FROST-PREVENTION FOR ORCHARDS.

New Zealand Journal of Agriculture, Volume XXXVII, Issue 1, 20 July 1928, Page 19

FROST-PREVENTION FOR ORCHARDS.

( Continued.)

W. R. Lloyd Williams,

F.H.A.S., Orchard Instructor, Alexandra

II. FROST AND ITS OCCURRENCE

The fruitgrower who successfully controls disease in his orchard is one who knows something of its nature and methods of attack. In the same way, any one making an endeavour to prevent damage to his orchard or garden by frosts should at least have an elementary knowledge of the physical principles involved in the production of frost before he can hope to make a success of orchard heating.

When the temperature of the air falls below 32 0 F. there is said to be a frost. A frost may be a “ white frost/' when it is made patent by the appearance of crystals of ice or hoarfrost on exposed objects, or a black frost’’ which can only occur when the atmosphere is very dry. In a black frost the dew-point is below the air temperature at the time of the frost. As is more fully explained below, a frost in temperate latitudes is usually confined to the layers of air near the surface. If the whole mass of the air, including that in the higher layers, is below freezing-point the condition is described in America as a “ freeze.” A freeze may accompany either a black or a white frost.

Temperature Inversion.

Should the day be warm and sunny ' the ground-surface is heated very considerably by radiation from the sun until its temperature becomes higher than that of the air in contact with it When this occurs the latter is warmed by conduction of heat from the ground. This heated air rises, and is continually being replaced by cold air from above. The former continues to rise until it reaches air of the same temperature as itself. Any layer of cold air near the surface is thus gradually warmed up, so that by the middle of the morning the temperature of the air is highest near the ground. This state of affairs continues until about 3 p.m., when the amount of heat radiated from the ground begins to exceed that received from the sun and the ground temperature begins to fall. Soon the ground begins to cool the air in contact with it, thereby reversing the order of things and making the air near the ground colder than that' higher up.

Fortunately for the grower intending to heat his orchard, atmospheric cooling does not usually extend to great heights, the temperature rising from the ground upwards until a height is reached when there is very little variation. This phenomenon is known as “ temperature inversion,” and is what makes orchard heating possible. The feasibility of heating depends on the existence at a moderate elevation above ground of a layer of air which is above freezing-point. With the same ground temperature, heating will be -easier the more marked the inversion. The warmed air from the heaters rises, at the same time imparting heat to the surrounding air, until it reaches a height where its temperature is the same as that of the air with which it comes in

contact. The level at which the temperature of the surrounding air is higher than that of the heated air forms a “ ceiling ” or “ blanket ” which the heated air cannot penetrate. The process of heating, therefore, needs only to be carried on until the temperature of the air below the inversion is all above freezing-point or whatever is regarded as the dangerous temperature. It is not necessary to “ heat the whole atmosphere as many people think, but merely the• layer below the “ceiling.” The inversion will be more or less pronounced according to the weather. If a strong wind is blowing, the different air-layers are mixed together and there will be no. inversion. If the sky is cloudy the ground does not lose so much heat by radiation, so that the inversion is poorly . developed. If a low temperature is experienced under these circumstances, therefore, heating is likely to prove difficult. On the other hand, the clearer and the stiller the atmosphere and the warmer the previous afternoon the more pronounced is the inversion likely to be. It is clear that in a freeze,” even if there is an inversion, heating must prove impracticable. • The heating can be carried on until the inversion is removed, but thereafter the heated air will rise indefinitely and be carried away, while the body of the air still remains below freezing-point. It is possible that there was a freeze on the occasion of Field Test No. 3 (recorded in last month’s Journal).

Several experiments were conducted to test the temperature inversion. (1) Temperatures were taken by Mr. Glasgow in a deep well-like hollow at the north-west corner of Mr. Bringans’s orchard, betweenit and the dredge tailings.- The hollow was some 35 ft. deep, cone-shaped and about 60 ft. across at the top. Following were the results, the figures representing degrees Fahrenheit. .

