H.—34.

have been issued at each visit. From observations to date there is fairly clear-cut evidence that the type of turf most suited to aerodromes which are required to stand hard wear is that class of turf most closely approaching a playing green or lawn. The pasture species such as rye-grass and white clover are definitely unsuited to hard regular wear. Some rather drastic treatments will be necessary to convert the pasture type of turf to a good hard-wearing mat. Some considerable expenditure will also be necessary to control white clover which up to now has been fairly well established, but is already provitig to be quite dangerous. Supplies of grass-seed suitable for aerodromes have been secured, the main species needed for this work being Chewing's fescue, certified brown-top, Poa pratensis, and yarrow. In addition, according to soil type and climate, there is need for some creeping-bent seed and dryland brown-top seed. At one particular aerodrome-site Puccinellia was sown, and a further quantity of this seed is to be sown this autumn. Due primarily to the unusually dry season, there has been little success so far from spring sowings. From a grassland point of view, and particularly in so far as ecology is concerned, this aerodrome turf work is very interesting and enlightening. The aerodromes are situated from the far North to Invercargill and from altitudes just above sea-level to some two or three thousand feet. Climatic factors are extremely variable. Rainfall and temperatures are two very important factors governing the grassrgrowth, and these seem to be of as much importance as does soil type. The soils vary from practically pure sand to gumland clay, volcanic loams, pumice ash, peaty soils, and reclaimed salt-marsh country. Numerous photographs illustrating the turf work for aerodromes are, by permission, being secured, and these permanent photographic records will be of great assistance in the future not only for aerodrome work, but in connection with grassland research in general. Most of the travelling between aerodromes has been done by aeroplane, and particularly good opportunities of studying the various classes of country and the vegetation types thereon have been afforded. In addition to turf problems, such major works as reclamation of land on sea-mud flats, the stabilizing of sand, the consolidation of peaty soils, and the better drainage of heavy clays are being studied. Several important factors have been observed, and these are closely associated with the greenkeeping research work of former years. For example, high-fertility soils are not necessary, acid soils of low fertility are usually more suitable to the development of good tough turf. The tcrrific amount of wear-and-tear of aerodromes, particularly at the training-stations, necessitates a very tough, hard-wearing turf. Some difficulty was experienced in securing satisfactory machinery for the distribution of seed and manure, but the position is now fairly satisfactory in view of some recent improvements to New-Zealand-made machines. Greenkeeping Research. This work has been continued, and during the year the work has been reviewed and published. The Annual Greenkeeper's Conference was again held, and Diploma Examination conducted. Lectures and Demonstrations. Assistance has been given to young farmers' clubs and other organizations in the matter of lectures and demonstrations to visitors to the area have been made. Publications. The following papers have been published by members of the staff during the year : — Gorman, L. W. (1940) : " Perennial Rye-grass," N.Z. Jour. Sci. & Tech., 21, 345a-347a. — (1940): " Blind Seed Disease Investigations." N.Z. Jour. Sci. & Tech., 22, 79a-83a. Corkill, L. (1940) : " Cyanogenesis in White Clover I." N.Z. Jour. Sci. & Tech., 22, 65b-67b. PLANT DISEASES DIVISION, OWAIRAKA, AUCKLAND. Director : Dr. G. H. Cunningham. For the purposes of continuity, an outline of the work is presented in the form followed in previous years, investigations being grouped under five main headings : — (i) Diseases of Plants ; (ii) Plant-protection ; (iii) Timber-preservation ; (iv) Pomology ; (v) Miscellaneous. I. Plant Diseases Investigations. General. Several new diseases were identified during the year, those of economic importance being Bacterial-spot of Plums (Bacterium pruni). —Found on several varieties of Japanese plums in Hawke's Bay ; probably introduced from the United States of America, where it is a serious disease of plums, peaches, and apricots. Virus of Beet (Beta Virus 2 of Smith). —Isolated from sugar-beet and mangels in the Manawatu. Elsewhere a serious disease of these hosts, and likely to prove so in the Dominion. Virus of Rhubarb. —Identity not yet established. Forwarded this year from Canterbury, where it is said to have been prevalent for ten years or more. A survey showed that upwards of 75 per cent, of the plants in established beds were infected, about one-third of these being killed outright. Unless immediate remedial measures are applied, it will destroy the profitable rhubarb industry of Canterbury.

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