Zinc Deficiency of Newcastle Apricots

New Zealand Journal of Agriculture, Volume 99, Issue 6, 15 December 1959, Page 585

Zinc Deficiency of Newcastle Apricots

Horticultural Research

D and stone fruits are both affected by zinc I deficiency in certain parts of the Alexandra district. The most susceptible apricot variety appears to be Newcastle, but all the varieties commonly grown can be affected. In this article W. S. Kemp, Horticultural Instructor, Department of Agriculture, Alexandra, reports on a zinc deficiency trial carried out on a block of young Newcastle apricots growing in the Clyde-Cromwell Gorge.

IN 1953 after a lead given through a series of tree injections carried out in the Alexandra district by W. B. Healy, Soil Bureau, trials in collaboration with E. G. Bollard, Fruit Research Station, were laid down in various orchards. These have since demonstrated the importance of zinc deficiency in pip and stone fruits in certain parts of the Alexandra district. An account by E. G. Bollard of some of this work has been published in the “Orchardist”. In the trial on the block of young Newcastle apricots growing in the Clyde - Cromwell Gorge, symptoms were first noticed during the 1952 season, when the trees were three years old. The trouble was confined to a portion of the block sited on a small fan laid down within fairly recent years from a wash on the side of the gorge. The soil was light, containing a large percentage of broken schist, and was subsequently found to have a pH of 8.2.

Symptoms were principally a mild leaf chlorosis, with a lighter interveinal colour very similar to that of manganese deficiency from which it was difficult to distinguish.

Others had typical resetting and little leaf symptoms together with leaf chlorosis. There was a strong tendency for new shoots to develop laterals from the leaf axils when the second growth cycle began in summer, giving a feathery or “witch’s broom” effect. Leaves were smaller and harsher looking, buds were more prominent, and in the more severely affected trees growth was considerably reduced.

In February 1953 after the grower had applied to separate parts of the block sprays of zinc sulphate plus hydrated lime and manganese sulphate plus hydrated lime there appeared to be some reduction in the chlorotic effect on the foliage where zinc sulphate had been applied. A further zinc sulphate spray was applied later in autumn over the whole block. During the following season symptoms were very mild, being confined to those trees which had shown severe symptoms the previous season.

In the spring of 1954-55 leaf symptoms began to appear quite early, and indications were that the incidence would again be fairly severe. Trials were laid down using sprays of zinc, manganese, and chelated iron, both alone and in various combinations,, to test the possibility of a combination deficiency.

Two applications were made, in February 1955 and November 1955. No response was obtained and later it was found that the material used as zinc sulphate was not true to label; consequently in February 1956 a further series of treatments was applied. At that stage the foliage on all trees showed a marked reduction in chlorotic effect as compared with the spring, probably due to seasonal fluctuation and varying weather.

In the spring of 1956, while chlorosis was evident on some trees, there was no sign of it on any of the trees receiving zinc either alone or in combination with manganese or iron. By February 1957, though slight leaf symptoms had begun to show in odd leaves of the zinc-treated trees, the incidence was much reduced in comparison with that on other treatments, and growth in previously severely affected trees which had received zinc was considerably improved.

This was considered sufficient evidence to assume that the chlorosis was due to . a zinc deficiency and this diagnosis has been borne out by the fact that foliage chlorosis has been almost entirely eliminated by the grower applying annual sprays of zinc sulphate since, and growth on previously severely affected trees has become normal.

Toward the close of this trial the trees had begun to crop and it was apparent that zinc deficiency also affected cropping ability. Severely affected trees carried very few fruits, and what fruit was produced was much smaller than normal. This tendency has also been observed on apricots which have shown zinc deficiency symptoms on other properties in the district.

From this and other trials, as well as results obtained since by various growers, it is apparent that, particularly on light sandy soils or where the soil tends to be fairly alkaline in reaction, zinc deficiency can affect both tree growth and cropping.

On these soils zinc sulphate plus hydrated lime (bordeaux formula, 6-8-100) applied annually as a foliage spray either in late spring or early autumn will assist in correcting any deficiency and promote better growth and cropping. Application of zinc sulphate alone at 25 to 50 lb per 100 gallons during the dormant season is also effective.