(2) On the night of 10th September, in conjunction with Mr. Glasgow, a more comprehensive test was arranged, the Alexandra Fire Brigade kindly allowing us the use of their practice stand and ladder in the recreation reserve for the purpose. Temperatures were taken regularly from midnight to 7 a.m. The thermometers, fully exposed, were placed at the following heights from the ground : (a) 1 in., (&) 1 ft., (c) 4 ft 6 in., (d) 10 ft., (g) 18 ft. From the accompanying graph (Fig. 13), which shows the temperatures recorded by each instrument at the times indicated, it will be noted that the lowest temperatures recorded were — (a) 26-8° F., (b) 26-0°, (c) 29-2°, (d) 30-9°, (e) 32'5°. In other words, at 1 in. there were 5'4 degrees of frost; at 1 ft. there were 6 degrees, at 4 ft. 6 in.' there were 2-8 degrees at 10 ft. there were 1'i degrees; and at 18 ft. from the ground the temperature was half a degree above freezing-point difference of 6'5 degrees between the 1 ft. and 18 ft. levels. The fact that the lowest thermometer read

somewhat higher than that next above, was probably due to some defect in the instrument or its exposure.

(3) Tables 4 and 5 (last month’s article) show differences in readings between thermometers A (4 ft. 6 in. level) and A/14 (14 ft.), up to 2| degrees, while Table 4 also shows thermometers F (4 ft. 6 in.) and F/14 (14 ft.), inside the heated area, with differences up to 3| degrees, these figures are despite the fact that the thermometers at 14 ft. were fully exposed and the others were under ordinary shelters.

Factors influencing the Occurrence of Frost.

(l) THE WEATHER.

This aspect may best be -introduced.here 'by reproducing the following extracts' from an article on the “ Protection of Orchards from Frost,” by. Dr. E. - Kidson, in the New Zealand, Journal of Science and, Technology for November last : —

If the atmosphere is humid frost is less likely. The dew-point is the temperature at which the air would be saturated by the existing amount of moisture the temperature at which it would be unable to take up any more moisture by evaporation. _ The minimum, temperature is not likely to fall much below this, for once the dew-point is. reached any further fall results in the condensation of water vapour. In the process of condensation it gives off a large amount' of heat, and the fall of temperature is consequently checked. If, further, the temperature is low enough to cause the condensed moisture to freeze, still more heat is evolved. It is therefore difficult to cool the air much below its dew-point. Frequently when the dew-point is reached a ground- fog will be formed, and this itself will tend to protect the trees from frost-action.

The cold air in the surface layers, being dense, or having a greater weight for the same volume than the warmer a few feet higher above the ground, will tend to flow over a land surface very much in the same way as water does. It will flow off the ridges into the gullies, and flow off sloping land into 'the valley-bottoms. On slightly undulating country it will collect in the hollows, producing what are called in America " frost pockets.” Regions which receive the drainage ■ from a large, cold mountain area, especially if it is snow-clad, will be more liable to damage than others. A gentle slope will be less frosty than the plain below. On a slope the ridges will be warmer at night than the hollows.

In some positions, such as a narrow gorge, the currents of cold air will converge until a moderate . wind is caused, and the air-turbulence produced by the wind will result ' in the warm air from above being mixed with the cold surface layers, and a considerable rise in temperature will follow. Such a site may not, therefore, be as subject to frost as most of the surrounding country. There are several instances of this state of affairs in Central Otago. Cold currents may be deflected by steep hill-slopes, and so pursue a somewhat erratic course over the ground. It must be remembered that, owing to the decrease of temperature with height, the higher the altitude of a locality above sea-level the more it will, in general, be subject to frost.

The conditions .which favour the production of frost are a clear, dry atmosphere and calm or only light winds, which at the same time allow the earth to radiate heat freely through the night sky, and the air which is cooled by contact with the ground to collect in a cold surface layer. Such conditions are found practically only in anticyclonic weather.

