DISEASES IN PLANTATIONS OF EXOTIC TREES.

New Zealand Journal of Agriculture, Volume XVIII, Issue 1, 20 January 1919, Page 63

DISEASES IN PLANTATIONS OF EXOTIC TREES.

In his report on afforestation operations in the South Island, contained in the annual report of the Forestry Branch of the Lands Department, 1918, Mr. R. G. Robinson, Superintending Nurseryman for the South Island (since resigned), makes the following references to this important subject : —

It is obvious that with advancing age our plantations will require more intense watchfulness for early symptoms of fungus or insect disease, as in many cases remedial measures may be applied with successful results if undertaken at the right moment. The climatic conditions this season have evidently favoured the establishment and diffusion of fungus troubles. Although Betula alba (English birch) is not extensively used in our scheme beyond marginal planting, it is regrettable that this handsome tree has fallen a victim to the disorder — Melampsoridium betulinae— that causes much disfigurement to the foliage and hastens leaf-fail. The uredo-spores and teleuto-spores are produced on birch, • and the other stages on larch, which tree usually acts as intermediate host. The seedlings at Tapanui, on disclosing symptoms of the trouble, were immediately sprayed with a fungicide— mixture—but the difficulty in applying the spray evenly over, the affected surface discounted to some extent the effectiveness of the treatment. The birches will be kept under special observation, and reported upon when circumstances warrant. ' . ■

Another fungus , disease that threatens to be troublesome is Lophodermium — pine-needle —which affects Pinus radiala in both the young and advanced stages. So far only isolated cases of the fungus on our nurseries are known. From the third year onward the affection is noticeable on certain trees, although occupying situations generally regarded as favourable for pine-growing. The tree leaders. of affected trees appear to gradually decrease their annual vertical development, and lateral branches become comparatively bare. In view of the enthusiasm shown by experts generally towards and the projected increased planting of this fast-growing pine it would be wise to collect further evidence from districts where premature pine-decay has arisen from an unrecognized malady.

Each plantation contains a small area that is devoted to the production of Pinus austriaca. From the seed-bed stage these Austrian pines are attacked by the aphis, Chermes pini, and after eighteen years in permanent positions have failed to become free from the pest. Naturally progress is much interfered with, although more minute investigations disclose the fact that in humid situations, where treedevelopment is more rapid, the insects are not so numerically strong. In a great many instances, where the Austrian is used in admixture with one of the more healthful pines, early suppression of the infested tree may be looked for.

An interesting demonstration of the comparative resistance to the needle-shed-ding fungus of the European larch (Larix europaea) and the Japanese species (Larix leptolepis) is in evidence at Dusky Hill Plantation, where side by side may be seen the two species growing in precisely similar conditions. Trees of the European species under stress of a trying dry summer have been almost entirely defoliated, whilst the needles of their Japanese neighbours, even at this late date, are still hanging tenaciously to the twigs. The European larch, however, has proved so far to be a slightly faster grower, although there can be no doubt that it is more susceptible to the premature needle-shedding, and consequently more liable to decay before the millable stage has been attained.

Thanks are due to Mr. A. H. Cockayne, Biologist to the Department of Agriculture, for his cheerful co-operation in research matters.