Good Fruit Grower

February 2013

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&! ) $(" &! (&) $(" +, -$& .($- ( ').(- )( (1 / $& & +.(($(" " + $ )0 )- -)+ )0 #.--& ). & )+% +).( )" " "! +),- ( )()'1 !)$(- )+%, )$(- $ $!- # ! " ! )(/ 1)+, + $"#.+ ( 1& ( *+ 1 +, ;;; 4,-0&63;2;)0(-2+ '31 > )77 8,%2 -2',)7 ;-() *36 2%663; 86)) 63; 74%'-2+7 > !6%'836 13928)( :%0:) -7 %:%-0%&0) > =(6%90-' (6-:)2 6300)6 ',%-2 *36 032+ 71338, 34)6%8-32 > "7)7 )<-78-2+ 86%'836 ,=(6%90-' 7=78)1 > (.978%&0) ,-8', *36 (-**)6)28 (6%;&%6 ,)-+,87 > )%6 13928)( %9831%8-' &3< 7834 83 46):)28 70-(-2+ Building the Best Since 1964 PHIL BROWN WELDING CORP. ,32) • %< • ? -0) ( $ 32/0-2 -',-+%2 Contact Vine Tech Equipment your Northwest Phil Brown Dealer ;;; :-2)8)',)59-41)28 '31 to pond in areas behind them. The size of the potential cold air pond will likely be four to five times greater than the height of a physical obstruction." Vegetation in an orchard, or weeds around the edges, can slow or stop the movement of cold air out of an orchard. Windbreaks, he said, put in the wrong place, can do more harm than good for frost events. Other passive measures include choosing lateblooming varieties and training and pruning trees so the bearing surface is up away from where cold air accumulates. Growers may not love ladders, but on frosty sites, fruit is mostly located where lad—Robert Evans ders reach. "There is probably no way to economically overcome poor site selection," Evans said. "There is probably no way to economically overcome poor site selection." Use of water Active frost management techniques involve: 1) adding heat to the environment using water or heaters, 2) mixing the air to move heat into the orchard, or 3) conserving heat by not allowing it to escape. Growers need not select one method only. The effects may be additive. They can expect to gain four to six degrees of protection from overhead irrigation, one to three degrees from undertree irrigation, and one to four degrees from orchard heaters, wind machines, or helicopters. When using more than one method, the order would be to choose water first, then add wind, and, finally, add heaters, because of cost. One of the best ways to add heat is through applications of water, he said. "Water-based methods are generally the most economical. Heat from water is also more efficient because it is released at low temperatures into the environment, is less buoyant, and may selectively warm the coldest plant parts." Water-based frost protection systems can also create problems with disease, saturated soils, runoff, and leaching of nutrients and other agrochemicals. And overtree sprinkling is risky and, if not done properly, can cause more damage than it prevents, and even destroy an orchard. Water has interesting properties. Heat is released as water cools or changes phase from vapor to liquid or liquid to ice. The change from water to ice releases 1,200 BTUs per gallon. The condensation of vapor as fog releases 9,000 BTUs of energy per gallon. These are much greater amounts than released by mere cooling of the water. Dew point High dew point temperatures are also extremely important to the success of a frost protection program, he said. When dew points are high, water condenses when it is warmer, and this condensation provides a huge amount of free heat on the coldest parts of the plant. This free heat is not helpful if it is released when temperatures have already plunged to damaging levels. "Overtree sprinkling can provide the highest level of protection of any single available system (except field covers/greenhouses with heaters), and it does it at a reasonable cost," Evans said. It is the only method that does not rely on inversion strength for the amount of protection, and it can provide some protection in advective frost conditions, he said. "The applied water must supply enough heat by freezing to compensate for all the losses due to radiation, convection, and evaporation," he said. "Consequently, 40 FEBRUARY 1, 2013 GOOD FRUIT GROWER www.goodfruit.com

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