BIENNIAL CROPPING OF APPLES.

New Zealand Journal of Agriculture, Volume 54, Issue 6, 21 June 1937, Page 349

BIENNIAL CROPPING OF APPLES.

R. G. Hamilton,

, Orchard Instructor, Hamilton

In the fruit industry to-day it is widely recognized that a high level in production is desirable. Furthermore, it is also realized that fluctuations in crop totals from year to year have a decided detrimental effect upon the stability of markets, and finally upon the grower’s net return. In consequence it is the endeavour of most orchardists to secure consistent rather than spasmodic crops. Biennial cropping, by which is meant the tendency of a fruit-tree to bear a heavy crop every alternate year and light crops in the intervening years, is probably the greatest factor against securing consistent crops. Many varieties of apples, principally those which are spur bearers, are affected by biennial cropping. This habit may first be brought about by any factor, natural or otherwise, which causes an exceptionally heavy crop in any year. Once the natural balance has become upset the cycle of biennial cropping quickly becomes established, and careful treatment is required to correct the trouble and again bring about average annual crops. To understand corrective treatment better a grasp of the causes, underlying the cycle of biennial crops is desirable. When the tree carries an exceptionally heavy crop, one which is beyond its normal capacity, the phenomenal demand made by the growing fruit seriously depletes the elaborated sap-supply, . and results in the semi-starvation of the developing fruit-buds. Consequent upon this semi-starvation, the majority of the fruit-buds remain undeveloped and fail to produce fruit the following season. During the season of the light crop the surplus of elaborated sap produces excessive bud-development, with a consequent heavy crop the following season, and so the cycle continues. The apparent limiting factor is that of elaborated sap. This may be caused by a lack of an adequate and available food-supply to the roots, or by insufficient leafage to elaborate the available sap, or by both of these. The spur-bearing varieties, apparently because of their sparse leafage, are more prone to be thrown out of balance by a heavy crop. In a previous article on this subject entitled " Biennial Bearing in Apple-trees ” (this Journal, Vol. 44, No. 17, pp. 38-41), the writer discussed methods of overcoming the biennial-cropping habit, and the following

observational experiment which was carried out amply supports the contention that this unfavourable aspect of fruitgrowing may be overcome. The observation was made possible by the ready co-operation of Mr. W. J. McMiken, of Hamilton, who carried out the suggested treatment in his orchard, and later adopted the practice generally on apple-trees in his orchard. The variety, Dunn’s Favourite, was selected for the purposes of the observational, test, because it is considered to be one of the varieties most prone to be thrown out of consistent cropping. The particular trees were planted in 1914, and were well grown, being approximately 12 ft. to 14 ft. high and having a 14 ft. spread. The average number of leaders on a tree was in the vicinity of twenty-four. At the commencement of the observations the trees were heavily laden with short fruit-spurs, while practically no lateral growth was to be found. The trees had a rather exhausted and stagnant appearance. Over the previous few years the crops were estimated by Mr. McMiken as being from 3 to 5 bushels in the “ light ” years and from 14 to 16 bushels in the “ heavy ” years. Annual manuring had been carried 'out, the trees receiving approximately 3 lb. of superphosphate and 2 lb. of bonedust each. Green manuring with blue lupins had also been commenced in 1928. The method of improvement was by (1) increased manuring, continued growing and ploughing under of green crops, and by (2) an improved system of pruning. In the winter of 1930 a heavy reduction was made in the number of spurs carried by the trees, approximately 50 per cent, being, cut away, and a commencement made in the reduction of the number of leaders by thinning out from three to four in each tree. The manuring was increased by 1 lb. of superphosphate per tree. The. following season was the “ light ” year, and a large amount of new lateral growth was produced. In the winter this new growth was left uncut, while a further inroad was made into the remaining old spurs', and approximately 20 per cent were removed. The leaders were reduced in most of the trees by a further two. The manuring was increased to 8 lb. per tree, comprising 6 lb. of superphosphate and 2 lb. of bonedust. The second season was due in the cycle as a “ heavy ” year. With the heavy thinning of the fruit-spurs, followed by a heavy thinning of the fruit, the crop was reduced and approximately only 10 bushels per tree were carried. Extensive new lateral growth was made, while a heavy development of fruit-buds took place on the previous year’s uncut laterals. At the winter pruning approximately 30 'per cent, of the remaining old spurs were cut away, and all new growth, except where crowding,' was left intact. The leaders were again slightly reduced in numbers. In the summer of 1933 the trees now presented quite a different appearance, being liberally furnished with new lateral growth. The development of healthy buds had been extensive, and the promise was for a heavy crop in what would, in the old cycle, have been a “ light ” year. In the manurial programme an increase to 10 lb. per tree was made, which, consisted of sulphate of ammonia .i| lb., superphosphate 61b., and bonedust 21 lb. -