The weather in New Zealand is produced by a series of low-pressure waves or barometric depressions followed by areas of high pressure or anticyclones, all moving from the westward. As a depression approaches from the Tasman Sea the barometer will fall, and the winds will generally be from some northerly direction. Since they blow from, lower latitudes, they bring warm and moist air with them. When the area of lowest pressure, or the "trough” of the depression, has passed there will be. a change to southerly winds, which is usually fairly sudden. The southerly winds, coming from higher latitudes, flood the country with cold air. During this stage the barometer rises, and the weather, which has been generally wet and cloudy during the. period of low pressure, gradually clears. As the crest of the wave of high pressure or the centre of. the anticyclone approaches the winds fall off. The weather then will generally be clear, calm, and cold, especially over inland areas, and in the proper season frosts are likely. Frosts should be looked for, therefore, when the barometer is high and rising after a period of cold southerly winds. If snow has fallen on the surrounding country, or that lying to windward, the chances of frost are very much increased. On the other hand, if the ground is soaked with rain the danger is reduced.

The following remarks made by Dr. Kidson in a letter to the writer are also interesting and instructive : —

It is noted that the damaging frosts generally seem to be preceded by falls of snow or hail. There are various reasons why this should be so. First, these phenomena indicate low general temperatures. Hail also indicates a rapid fall of temperature with height, and therefore a cold upper air. Clear, still conditions are likely to follow these phenomena. Second, the snow surface radiates freely, and would produce cold air, which would drift down from the mountains. Third, a snow surface is about a fourth or a fifth as efficient a user of the sun's heat as a grass surface, so that there is not so much heating of the air during the daytime when the snow is about.

In the Alexandra district, which is near the foothills of the mountains, and in a region which is very broken, there appears to be comparatively little stagnation. There is, probably, also a considerable Fbhn effect, producing relatively warm conditions. This is indicated by the warm temperatures, which it experiences in spring for a station at such an altitude and in so high a latitude. Also, where there is a concentration of wind-currents, as in the Cromwell Gorge, these are sufficient to prevent severe frosts. Some such explanation is needed, too, to account for the fact that apricot-growing is so successful in the district. The critical months, September to November, especially the two last, are months in which strong westerlies prevail. The Fbhn effect is therefore likely to be considerable. The liability to frost is consequently rather lower than in the Hastings district, where the mountains are more distant and lower, while the westerly winds are not so strong'. In the Manuherikia Valley and the Upper Taieri there are more chances of stagnation and frost ; in the Manuherikia because its is a wide valley in which the down-dropping winds have space in which to die down, and in the Taieri because; in addition, it is too far east for the Fbhn effect to be felt to the same extent. These facts,' while explaining the relative freedom of Alexandra from frost, also make it probable that temperature inversions are not likely to be so pronounced as in plain country, and that heating will be more difficult.

The Fbhn wind mentioned is a warm wind from higher levels. Its warmth is accounted for by the increased pressure to which the air of which it is composed is subjected at the lower levels. At 5,000 ft., for instance, its temperature may be freezing-point, 32 0 F., and the pressure 25 in. When it reached sea-level its pressure would be about 30 m., and its temperature would be raised to 59 0 F. The effect is the same as that experienced when you pump up a bicycle - tire. The tire and pump get hot.

Many of Dr. Kidson's- references have a very direct local bearing —for instance, the absence of damage in the Clyde-Cromwell gorge through which the Clutha River runs. Again, the formation of “frost pockets is probably one of the main reasons why portions of Mr. Bringans's and adjoining orchards are almost invariably more or less frosted. Also, the reference to a gentle slop being less frosty than the plain below was well exemplified in' the 45-acre orchard of Mr. R. T. Symes at Fruitlands. In this instance, on the lower portions the whole crop was frosted ; part-way up, where the ground rises, a part crop was left ; " while ' at the, top end, where there is a sharp rise, a full crop was harvested.

