ORCHARD PESTS.

Otago Witness, Issue 3061, 13 November 1912, Page 12

ORCHARD PESTS.

OUTBREAK IN CENTRAL OTAGO.

QUESTION OF IDENTIFICATION

Mr E. Oswald Reilly, who has paid more than average attention to the growing of fruit in the Otago Centra) districts, has just returned from a trip through the gold fields, and was waited on on the sth by a Times reporter to get his views on the out • break of disease which has occurred in some of the orchards in that locality. Mr Reilly said he had formed his own idea of what the disease which was affecting the peach trees really was, but - that his opinion was open to correction by the Government experts when they had examined the parts of the affected trees and the soil in which they had been grown, which had been forwarded to Wellington. Mr Reilly stated that ho considered the outbreak amongst the peach trees was really caused by the disease called peach curl, and that in the case of the young apricots these were dying as the result of an attack of “ die back.'’ He said peach curl was very prevalent in some of the orchards, though on the other hand a number of orchards had entirely escaped from any attacks. Taking the whole of the peach trees —old and young —in the orchards in Roxburgh, Dumbarton, Ettrick, Alexandra, Clyde, and Lowburn, Mr Reilly said he considered that peach curl was this year more in evidence than he had ever seen it previously. Borne of the districts were particularly clear of disease, while in others 75 per cent, of the trees were affected. “ Dio back,” however, was more pronounced in the young apricots. Mr Reilly said he could hardly believe that there was anything in the theory that the soils of the orchards had bgcome contaminated, in that some trees growing in the same ground might present a very healthy appearance, while others close by had died out. Wo append herewith a leaflet for gardeners and fruitgrowers on peach curl, blister, leaf curl, or Trenching (Kxoascus deformans) issued by Mr T. W. Kirk, Go vernment biologist;

“ This disease attacks various stone fruits, but especially the peach The peculiar ourlcd or blistered appearance which the young leaves of poach trees frequently present in spring is caused by a microscopic fungus which attacks their tissues. The blisters sometimes extend across a leaf, sometimes along it. The entire leaf may be so puckered up as to be unrecognisable, or only a portion may be attacked. The foliage becomes leathery, the blisters assuming various colours, from the normal green to red, purple, or white, or combinations of these. The foliage generally falls off, and another crop is thrown out; thus the tree is exhausted, and the yield of fruit greatly lessened and deteriorated,, or in severe attacks completely lost, because it usually falls a few weeks after setting. Tho attacks are worse .in damp draughty situations and in changeable weather. Thodiseaso lives through the winter on tho buds and in the wood; thus scions and buds from a diseased tree will carry the disorder into localities where it was previously unknown. Treatment: Nursery stock is frequently very badly affected, therefore take cure that tho young trees are obtained from a reliable firm. Bo most particular to avoid scions or buds from any tree that lias had the least trace of tho disease within two years. Keep a sharp look-out, and directly the disease appears in a peach orchard give the tree the greatest attention and care; no trouble should bo spared at this stage. ‘A stitch in time saves nine.’ All primings and fallen leaves from diseased trees should bo r; bed up and burned, opt dally in nurseries. Bordeaux mixture, properly made and applied, will check the diseu.se. Soon after the leaves have fallen prune the tree and burn leaves and primings; then spray the tree with Bordeaux mixture, using the 10-10-40 formula; then again, j list as the. buds are swelling, spray with the same for uvula. In the spring, just after the petals' have dropped, a third spraying should he applied, this time using the 4-4-40 formula; or, if tho foliage appears to be very delicate, use a still weaker spray, such us the 4-4-50. Excellent results have attended the substitution of Jime-.salt-and-.sulpliur spray for tho winter dressings, and its use is to bo preferred if the trees are affected with scale.”

Mr J. C. Blackmore, ex-Government pomologist, who recently visited Central Otago, lia-s informed the Christchurch Star that, as. far as his observations went, there was no unknown insect or fungus pest present in any of the orchards. He, however, noticed the presence of green aphis to a slight extent, and the fungus disease known as peach curl; in fact, ho had never seen the latter disease so prevalent, even in several of the older orchards, let alone the orchards more recently planted. He directed the attention - of several of the older orchardists to tho fact, and inquired of them tho reason, and in reply was in-

formed that until the last three years limesulphur spraying had been in general use throughout the district as a winter and spring spray, followed later with a spray of Bordeaux mixture, with the result that green peach aphis was little in evidence, and fungus disease, including peach curl, was completely controlled, no matter whether the weather during spring was dry or wet. However, since the use of oil sprays had been so strongly advocated, lime-sulphur washes have not been so much used, nor oven Bordeaux mixture, or applied so early or persistently as formerly. Then again, when trees had been sprayed with oil washes it has been found that Bordeaux mixture did not adhere nearly as well to the trees’ as when sprayed with liime-suiphur, henoo the fungus disease known as peach curl had each year been increasing and had become far more prevalent. The present damp season has been very favourable to its rapid development, and if cold weather continues for a lengthened time some of the trees may become completely defoliated, but would recover to a great extent their usual healthy appearance as warm weather sots in. There is, however, nothing to fear from the disease known as peach curl if spraying with the right material is performed at the right time.

With reference to the statement that trees have succumbed to the disease, Mr Blackmore states that ho knows of no cause which would affect trees in such a manner except the presence of alkaline salts in the soil, which are present more or less in the soils of all and districts. Each salt has its influence on plant growth, hut in different degrees of intensity and in nature of action. The three principal injurious salts present in the soil of arid districts are carbonate of soda, common salt, and Glauber salt, together with more or less of sulphate of magnesia and lime, and nitrates of soda and magnesia. If any of these salts or combinations are present in excess the unusual rainfall which of late has taken place in the Central Otago district may have dissolved them, and m solution with water have passed downwards. As soon as the rain ceases the capillary upflow of the water brings the injurious salts to the surface of the soil, the water passes off by evaporation leaving behind whatever materials it has dissolved and brought up from the lower layers, and in this manner the injurious salts may have acted very energetically, and in a detrimental manner, even causing the death of young trees which were not too well established. But so far, although Mr Blackmore is well acquainted with the dry districts of Central Otago, he has not detected the presence of alkaline in excessive quantities, only in small spots of varying strength, and this is common in all dry districts and easily dealt wifh.