HOW TO PROTECT ORCHARDS FROM FROST

Hawke's Bay Herald-Tribune, Issue 139, 29 June 1937, Page 9

HOW TO PROTECT ORCHARDS FROM FROST

USE 0F APPLIANCES Cause and Prevention of Damage EXPERT'S ADDRESS Frotective measures to comhat frost risks were detailed to oxchardists "by Mr N. J. Adamson, Government orchard instructor, in the course of hls address at the demonstratidn orchard en Saturday afternoou. Ahout 80 growers were present. Mr J. H. Milne, president of the Hawke's Bay Fruitgrowers' Association, afterwards demonstrated with different types of oil-burning heaters.

By the use of proper frost-fighting appliances Mr Adamson stated thal heavy losses like those occasioned last season could be prevented. Suitable oibburning heaters, which had advantages over other fuel appliances, would alford almost immunity from frost damage. "Hitherto Hawke's Bay orchardists have not as a whole regarded seriously the fa'-"" that frost is one of the limiting'faetors in* fruit production in the distriet," said Mr Adamson. "This district has always been subject to late frosts of varying intensity, causing some injury to deciduous fruit crbps in ^certain localities. Sometimes it amounts to a slight thinning or a partial loss of crop in poekets, but only at wide intervals has there been a devastating visitation such as was experienced last October. "Loss from fruit damage by frost, injures not only the orchardist but any serious loss is f elt by the whole community. The grower loses income and the necessary. orchard maintenance is likely to suffer as orchard costs have still to be met. Subsidiary industries are put out of gear and the effect is very widespread. Fruitgrowers therefore owe it to themselves and to the community to prevent such loss if at all possible. The recent visitation has been a direct loss of possibly .£S0,000 to the growers themselves and a similar amount to other industries." * Such losses might be prevented by proper frost-fighting appliances, said Mr Adamson. The questipn was under what circnmstances should frost-fight-ing be provided for and the expenso -incurred, and would frost-fighting pay. That might be determined by considering these questions: (1) Is the damage occurring from year to year on a particular orchard suffieicnt to warrant the expense of porteition. (2) Is tho orchard sufficiently remunerative irrespective of frost to make protection worth while. (3) Do damaging frosts occur so frequently as to make the cost of protection too liigh? Certain areas in Hawke's Bay, particularly on the Havelock slopes, Haumoana and Taradale, were aft'ected so little that frost protection nced hardly be eonsidered. There were some orchards of low produetivity that would not carry the extra cost, as the het profit might readily be absorbed by the cost of frost protection. There was" no area where the accurrence of frost was -O iiequent as to make the cost prohibitive. If might saf ely be said that on the flats about Hastings frost ijrotection would pay. The ochardist who could save his crop when others less prepared or indifferent to the position lose the whole or part of the crop was handsomely rewarded by increased pric.es and was usually more than compensated for the cost. Orchard Heating "Frost damage," he said "may be successfully prevented by orchard heating, but the orchardist who wishes to make a success of this work requires at least an elementary knowledge of the physieal conditions which produce frosts and their' general behaviour. A frost is said to have oceurred when the temperature falls below freezing point, 32 degrees F. "We are familiar with white frosts where it is made evident by white crystals on exposed objects. A ' black ' frost is one which occurs when the dew point is bolow freezing and can only occur when tho air is very dry. In our latitudes a frost; is usually confined to the layers of air near the surfacc. A ^freeze' describes the condition when the whole

mass of air is below 32 degrees. "The phenomenon upon which successful frost protection by orchard heating is made possible is known as temperature inversion and may be explained very simply, During a bright day much of the sun 's rays pass through the air witliout warming it appreciably, these rays are permitfed a free passage. ' Tho sun's rays warm the earth's surface, which in t»urn givcs out. certain .rays wliicli do not P^ss so readily through tho air, cspocially if it be rnoist. The lower layers of air are warmed by absorption so the normal state of atmosphere is one of warmth increasing downwards towards the surface of the earth. If long, still, clear nights follow a bright day the soil will continye to radiato heat which the air cannot absorb if it be too dry. Evcntually tho earth 's surface becomes colder than the air resting on it and this air finally loses some of its warmth to the cooler soil. At this stage the lower air has become colder than the layers, 10, 20 or 30 feet up. "This change from the nprmal lapso rate of increasing temperature towards tho earth's surface to the reverso of cooling towards the surface is known as the inversion of temperature, or merojy tlie invei'sion. " That constitutcd a very stagnanf. state of atmosphere, -klr Adamson said. IVitli tho coldOst and densest air in tho lower levels, winds aloft passed over such a stable mass witliout disturbing it, There was no vcrtical circulation because that roquircd a cooler stratum over a wanner one, through which tho c.old air sauk. Witliout wind Jiuil without vertical circulation only one type of movement remains — i,e„ a slow drift of the coldest and densest air near the ground to the lover levels. That gravitative drift saved tlie tops(

slopes to orchardists on .lower levels. That cold air flowed like water and certain places were dangerous owing to the accumulation. (1) The meeting of two valleys where flow may be temporarily checked. (2) Any barrier across the line of drift. (3) Lovel ground at foot of slopes. (4) Natural liollows. Shallow Depth of Air "The fact of inversion and the usua] shallow depth. of cold air and the presence of warmer a-ir immediately abovf make preventive measures possible,'' he said. "One obvious method would be to bring down milder air to mix with lower colder air, which could be dbne at prohibitive cost. The workablo plan is to warm up the cold stratum knowing that the heat • will • not be wasted in the open sky. This is possible for the following reason: Warm air expandg and rises, cold air falls. The upward movement ceases when rising warmer air meets air as warm and light as itself. Hence the warmer air above due to the inversion checks further rising and confines the heating process to the lower levels, approximately dften to the height of fruit

