Apricot Culture

New Zealand Journal of Agriculture, Volume 84, Issue 4, 15 April 1952, Page 325

Apricot Culture

MONG the numerous kinds of fruit which can be grown successfully in New Zealand the apricot (Prunus armeniaca) ranks high in popularity. It is discriminating as to climatic and soil conditions, and these factors, together with other aspects of its culture, are discussed by J. Coombe, Orchard Instructor, Department of Agriculture, Roxburgh, in this article, which will be concluded in the May issue of the "Journal". THE apricot is one of the most useful hardy fruits in that it can be used as a fresh fruit, for jam making, or preserved or dried for winter use. At one time it was thought to be a native of Armenia, but further study suggests that its native habitat was farther east in western China, and some strains known as Russian apricots appear to have come from Siberia. The Chinese are reputed to have cultivated apricots 3000 years B.C. W. H. Chandler states that the apricot was introduced from Italy into England in the 13th century, and was grown in Virginia as early as 1720. The first trees in New

Zealand were imported from Australia in the early 1860’s and planted at Clyde, Central Otago. More trees were imported a year later, and these were planted at Coal Creek, Roxburgh. Central Otago is still the main apricot growing centre in New Zealand, there being about 93,400 trees in that district at 31 March 1951 and 26,100 trees in the remainder of the fruit growing areas of New Zealand. Location Apricot trees favour a locality with a wide variation between summer and winter temperatures, and for this reason Central Otago, with its sharp dry cold in winter and hot dry summers, is ideal for them. Districts subject to humid conditions during spring and early summer are not suited for apricot growing, as brown rot. develops rapidly. An

attack of this disease during blossoming can cause a serious loss of potential crop. A site that is reasonably well sheltered from the south and has a northerly aspect is preferable to one with a southerly aspect. Apricots come into blossom early in spring (early September in a normal season), and from this period until the fruit has developed to the size of a walnut they are very susceptible to damage by frost. In the dormant stage the flower buds of most varieties are as resistant to cold as peach buds, but they swell more quickly when warm day temperatures are experienced and are therefore more subject to damage during frosty nights. Unless a grower is prepared to provide protection, or to risk frequent loss of crop, localities subject to spring frosts should be avoided.

Soil Although apricots are propagated on various types of root stocks, apricot, peach, and plum, which make them suitable for varying soil types, they prefer deep, loamy, well-drained land. They will not tolerate a heavy, retentive subsoil, as they very quickly succumb to “wet feet”. In Central Otago the best-quality fruit is produced from trees growing in schist rock soils, particularly those which contain a reasonable amount of weathered rock. In soils of this type the trees produce good crops over a long period of years. Some trees are stated to be from 75 to 80 years old and are still in a good, vigorous condition and bearing heavy crops.

Drainage If the drainage is not adequate, it should be attended to before planting is started. Like the roots of most other fruit trees those of apricots will penetrate to a good depth if the soil is suitable; it is the drainage of the subsoil, where the deep roots are, that is so important. Because water is not seen lying on the surface of the soil, it does not mean that it is well drained. In some soils surface water is rarely seen, yet the soil is waterlogged a few inches below the surface. The fertility and physical condition of a waterlogged soil deteriorate rapidly and much more cultivation is required to break it down to a good tilth. The depth and distance apart at which drains are laid are governed by the outlet and the type of soil. Tile, brush, or stone drains are efficient if properly constructed; if they are placed 4ft. deep and a chain apart, adequate drainage should result on free-draining loamy soils. In heavier soils, drains must be shallower and closer together. Land which cannot be drained readily should not be used for apricot growing.

Irrigation

The importance of irrigation in districts of low rainfall cannot be stressed too strongly. If soil moisture is insufficient while the crop is growing, individual fruits will be small and inclined to be tough and dry; during pronounced drought conditions fruit will sometimes wither on the trees. Tree growth, fruit bud development, and storage of food in the tree parts also suffer if there is a continued lack of soil moisture throughout the summer, giving the tree a check from which it may take a year or two to recover.

If soil moisture is lacking, water should be applied shortly after fruit set, and again after the stone has hardened; irrigation should be avoided when the stone is hardening, as fruit drop may result.