It has been stated, quite unscientifically, that damaging frosts never occur with the wane of the moon. Local experience last season was most interesting, and should refute such a misleading statement. , There were frosts on the following 'mornings, the state of the moon being shown in parentheses : 28th August (new moon; 27th August) ; 17th September (full moon, 12th) ; 5th October (first quarter, 4th) ; 25th October (new moon, . 26th) ; 14th and 15th November- (full moon, 9th).; 8th December (full moon, 9th). As will be noted by the experiments, the. worst frost was that on 14th

November, followed by a less severe one the following day, when the moon was- on the wane.

COVER-CROPS. The question of cover-crops (or a cover of grass and weeds) appears to be a debatable one which requires further investigation. Several instances have been noted or brought under my notice which might lead one to believe that there is more danger where the ground is covered with a crop than under clean cultivation. These cases may be coincidences, and therefore it is wise not to be dogmatic on the subject until further looked into. 'Mr. P. A. Royds, an Alexandra tomatogrower, had one row of tomatoes on the south-east side of his patch, beside long grass, badly frosted by one of the earlier frosts, while the rest of the plot was untouched. The row was replanted, and was again badly frosted on 8th December, while the adjoining rows, although damaged, were not nearly so bad ; at the same time the row at the other end of the block (north-west side), right alongside some green oats, was also badly frosted. Mr. Royds states that ' he always finds strawberries to be worse frosted in weeds than under clean cultivation ; this happened in a nearby garden (Turner's) last season. He also states that some years ago . one orchard in grass (McLean’s) was the only one frosted, the surrounding ones being cultivated. At Mr. M. P. McGinnes’s orchard, Earnscleugh, there are two long rows of Roxburgh Red apricots side by side, with a strip of grass running along the side of one of them. The latter row showed a light crop, while the other, only a few feet away, carried a good crop., Some orchards under cover-crop in the Earnscleugh district were appreciably damaged by frost while an adjoining cultivated one (certainly on slightly rising ground) received little injury. On the other hand, temperatures taken by me at 1.45 a.m. on 5th October, at 2 ft. 6 in. above the ground, registered alike —29 0 F. —on ploughed and unploughed ground, showing that further investigation is necessary.

SHELTER.

The matter of shelter forms a most difficult problem. It is generally accepted that the few rows of orchard trees on the leeward side of a windbreak are less injured by frost than those further away. This was noticeable at Mr. Hinton’s orchard, the few rows near the road (southern) boundary, on which there is a poplar shelter, were not damaged- as much as those a few rows away. At the same time it must be borne in mind that on the windward side the frost, will be more severe. ■ Moreover, shelters are likely to interfere with air-drainage, which is so essential in keeping the air moving and so preventing a frost. Much thought must be given .the subject before providing shelter against frost, for the frost may not come exactly from the same direction each time, with the result that a shelter may prove the reverse and act. as a stop-bank to prevent the outflow of cold air.

IRRIGATION.

Running water, which gives off heat as it cools, affords only a small amount of protection. If, however, no other means are available Californian authorities advise the running of water both day and night

during the whole period of the frost, but that it should only be looked upon- as a means of partial rather than complete protection. In Mr. Royds’s tomato patch last spring it was noticeable that the portion irrigated was only slightly frosted, and that the drier parts were frosted out, although some plants on the slightly higher ground in the driest part were untouched. ■ .

III. ECONOMIC FACTORS.

Injurious Temperatures.

