard, then you have a weapon,” Gohil said. “The most effective weapon is site selection.”
Gohil said the site’s slope doesn’t need to be very steep – he’s found that even in orchards with a very slight drop-off, the worst frost damage is still in the lowest corner.
It might go without saying, but choosing varieties appropriate to the local climate is also important. Growers with concerns about cold damage should prioritize cold hardiness in development of new cultivars as well as while selecting the cultivars they grow. For instance, in Gohil’s New Jersey, Rutgers in 2010 released a late-blooming peach variety, Gloria.
Painting tree trunks and vines
Painting graft unions with white latex paint is a way to keep out pathogens, but Gohil said painting the whole trunk is also a way to avoid cold damage. Sunshine can warm the trunk quickly and unevenly.
“White paint, it reflects the light so the trunk of the tree doesn’t get too warm,” Gohil said.
A 50% mix of paint and water is recommended.
— Stephen Kloosterman, associate editor
Photo at top: Hemant Gohil evaluates bloom in Apricot variety block, following a cold event at Rutgers Agricultural Research and Extension Center in Bridgton, New Jersey. Photo: Rutgers