Issue link: http://read.dmtmag.com/i/105709
Frost protection strategies There's nothing like a disaster to focus attention on ways to prevent freezes. put him on the speaking circuit, where he gave growers the benefit of his accumulated experience. He spoke at the Great Lakes Fruit, Vegetable, and Farm Market Expo in Grand Rapids,Michigan, to an audience that, after a year of ill-timed freeze events, was primed to learn what it could. "Often times, you only need one or two degrees, and it's the difference between crop and no crop," Evans said. "No frost prevention system is going to be perfect, but you can minimize the damage." On the other hand, he said, if you're willing to pay enough, "Any crop can be protected against any cold temperature event if economically warranted." Total coverage in a heated greenhouse is safe—but expensive. The objective of any crop frost detection system is to keep plant tissues above their critical temperatures, which is the temperature at which tissues will be killed, Evans said. This temperature varies by stage of plant development. Evans said that growers should approach frost protection systematically, proceeding step by step, adding increasing protection as they need and can afford, starting first with passive methods that avoid frost damage. "The best time to protect a crop is before it is planted, and site selection is the most effective passive risk avoidance strategy," he said. —Robert Evans "One of the best ways to improve the effectiveness of active frost protection methods is to understand where the cold air drainage moves into and out of a block. Windbreaks, buildings, stacks of bins, road fills, fences or other barriers, tall weeds, all retard cold air drainage and can cause cold air "The size of the potential cold air pond will likely be four to five times greater than the height of a physical obstruction." by Richard Lehnert T ree and vine crops can be won or lost because of one or two critical degrees of cold temperature, so, ultimately, the best method of frost protection is good site selection. But even the best sites won't be perfectly freeze-free. Is there a good way to recover those one or two degrees lost on a cold night? Research agricultural engineer Dr. Robert Evans, who recently retired from the USDA's Agricultural Research Service's Northern Plains Laboratory in Sidney, Montana, spent his career studying ways to do that. Before his work at USDA, he spent more than 20 years doing frost protection research at Washington State University. Weather events in the eastern United States this year Frost protection methods—costs and other considerations Burning organic material Wind machines/ fans Cold air drain Helicopters Depends on air movement Oil‐fueled: 40 heaters/acre Propane‐fueled: 60 heaters/acre Approximately 10 acres Large = 40 to 60 acres, smaller = 25 to 40 acres Approximately 10 to 13 acres limited by well size (35 GPM for 10+ hours) uniform NA Oil, diesel or propane Gas, electric, PTO Fuel Gas, electric, PTO, diesel (most new are propane) Electric NA Cost of old hay bales or brush piles is usually minimal Oil‐fueled: approximately $50 each = $2,000/acre Propane‐fueled: approx. $100 each = $6,500/acre Approximately $13,500 Rental cost: large = $1600 per hour per bird, small = $700 per hour (plus travel & fuel time) Approximately $16,000 to $35,000 Well, irrigation system plus extra $1,000 per acre for microsprinklers $10 to $25 per acre NA Oil‐ and propane‐fueled: 1 gal./hr/heater Approximately 1 gal./hour Included in rental Approximately 13 gal./hour Electricity cost Fuel for tractor Cost of old hay bales or brush piles is usually minimal Movement to site Cost to move— grower installed Minimum hours for standby Concrete pad plus installation (often included in total unit cost) Added on to irrigation system install costs Operator's time Managing to burn Significant— heaters should be cleaned after 20 to 30 hours of use Minimal: owner maintained NA if hired in Can be covered under contract, but mostly minimal unless a gearbox goes Adds more time for microsprinkler care than regular trickle irrigation Some materials are hard on sprayers NA NA Yes NA Yes Yes? NA Yes: wind machines Yes: wind machines Yes: wind machines, sprinklers, heaters ? Yes: heaters Perhaps Perhaps Quiet factor Yes, but can cause smokey conditions Yes, but can cause smokey conditions No (63‐66 dB) Not really No (90 dB) Yes No (sprayer/ tractor noise) Special weather concerns Not in high winds or dry conditions Yes Yes Less coverage if it is very cold. They can move vertically to find the warm air inversions. Yes/No Yes No Recycling NA NA For fun, if you fly one Might help with fruit finish Irrigation in summer. Cooling effect during dormancy to retard bud break? NA Coverage Power options Unit cost Fuel consumption for one hour Installation cost Maintenance cost Auto start available Enhances other frost protection Dual usage factors Microsprinklers Sprayable frost materials Heaters SOURCE: Amy Irish‐Brown, Michigan State University Extension www.goodfruit.com GOOD FRUIT GROWER FEBRUARY 1, 2013 39