The following season turned out. to be one of heavy crop, close on 20 bushels per tree being produced. The majority of the fruit was now being carried on the lateral wood. Despite the heavy crop new lateral growth was satisfactory. Since then, with the exception of one year when a late frost lowered the crop, cropping has been consistent, and this season sees the fourth consistent crop of over 20 bushels per tree. Each winter the pruning has been on the same basis, that of cutting away the old and exhausted wood, and leaving the new lateral growth to take its place in the sequence of fruiting. The provision of lateral growth has provided the tree with increased leafage, and the benefit is to be seen in the healthy rejuvenated appearance of the trees. The manuring has been gradually increased, sulphate of potash being added in 1934 and since. Carbonate of lime, 12 cwt. to the acre, was applied in June, 1935. Last year’s manuring consisted of 15 lb. per tree applied in August of a mixture containing fish manure, bonedust, and sulphate of potash at a ratio of 2-10-3, and in October with 4 lb. per tree of meat-meal. As a result of this season’s satisfactory crop, together with further satisfactory new lateral growth and good fruit-bud development, it is considered that these trees have now been established in consistent cropping. Other biennial cropping varieties in the same orchard appear to have responded in a like manner, and have reverted to annual average cropping. In orchard practice it must be recognized that increased quantities of manure at times must be applied if heavy crops, together with sufficient new growth, are to be maintained. Increased manuring, however, will not correct biennial cropping or maintain consistent crops unless it is associated with the correct pruning practice. Briefly put, this consists, in the case of all apple-trees, of the removal each winter of the older and more exhausted fruiting-wood, and the spacing and leaving unshortened of all one-year-old lateral growth.

At a large meeting of farmers at Rakaia in May a discussion took place regarding the growing of blue lupins for sheep-feed. There was great diversity of opinion, but the majority state that lupins were not good sheep-feed and that stock had to be starved before they would eat the lupins.— Fields Superintendent, Christchurch. Certified White Clover in Canterbury . —ln the Rangiora district the common method of establishing mother-seed white-clover areas is to broadcast 3 lb. to 41b. of seed on an autumn-sown wheat crop. The white clover is sown in the spring after the wheat has been rolled, and light harrows are used to cover the seed. Although this is natural white-clover country, some of the stands have been almost complete failures this year. . Heavy wheat crops have sometimes resulted in poor clover establishment. Rather than incur the expenses of preparing the land for spring sowing along with rye-grass, most farmers prefer to risk sowing the high-priced clover-seed with wheat. In one or two cases certified Hawke’s Bay rye-grass has been sown with the clover and certified seed of both plants harvested off the same area. Probably the reason for the popularity of sowing with wheat is the excellent manner in which red clover has at times been established. Red clover, however, is more suitable for this practice than white clover, as its upright habit enables it to withstand the shading better, and the deeper rooting-system of red clover enables it to withstand better a dry period, after the wheat has been removed and has left the land depleted of moisture. — Instructor in Agriculture, Christchurch.