FRUIT RESEARCH

Nelson Evening Mail, Volume LXXIII, 13 June 1939, Page 9

FRUIT RESEARCH

INTERNAL CORK IN APPLES AILMENTS OF STONE FRUITS INVESTIGATED BORON DEFICIENCIES As in former years considerable attention has been paid to investigations relating to the fruit industry (states the annual report of the Cawthron Institute). Work on the use of borax in controlling "internal cork” of apples and physiological ailments of apricots d other stone fruits has been actively prosecuted both in the Nelson district and in Central Otago. The manurial experiments at Upper Moutere and at the Annesbrook orchard have again ; emphasised the importance of a com- , plete manure for the nutrition of fruit , trees on many Nelson soils. ’ The Mycologist has continued work , on the identification of fungi associated with “mouldy core” and “eye-rot' o ' apples, while the Entomological Def nartment has completed initial studies • of the raspberry bud-moth and the raspberry saw-fly in relation to the i Nelson raspberry industry. A detailed ■ study of the life cycles of woolly aphis i and its parasite Aphelinus mali has ’ been commenced with a view to securt i n K a more complete control of woolly t aphis in the spring and early summer

BORON DEFICIENCY AILMENTS (1) Brown spotting of apricots and pitting of cherries. —In co-operation with the Department of Agriculture, investigations relating to the control of brown spotting of apricots, pitting of cherries and gumming of plums have been continued at Alexandra, Central Otago. In the case of apricots, definite control of the brown spotting ailment has been effected by the use of a 0.1 per cent, borax spray or of J-lb. borax applied as a topdressing around the tree in the spring. The control plots (without borax) gave only 2 per cent of healthy fruit, while the trees sprayed or topdressed with borax showed 94 to 98 per cent, of healthy fruit. Chemical analyses of apricot samples taken from the different plots gave confirmatory evidence of boron deficiency as the primary cause of ailment. In the control fruit the boron content was only 5.7 p.p.m. boron as against 34.5 p p.m. and 46.5 p.p.m. boron for the sprayed and topdressed trees* respectively.

In the case of cherries the field experiments during the past season did not show a clear-cut result as “pitting” did not develop on the control trees. Analytical data, however, definitely showed an association of low boron content with the incidence of pitting in other orchards.

(2) Internal cork of apples.—(a) Duration of effect of borax topdressings: During the past season the results of both field and chemical studies showed that Mb. borax per tree used as a topdressing gave commercial control of “internal cork” of apples for a period of at least three seasons. In certain cases, however, the boron content of both soils and fruit indicated that the supply of boron was being reduced to a low level. The experiments are being continued during the present season to ascertain the period over which a given dressing of borax controls “internal cork” ailment. ''b) Effect of borax sprays on foliage of apples.—ln view of reports that injury to foliage has occurred from the use of borax sprays in the control of “internal cork” of apples, further spray tests have been conducted with a wide range of spray combinations. In no case has any sign of damage to foliage or fruit been noticed in the tests. It would appear that borax sprays used at strengths of 0.20 per cent, and 0.10 per cent, are perfectly safe if care is exercised in the thorough mixing of the spray solution and if lime is used in coo'unclion with lead arsenate sprays.

(c) Effect of borax on the cool storage quality of apples.—ln previous reports mention has been made of the detrimental effect on the keeping quality of Jonathan apples, as a result of using topdressings of borax greater in amount than £-lb. per tree. The work has now been extended to other varieties of apples as indications are not lacking that different varieties of apples react in different ways to high boron content of the fruit.

Cool storage tests of Jonathan fruit from trees sprayed with borax at 0.20 and 0.10 per cent, strengths showed no reduction in keeping quality. If anything. the percentage of “internal breakdown” was slightly less on the sprayea plots than in the adjoining control trees without borax sprays. (3) Early Defoliation of Apple Trees. —During the past three seasons early defoliation of Jonathan trees on certain manurial blocks at Upper Moutere has occurred to an increasing extent. The defoliation commencing as it does before the end of December adversely affects the size and colour of the fruit and the formation of fruit buds for the next season’s crop At Upper Moutere the trouble is most severe where heavy potassic manuring has been employed in the treatmnet of the trees. Defoliation, however, is not wholly confined to trees treated with liberal amounts of potash, for a survey of orchards in different parts of the Moutere Hills and the Moutere Valley showed many trees affected to a greater or less extent. There can be no doubt, however, that the use of potassic manures increases the incidence and degree of defoliation.

The results of a large series of injection experiments and of chemical analyses of many leaf samples indicate that the actual cause of leaf defoliation is a deficiency of magnesium. The injection experiments have shown that magnesium salts control defoliation, while the leaf analyses confirm the re-

sults of the injection experiments in showing a very low magnesium status of the leaves of affected trees. Low figures for magnesia, however, are associated with high figures for potash. The role of potash in the production of defoliation requires further elucidation.

(4) Manurial Experiments.—The manurial experiments on Jonathans at Upper Moutere and of Sturmer and Dougherty apples at the Annesbrook orchard have been continued. The results in both orchards emphasise the importance of complete manures, containing nitrogen, potash and phosphate, for many Nelson soils. Spectacular results at Upper Moutere have followed the manuring of trees which have been untreated for 12 years. Neither phosphate and nitrogen nor potash and nitrogen gave such good results in growth, foliage development and fruit production as the complete manure.

(5) Apple Stock Experiments.— In the case of Cox’s Orange variety. Northern Spy stocks continue to show superiority over seedling stocks. Several Cox's Orange trees on the latter stock are now badly affected with “sour sap.” but in the case of trees on Northern Spy stock no detrimental effects are observable. Jonathan and Sturmer varieties,

however, have given better results with Double Vigour and Seedling stocks than is the case with Northern Spy stocks. (6) Pruning Trials.—An opportunity was taken to test what is known locally as the Hawkes Bay system of growing fruit trees. In this system main leaders are reduced to three or fout and no pruning other than the cutting out of interlocking growth is attempted. Both Cox’s Orange and Jonathan trees were tested under this system of management. but the results showed that these methods were unsatisfactory roi Nelson conditions. Growth in the case of the Jonathan variety was outstandingly weak and gave little promise for future fruit production. (7) A very good season was experienced at the orchard. Little trouble was occasioned by fungus disease and insect pests. Fruit production was heavy on all varieties of apples and pears. The commercial crop from 8$ acres of bearing orchard amounted to 5200 cases of fruit, of which 4570 cases were of export quality.

The following table shows the quantity of different varieties exported and the prices realised in England :

EXPORT FRUIT Price per case N.Z. currency. No. Cases. Variety. Shillings. 260 Cox's Orange n.B 450 Jonathan io.l 50 Delicious 10.4 712 Lord Wolseley 10.1 771 Sturmer 9.8 949 Dougherty 12.4 955 Winter Cole Pears 9.1 (8) Fungus Diseases.—Mouldy-core and Eye-rot: The identification of fungi commonly present in the diseased flesh of apples affected with “mouldy-core” and “eye-rot” has been continued. The relative percentages of the different fungi nave been assessed. The data are now being tabulated and a summary of the results is being prepared for publication. General.—The usual notification service ii} connection with the maturity of “brown-rot” and “black-spot” ascospores has been maintained for the benefit of orchardists in the Nelson district.