Unfortunately, we have no local data sufficiently reliable on which to base an estimate of the temperatures which cause injury, and must therefore, in the meantime, rely upon American experience. The following extract is taken from Bulletin 398 of the Berkeley College of Agriculture of the University of California :—

The fruit-buds of nearly all deciduous fruits are extremely susceptible to damage during the period of from twenty-four to forty-eight hours before they open. The petals are still folded, but the flowers are growing rapidly and are extremely tender. Buds in this condition are often injured by temperatures as high as those given in the table for small green fruits. Fortunately, most deciduous fruit-trees come into full bloom gradually, so that even if all the buds about to open at one time are killed, the size of the crop is not reduced materially. Buds of the Bose pear often open simultaneously, and a low temperature just before the flowers open sometimes destroys most of the crop.

At the time generally designated “ full bloom ” most deciduous fruit-trees have large numbers of fruit-buds which are still tightly closed, in addition to the flowers which are fully open. This makes the loss of the entire crop, or even the greater portion of the crop, on one cold night, extremely improbable at this stage. This has led fruitgrowers in some districts to believe that frost can do no damage before the fruit has set. Some growers even follow the hazardous practice of leaving heaters unlighted on frosty nights during this period. While a single frost at full bloom seldom affects. the size of the final crop, a series of heavy frosts, each killing a portion of the blossoms, may leave too few undamaged buds or blossoms for a full crop.'

The most dangerous stage in general is after all the petals have fallen and the fruit has set. All the fruit being in nearly the same condition, the entire crop may be' killed in a single night. It is at this time that orchard-heating operations should be most carefully conducted. Apples and pears at this stage of development usually are not seriously injured by a temperature of 28-5° F. for thirty

minutes or less, provided the duration of temperatures below 32 0 F. does not exceed three hours. If the temperature drops to 29 0 F. only a short time before sunrise and has not been below 32 0 F. more than three hours, heating is unnecessary. However, if it appears that the lowest temperature during the night will be below 29 0 F., or if the. temperature falls below 32 0 F. more than three hours before sunrise, heaters should be lighted and the temperature maintained as near 31 °F. as possible throughout the remainder of the night. Small green apricots are extremely tender just after the shucks (dried calices') have dropped and before the pits have hardened. Apricots in this condition have been injured at longcontinued temperatures of 3i°F., and many growers think it necessary not to allow the temperature to fall below 32 0 F. as long as the pits are soft.

Different ' varieties of the same fruit often differ considerably in their susceptibility to frost damage. .The Delicious apple appears to be more tender than most other varieties of apples grown commercially on the Pacific Coast. The Bose pear is more susceptible to damage by frost than most other varieties of pears at similar stages of development, while the Winter Nelis is hardier than most varieties.

Frequency and Severity of Frosts.

Practically no scientific data are available as to the occurrences of frosts in Central Otago, but there is quite an appreciable amount of information of a practical nature. The main data from which these deductions are made are the temperatures taken by the Astronomical Society during 1922 and 1923 at Alexandra, Mr. H. E. Stevens from 1916 to 1921 at Clyde, and Mr. W. Bringans from 1919 to 1927 at Alexandra, and general talks with old-established growers. Although the information received from these sources cannot be wholly relied on, as temperatures have been taken in different situations and with nonstandard thermometers, it must not be forgotten that the matter of frost damage has always been of'vital interest to the fruitgrowers, and they naturally have a very good idea of what number of - degrees of frost recorded by their own instruments would injure their crops.

During the years 1916 to 1927 inclusive there appears to have been an average of under three frosts per year which might have done more or less injury. . From Mr. Bringans's records it would appear that his orchard ■ received a certain amount of injury (not always more than a heavy thinning) from two frosts per year over the last nine years. The largest numbers were in 1919 and 1920, when there were six and four frosts respectively. The most severe frost recorded was one of 9 0 , which occurred in both 1919 and 1926, the temperature being observed by mean's of a thermometer placed on the ground in an exposed position. It would therefore be fairly safe to assume that the average is very little more than two frosts per annum for which heating will be required. For the longest frost experienced last season one and three-quarters hours' burning would have been sufficient for protection. To be on the safe side, therefore, and to allow for false starts, my estimates are based on an annual average of three heatings of two hours each.