After the crop is harvested irrigation is often neglected, but at this stage when the buds for the following season’s crop are maturing and the tree is building up food reserves, a plentiful supply of moisture is necessary. However, trees should not be irrigated too late in the season, as this tends to retard ripening of the fruit buds and young growths, making them more subject to low-temperature injury in winter. When irrigation has to be resorted to sufficient water must be supplied to reach the rooting system if good results are to be achieved. In most instances water is led down small furrows from the main irrigation channel and then allowed to spread out over the soil. A departure from the use of furrows is irrigation through sprinkler systems, though very little is known at present as to whether this method will be likely to create conditions more favourable for the development of disease. Shelter Shelter from strong winds does not appear to be quite as important for apricots as it is for some other kinds of fruit. Many successful growers have very few or no shelter trees round their orchards. If the locality is exposed to very strong winds, some shelter should be provided, but a block of apricots should not be so hemmed in that no wind can penetrate, as it is likely to make conditions worse for the development of brown rot. Further, if the orchard is on a slope and in an area subject to frosts, a shelter belt on the low side increases

the frost risk by holding up natural air drainage. Where protection from strong winds is essential Lombardy poplar or one of the Pinus species can be recommended as quick-growing trees suitable for the type of shelter needed. p llVA 4.; rtn Although clean cultivation is recommended for apricot growing, it does not mean that no weeds should be allowed to grow. The land should be broken down to a reasonable tilth in early spring just before bud movement and left undisturbed until after

the frost risk period, has passed. A cover crop or heavy weed growth at this period increases the risk of having the crop frosted. Throughout the summer light, shallow cultivation should be carried out to keep down excessive weed growth, which robs the trees of soil moisture. About mid-January a cover crop should be sown to assist in keeping the organic content of the soil at a high level. Oats,, barley, ryecorn, and blue lupins are all useful plants as cover crops. Seed is sown at the rate of lg to 2 bushels per acre. In sowing the cover crop it is advisable to apply 2cwt. of superphosphate mix per acre to assist it to become established as rapidly, as possible. In low-rainfall districts, such as Central Otago, the growing of cover crops can rob the fruit trees of essential moisture if adequate irrigation is not available. Many growers are now using straw or hay spread over the soil in late spring at approximately one bale per tree to maintain the humus content of the soil under these conditions. This material is well rotted down by the following spring, when it is worked into the soil. This strawing down is also beneficial in areas where cover crops cannot be grown successfully. Cover crops or mulches should be incorporated in the soil sufficiently early for them to have rotted completely before bud movement of the trees begins. When such material is breaking down it tends to cause a temporary shortage of available nitrogen in the soil. If a cover crop must be turned in at this stage, when nitrogen, starvation would be detrimental to the trees, a quickly available nitrogenous fertiliser, such as sulphate of ammonia, should be broadcast to maintain the nitrogen supply. Soils of a fairly heavy type should be ploughed up to the trees on both sides in autumn and left in the rough through winter, when the action of frosts will assist greatly in making them easier to work. On heavy soils the run-off of surface water is greatly facilitated if a deep furrow is left in the centre of each row after ploughing. Manuring The quantity and quality of fruit produced from an orchard depend largely on the fertility of the soil and its management, and through the judicious use of fertilisers a high level of soil fertility can be maintained. No definite recommendations can be made as to the quantity of any particular fertiliser that should be applied to orchard trees; the fertility of the soil and the vigour of the trees, which vary considerably, determine the amount and kind of fertiliser required to ensure maximum production.

If any one of the three main elements, nitrogen, phosphorus, or potassium, is in very short supply, this deficiency will show in the foliage; therefore the condition of the tree is the best guide as to what fertiliser should be used.

Nitrogen promotes strong _ wood growth, larger foliage, and assists in the setting of fruit. The tree’s requirement of nitrogen is greatest in the early part of the growing season, and it is usually at this period that it is in short supply, particularly if a green crop or straw, has been incorporated

in the soil and is in an unrotted condition. An excess of nitrogen is liable to cause soft, sappy growth and make the tree more susceptible to an attack of disease. The fruit is also. inclined to be soft and loses much of its keeping quality. A deficiency of nitrogen causes the foliage to change to a yellowish green and may produce such symptoms as stunted growth, small leaves, poor fruit set, or early defoliation. ic v P rv readilv leached Nitrogen is very readily leac e SnJlUr? in late winter or very early applied m late winter or very ea_ y in spring, ,so that it is available to tne tree 3 weeks before blossoming. Nitrogen applied so that it becomes available to the tree only in the later part of the season tends to delay fruit maturity. , . . .• ■ , , 4-u „ Phosphates assist plant growth, particularly in the early stages, by stimulating root activity. They are a ot connected with fruit bud development and fruit maturity. A deficiency o phosphate causes poor root action and a dull green and bronzed appearance of the older leaves. Potash , improves plant fibre and builds up resistance to disease, It counteracts the effects of excess nitrogen and improves the colour ana keeping quality of the fruit. Potash is essential for the production of carbohydrates such as starch ana sugar. The foliage of trees starved of potash is dull green. Leaf scorch and early defoliation are further symptoms of a lack of this mineral. Nitrogen, phosphorus, and potassium are all essential for the development and health of the tree and fruit;'therefore a complete fertiliser which contains these three elements is much