trees. Methods of Heating "Two distinct principles are involved in prevpnting dangerously low temperatures: (1) To cause a smudge to prevent radiation, and (2) by clear heating. • In smudging the procedure is to induce a derise pall of smoke by imperfect combustion of different materials. Since the intention is to conserve existirig warmth 'it 'is essential to star't early in the evening. Wasto of fuel and length of tiine and lower efficiency make smudging less economical than clear heating. "In clear heating the same fuels are used but in^ efficient stoves constructed in Such a way that the rate of heating' may be controlled. ■ With complete copibustion, the more effective clear heating method permits of a later start ' and shorter ■ heating period. In clear heating use is made of radiant heat and heat carried by convection currents in the air. The ascending warm air which stops at its own temperature in the inversion gradually extends the warmer air mass downwards till in envelopes the whole orchard. "In this matter of fuel we have a clioice of solid and liquid fuel, coal, carbonettes and oil fueL These have been subject to fairly successful experimpnt and it should be. possible to com.pare the cost of. the basis of heat production. . However, it. would, be safe to say tha.t the most . convenient and econpmical fuel is fuel oil, and it is tho only one we should consider." Several years. ago,- ho said, the smudge pall became such a public nuisance in California, interfering with shipping, causing grime necessitating scrubbing of . citrns fruits, that citrus growers prefer clear heating. For deciduous fruits a partial smudge may be less damaging with buds. In perfectly clear heating and elimination of smudge, quite elaborate itypes of stoves are 'used. ' Although less efficient, smudging had the advantage of lower capital cost, since heaters of the pail type might be used with or without s'preaders. It was possible to burn ordinary grades of fiiel oil in simple, inexpensive heaters without producing visible amounts of smoke at normal burning rates. " • Critical Temperatures "The danger period may extend from the swelling of buds until sometime after fruit set. Th'e temperatures at which buds will be killed depends on' many f actors that no welldeiined limits can be designated. Condition of tree, stago of buds4 position. moisture in atmosphere, duration'of low temperature and previous weather all have a bearing on frost damage. There is a range of at least 5 degrees between temperatures at which all buds will be killed and that at which only 5 per cent will be lost. If few buds the critical 'temperature is higher than when blossoms are likely to be numerous. If 2 per cent of live buds on peaches femain to mature there will be a fair crop. The critical frost temperature is therefore a relative term depending on the percentage of blossom that mnst be saved. The following table gives what are recognised as safe temperature limits for normal trees in average seasons under usual conditions: — Buds Colour Full Fruit Showing Bloom Set Apples 27 29 30 Pears 28 29 30 Peach t 25 28 30 Plums . . . 30 31 31 Grapei» 31 32 . 32 Apricots . . t . . 30 32 32

"The upparatus consists of oil burners, lighting torchos and rhermometers and alarm sets. Good mercurial thermoniet.ers should bo used .for or'hnarv obv.orvations and should be tested. Mxnlimum thermometers with clear spitit an index needles are very serviceable. Minimum thermometers with coloured spirit are unreliable unless in wooden shelters as thcy may read several degrees 'too low on accOunt of radiation. Minimuin thermometers are placed horizontally and usually placed 4ft. 6ins from the ground under shelters. Eloctrical contact merciirial thormometers are made to ring a warning bell at fixed temperatures, usually 34 degrees. All thermometers should be placed under shelters open to tho south. Severn] are required and it is espoeially nocessary to have one outside the area to be lieated as a cheek. Warning thormometers should be placed at tho lowcst lcvel of the crop to be protected and pielerably in the lowest part of the orchard. Warning thermometers are absolutely essential for safoty. Oil burners should be of the ordinary pail tj'pe with a spreader to regulate tho rate of combust-ion, usually five quart, filled to lin. of the top. — Conuu:npl:ion with opon top, 3 hrs.; con.sumplion with spreader, 4J hrs. "Lighting torchcs consist of n twoquails cylindcr fitted with long spoui with wick in point of spout and Hue brass gauze at base of spout to prevent explosions. Th0 mixture uscci is half benzinn and kerosenePots Per Acro 1 "It is necessary to havo more on the outside of tho area than in the inteiior, and particnlarly on the cust. 1 sidc or -side from which tho drift ; comns lto, a single are 120 may be|

necessary, but less for larger areas. Oi the east side space 9 feet on outsidi row, and on south and north 18 feet On . row* 18 feet inside on N:S. and 6 18 feet apart, remainder of area allov 27 feet. Lighting should be' done bi starting each alternato pot, commenc ing on side from which drift is com ing." - • • Explaining local forecasting and fac. tors influencing frost, Mr Adamsor 1 said that in the case of the atmosphon being humid a frost was less likely Conditions favouring frost were clear diy atmosphere and cairn' or only ligh winds.. Such conditions were found i; anti-cyclonic weather. Frosts shoul be looked for when the barometer wai high' and rising after a period of colc [ southerly weather. If snow has fallci .' on the surrounding country or that ly i ing to the windward," the chances o; i frost were very much increased. Wlier the ground was- soaked with rain tbi danger would be reduced. i ■■ "Besides a fair, experience of loca conditions what is required in this dis trict is a special forecast from tht Government meteorologist, or- perhaps some organised warning scheme amonj orchardists equipped for frosl i lighting, then we may expect some de- , gree of protection against the usua! type of frost experienced, " concludec . Mr Adamson. ' .