Losses and Character of Injury.

Losses from frost damage are injurious to the whole community as well as to the fruitgrower and his industry. The grower is injured through lack- of income, and his general inability to give his orchard that care and attention which is necessary whether there is a crop or not. This was very noticeable in Central Otago as a result of the 1926

frosts, when spraying, irrigation, cultivation, - and other essential work was neglected. Moreover, the orchardist has all his overhead expenses, such as interest or rent, to pay, and the damage occurs after his pruning and ploughing have been completed, much of his spraying done, and most of his supplies ordered for the season. The Government suffers through the lesser tonnage carried on the railways, and the smaller amounts collected in income-tax and Customs duty. The industry generally receives a set-back through high' prices forcing consumers to turn to other products, the lack of continuity of supplies being an important factor in the marketing of any commodity.

Sufficient details are not available to gauge the actual loss through frost sustained by growers in this district, but some idea may be gained by a comparison of the railway returns kindly supplied by Mr. C. Ashley, Stationmaster, Alexandra. The total weight of fruit railed from the railway-stations from Cromwell to Lauder on the Otago Central line for the years ended 31st March, 1926 and 1927 respectively, was 3,584! tons and 2,6i6J tons, showing a decrease of 968 tons in the year of the severe frosts. ' This weight approximately equals 45,000 bushels. The following are the amounts of fruit (practically all stonefruit) railed from Alexandra in the years 1921 to 1928 during the months of January and February, together with comments on the amount of frosting experienced : —

The total loss estimated by the local fruitgrowers’ association as a result of the 1926 frosts was £25,000 to £30,000probably a conservative estimate. Although the - losses at times have been heavy the district, apart from frosts, is so eminently suited to stone-fruits that growers who had been established for any length of time were quite well able to weather the storm. Moreover, it must be remembered that as one swallow does not make a summer, neither does one frosty .season mean a failure, or greatly depreciate the many natural advantages possessed by Central Otago as a stone-fruit-growing area. The alarmist reports broadcast over the country have often been greatly exaggerated to the detriment of the industry.

There are also frost losses of a different character to be taken into account, such as malformations which make only second-grade fruit. Some varieties of apples and pears show an ugly russeting around the eye, while some pears, such as Williams Bon Chretien, develop a wide russet ring around : the fruit. Another injury noticeable, especially on Cleopatra apples (Fig. 14) is the formation of small depressions or dents on the surface of the fruit which have the appearance of bitter-pit. When the skin is peeled there is nothing apparent but a slightly darker

green appearance. If cut a little deeper a corky layer is reached, and below this again is a distinct hole which has evidently healed over and does not appear to have any detrimental effect on the keeping-qualities of the fruit.

- Mr. J. R. Laing has noticed that “ strong-growing trees of any variety stand the frost better, and carry heavy crops while the weaker trees among - them are almost barren. Jonathan, Sturmer, and Cox, if they are frosted at the blossom stage and are heavily spurred all over, will throw out fresh blossoms and bear fair crops. •Delicious and Cleopatra do not possess the recuperative powers of the others. Apples have, so to speak, five lives : when properly set they have five pips. Should they all be frosted but one there is a chance 'of the apple growing, although it will be badly shaped. Good apples may be grown with only two, three, or four pips; the difference is that . they are . flatter in shape and have not the substance of a perfect apple.”

It was very noticeable during the season 1926-27 that pears, particularly Winter Cole and Winter Nelis, were dropping for no apparent reason at different times when they had nearly reached full size. Upon being cut, invariably the seeds were affected ; one, two, or at most three of the seeds on' one side would be fullgrown and. plump, the rest being shrivelled; moreover, in spite of light crops, these varieties did not size up as was naturally expected.

Will Frost-prevention Pay?