better than a manure which contains only one or even two ox them. phosphates and potash are taken up by trees in greater portions during the early stages of development in spring, They also take some time before they become available to the trees, which g>rtes it necessary to apply them betore s P rm ® S™ Degins, a number of fertilisers can be used f o supply the ■ three main elements required. Sulphate of ammonia, superphosphate mix, and sulphate of potash are those usually app ii e d to orchard trees to furnish nitrogen, phosphoric acid, and potash. Blood and bone is i liq .p d to a °reat extent The main point to consider in the purchase and use of fertilisers is the percentage of suitable plant constituents in them, Quantities applied per tree must be varied, using the appearance of the individual tree as an indicator of its requirements, bearing in mind not only the crop to be m atured in the current season, but also the encouragement o growth for provision of future fruiting wood. For some trees 41b. would be sufficient, while others may require up to 121 b. to maintain them in good condition. Liming: Lime supplies the element ca i c i um which is necessary for tree g row th. It improves the texture of heavy so ils, thus making them easier wor v and reduces or neutralises SO II acidity. The reduction of soil ac j dy encourages the growth of b ene fl c i a i so organisms. Most New Zealand soils are somewhat acid and can be a pplied with safety, but in Central Otago the position is reversed. Most of the orchard soils there are inclined to be alkaline or have an excess of lime. The addition of lime to an alkaline soil increases the alkalinity and also tends to make

other elements such as manganese, boron, and iron unavailable to the tree, thereby causing deficiency troubles. In general, district practice for a particular soil type may be followed, and a great deal can be learned from a study of the results of past applications, but unless the soil is tested for acidity and calcium content, it is not possible to be definite on how much lime, if any, should be applied. Frost Fighting As the apricot tree is one of the first to blossom in spring, it is more subject to frost damage than other fruits. Because of this frost risk fire-pots have been installed in many orchards and frost fighting has become a recognised part of apricot culture, particularly in Central Otago. However, orchard management can assist to some extent in decreasing the first risk at this period, as experimental work has shown that over a clean cultivated soil there can be up to 5 degrees less frost than over one which is carrying a cover crop or weed growth. Two types of fire-pots are in general use, both of them made of metal and consisting of three parts, container, “spider”, and lid. The smaller pot holds 10 pints of fuel oil and burns from 2-g to 4 hours without refuelling. The burning time depends on whether the spider is taken off or left on. Spiders are taken off to increase heat only when the temperature continues to drop after all pots have been lit. The larger pot holds 21 pints of fuel oil and will burn for as long as 10 hours, which obviates the necessity for refuelling during the night.

Just before the danger period, which in an early season begins during late August, the pots are placed in the orchard in the centre of each row and filled in readiness for lighting. Usually one pot is required to each tree. Some growers place two small pots side by side to avoid refuelling during a burn, and the second pot is lit when the fuel in the first is almost exhausted.

The alarm thermometer which is used to warn the grower of a dangerous fall in temperature is placed in an open position in the orchard or close by the grower’s residence. It is connected to batteries in the alarm box, thus forming a circuit, and when the temperature drops below a certain point the circuit is broken and the bell rings continuously inside the residence until it is switched off. The thermometer is set a degree or two higher than the danger point to enable the grower to collect staff and begin lighting the pots before damage occurs.

Other thermometers are placed in various positions throughout the orchard, usually one to about every 3 acres of trees, which allows the grower to check up on any variations in temperature. Sometimes variations of 2 to 3 degrees F. take place in very short distances, so that it is necessary to try to locate cold spots and place thermometers there. The thermometers are placed about 4ft. 6in. high under covers on posts in open positions. False temperatures will probably be recorded if they are placed in trees or in positions which are too sheltered. The delicate nature of these thermometers makes it essential that they are not breathed on or touched while being read, as this is likely to lead to a false reading.

Lighting should be started first where the temperature is lowest and on the side the air drift is coming from. Each pot in the outside row should be lit, but it is wise to light only alternate pots in every second row for a start. If the temperature still falls, the alternate pots in the rows which were left during the first lighting should be lit. By lighting only sufficient pots to keep the temperature above the danger point, fuel is saved, and if the frost is not a severe one but of long duration, the alternate full pots can then be lit when the first ones have burnt out, thus obviating the necessity of refuelling at night. Once burning has started it is necessary to make frequent rounds of the thermometers to check the temperatures. The torches for lighting the fire-pots are filled with a mixture of equal parts of kerosene and benzine, and left in readiness. The wick and gauze in the spout should be examined and renewed if necessary, and the torch tested before it is required. On no account should a torch be used unless the gauze is in good condition and in place, as it is this part which prevents the lighting mixture in the torch exploding. , Frequently trouble is experienced in lighting new pots for the first time, but this can be overcome by adjusting the torch wick so that more lighting fluid runs out on to the fuel oil.

There are two main methods of refuelling the fire-pots. One method •is with the use of a portable spray outfit with the pressure reduced to a few pounds per square inch. Too much pressure will cause the oil to overflow the sides of the pot before it is properly filled. The other method is with the use of a portable tank- to which a hose is connected at the lowest point, and the oil is gravityfed into the pot. A special filling gun is procurable for filling the pots by either of these methods. To prevent possible damage to trees from fuel oil deposits spray tanks and pumps used should be thoroughly cleaned, preferably with a caustic solution, and then rinsed well with clean water before spraying fruit • trees. When fire-pots are removed from the orchard after the frost danger period has ended they should be stacked on the headlands after the surplus oil has been emptied into convenient vats or drums for future use. Pots should not be up-ended and placed in the forks of trees, as the drainage from them has been known to kill trees. The provisional list of temperatures dangerous to apricot production in Otago was compiled by the Fruit Research Station of the Department of Scientific and Industrial Research at Earnscleugh and was published for the guidance of growers. Experimental work on these lines is still proceeding.

PROVISIONAL LIST OF TEMPERATURES DANGEROUS TO APRICOTS IN OTAGO Temperatures (degrees F.) at which injury may occur if maintained 30 Stage of growth minutes or more Roxburgh Moorpark Red Pink .. .. .. 23 White tip . . , • • 24 Full bloom . . .. 27 28 Petal fall (stamens green) .., ..28 29 Stamens withered .. 29 . 30 Burst calyx .. .. 30 . 30 Green fruit (.3in. to ' ,sin. diameter) .. 30 . . 30 Green fruit (,7in. to lin. diameter) .. 29 29

Dry flowers or fruit may withstand the temperatures listed for considerably more than 30 minutes, but if the temperature . falls 1 degree F. or more below the figures shown for any given stage of growth, extensive damage may occur in a short time; Ten _to 15 minutes at 1 degree below the dangerous temperature is likely to cause a substantial loss. When flowers or fruit are wet from rain, damaging- points are approximately 1 degree F. higher than those shown. It appears that damage is far more extensive and is more rapid when the trees are wet. Dampness from light dew or fog does not seem to have the effect given by drops of water left by rain. It is possible that temperatures higher than those listed might cause injury if continued long enough. Thus at the burst calyx stage 31 degrees F. maintained for several hours might cause damage. Experimental evidence is not yet available on this point, but it is not likely to arise often in practice, as temperatures fluctuate considerably during most frosty nights. When comparing this list with field results it should be remembered that the temperatures quoted were recorded close to flowers or fruit, and not at 4ft. 6in. above ground level. Varieties Of the considerable number of varieties of apricots, only a few are grown to any extent in New Zealand. The main ones are as follows: Newcastle: The best early variety; fruit small to medium, roundish to slightly elongated; flesh orange yellow; pink blush on cheeks of exposed fruits.

Oullin’s Early: Fruit medium to large, roundish, with flat top; flesh golden yellow; slightly pink cheek; inclined to be soft, and does not carry well.

Dundonald: Medium-sized fruit; rich golden yellow flesh which ripens from the inside; carries reasonably well; similar in shape to Roxburgh Red.

Roxburgh Red: Large elongated flatfish fruit; golden flesh, red cheeked; good keeper and carries well; fruit is inclined to shed right up to maturity.

Early Moorpark: Similar to Moorpark but earlier.

Moorpark: The best dual-purpose apricot; fruit medium to large, roundish, slightly elongated, with deep yellow flesh; skin deep yellow

with a red blush; keeps and carries well; a heavy bearer.