The individual grower is the only one who can finally answer this question. There appears to me to be three factors which should guide growers in this district in their decisions : (1) Is sufficient damage being done by frost to warrant the expense of protection ? (2) Do damaging frosts occur so frequently that the cost

of protection would be - too high ? (3) Is the orchard sufficiently remunerative, irrespective of frost, to protect ? There are orchards here that would not pay to protect' from any of these • points of view. Those orchards situated in favoured positions/ such- as the Clyde-Cromwell gorge, are frosted so seldom that the expense is certainly not warranted. Again, there are parts of the district ’ with orchards in which, I am afraid, protection would be too costly, on account of the too frequent occurrence of damaging frosts. Then there are orchards that are not producing sufficiently large crops to warrant the additional expense, and which, until they can be brought into better profit, must be allowed to suffer occasional damage, for the cost of protection can easily be greater than the net profit on the crop saved.

There will always be failures on the part of those who do not exercise sufficient care and forethought, and there will always be a number who will not undertake protection against frost in any form. . Therefore, for the successful frost-fighter there will be the higher price for his product in the years when frost takes toll of his neighbours' crops. , In this district, with its dry autumn, the buds ripen to perfection, with the result apparently that, barring frosts, a full crop is assured each year almost invariably. Thus, with the frost bogy out of the way growers can with confidence apply manures and other assistance to their trees, with the almost sure knowledge that they are fertilizing a crop, instead of the present uncertainty. In the United States there is an annual increase in the acreage under protection from frost, and I feel that the same will be the case here. This conjecture is strengthened by the opinion of Dr. Kidson, as expressed to the fruitgrowers, that “it seems probable that frost - protection by artificial heating will be a paying proposition for many growers in Central Otago. ,J Community Organization. Quite a considerable amount of co-operation is already being carried out by the fruitgrowers through their association in the purchase of equipment and fuel, and this has proved very beneficial, for such items as firepots become much cheaper when bought, in large quantities. It seems probable that financial assistance can also be arranged to cover the initial costs of installing frost-fighting equipment through the intermediate rural credit system. There are other avenues for co-operation, as, for example, in the matter of several adjoining growers on the one telephone combining to purchase one alarm between them. This would be placed in the coldest of these orchards, a fact which would have been previously ascertained by taking a series of temperatures. Members of the group could then help each other in lighting and managing the fires.

•In view of the probable early establishment of a climatological station at Alexandra, and subsequently, it is hoped, the stationing of a scientific investigator here, considerable assistance should be available in forecasting frosts and the amount of heating required to combat them.

(To be continued.)

—- 13th Sept. ' 14th Sept. 15th Sept. 16th Sept. Minimum at top of hollow 27-0 46-0 43-8 37Minimum 15 ft. down 25-5 44-0 41-0 35-5 Minimum 33 ft. down 23-5 39-o 39-0 31-0

Table 9.

Kind of Fruit. Stage of Development. • Buds closed but F]lll m Small Green . showing Colour. ±5Joom - . Fruits. Full Bloom. Small Green Fruits. F. 0 F. 0 F. Apples . . .. 25 28 29 Peaches . . 25 26 29 Cherries - 25 28 3° Pears .. .. .. .. 25 28 30 Plums .. ' .. .. .. 25 28 3° Apricots .. . 25 28 31 Prunes . . .. .. 26 28 30 Almonds .. .. . . 26 27 30 Grapes . . .. .. 30 31 3i 3i

Temperatures endured for Thirty Minutes or Less (Sheltered Thermometers) by Deciduous Fruits in various Stages of Development.

Year. Tons. Remarks. . Year. Tons. Remarks. Remarks. 1921 . . 391 Considerable amount 1925 . . ' 862 j Some a.pricots frosted. Some apricots frosted. of frost. 1926 .. 736j A little frosting. A little frosting'. 1922 - . . . 744 Some frosting. 1927 .. 145 Very severe damage Very severe damage 1923 . . 946 Very little frosting. by frost. 1924 . . 938 No frosting. 1928 .. 885 A little frosting. A little frosting.

Table 10.