Bolton: Fruit medium to large, roundish, elongated; flesh orange yellow; a good carrier and heavy cropper, but fruit subject to cracking and brown rot. Trevatt: A good dual-purpose apricot. Fruit medium to large, elongated, inclined to be flat; yellow fleshed; carries well; bears heavy crops. Royal Late: Fruit small to medium; blushed cheek, deep yellow flesh; a good keeper and carries well. The varieties have been listed in the approximate order in which the fruit reaches maturity. Harvesting dates have been omitted owing to variation from district to district. In genera], harvesting is started during December ■ and continues until late February. Apricots are self-fertile and therefore do not require other varieties for cross-pollinating purposes. Root Stocks Apricots can be secured on three root stocks, apricot, plum, or peach. Those contemplating planting apricots should procure root stocks suitable for their particular soil'type. For light well -drained soils, peach stocks may be successful. In a good loamy soil with adequate drainage, apricot stocks are better, though on the heavier soils or where the soil is inclined to be more retentive of moisture plum stocks may do better. Planting Land to be used for fruit trees should be put into the best possible condition long before it is planted. Any serious weeds such as couch grass or convolvulus should be eradicated, as once they get among the rooting system of a tree they are almost impossible to clean out. Apricots in the main develop into large trees, and do better if they have adequate space. In the past trees in many of the established orchards were planted too close to get the best return from them. Close planting hampers cultural operations, the trees have a tendency to grow higher, and only a small percentage of the crop is borne on the lower portions where it is easier and cheaper to thin and harvest. On good fertile land trees should be planted 20 to 24ft. apart both ways.

The best time of year to plant varies with the • district and soil type. On light well-drained soils autumn planting is quite satisfactory, but on heavy soils or those inclined to retain moisture the trees should be left heeled in until spring. Autumn planting is not recommended for districts subject to very severe frosts.

A beneficial practice, common in Central Otago orchards, is to plant the young trees out in a nursery block for the first year. Usually when the trees arrive from the North Island or Australian nurseries the roots have been cut back very severely, and unless the trees receive the best of attention many are lost, particularly

in a drought season. By placing them in a nursery for the first year, they generally receive much better attention, especially in regard to irrigation.

Marking out the positions for the trees should be completed over the whole area before the holes are dug. The pegs used for marking the exact positions of the trees have to be removed when the holes are dug, but by using a planting board and extra pegs, this difficulty may be overcome. The planting board is made from a piece of lin. timber 4ft. 6in. long and 6in. wide by cutting V notches in both ends and in the centre of one side, the centre one being cut a little more than half-way through, about 3-gin. deep. The board is placed so that the peg marking the tree position is in the centre notch, and pegs are placed in the end notches and driven securely into the ground. The board and centre peg are then removed, leaving ample room to dig the hole. Trees can then be correctly sited by replacing the board on the end pegs and placing the trunk in the centre notch.

In digging the hole, it is best to discard the subsoil and use good topsoil in the bottom. ■ When the hole is finished it should be large enough to take the roots comfortably without cramping, the bottom being left dome shaped to facilitate root spread. Up to Jib. of fertiliser mixed with the soil will assist the tree in getting a good start, but care should be taken that it does not come in direct contact with the roots. A mixture of 2 parts (by weight) of blood and bone to 1 part of serpentine superphosphate mix will be found satisfactory.

Young trees should be left in the nursery or heeled in until the holes are ready. Roots of young trees should be examined before trees are placed in their permanent positions and bruised or damaged portions pruned off. Very few trees have roots evenly spaced round them; usually most of the roots or the strongest of them are to one side. These stronger roots can be made to assist the tree to stand up to strong winds or help it if it is being planted on a hillside by placing them in the direction from which the prevailing wind comes, or, in the case of slopes, pointing uphill. The balance of the roots should be spaced as evenly as possible round the hole.

The tree should be planted as deep or a little deeper than it was in the nursery, but not to such a depth that the bud union is covered; the soil mark on the trunk will indicate the depth at which the tree • was growing in the nursery.

In filling in holes use good topsoil from the sides of holes. When the roots are well covered give the tree a slight shaking up and down until the soil has worked in among them. At this stage the soil -should be well firmed by treading. The last of the soil used for filling in should be left loose and a little above the usual ground level to allow for settling down.

It is unwise to prune the tops of young trees before planting, as the buds to which they are pruned may get damaged during handling and planting. This frequently spoils the shape of the tree.