PLANT DISEASES

Manawatu Standard, Volume LVIII, Issue 54, 1 February 1938, Page 2

PLANT DISEASES

GROWTH IN DOMINION. CONCERN EXPRESSED. The increasing number of diseases which affect plants grown on a commercial basis in New Zealand were commented upon by Dr O. H. Cunningham, Director of the Plant Diseases Division, who was in Palmerston North yesterday. He said that in the past twelve months no fewer than seven new diseases had invaded the country and had secured a firm foothold, these being onion smut, maizehead smut, grease spot of passion fruit, tomato canker, citrus canker, citrus blast and lialo blight of oats. The first two were caused by fungi and the remainder by bacteria. Onion smut, Dr Cunningham said, was undoubtedly the most serious disease in the Dominion at the present time so far as onions were concerned. It completed destroyed the bulb and once it had been introduced into an area it persisted in the soil for several years, he added. Large areas in America had gone right out of onioin-growing because of this disease and it would be a savage blow at the industry in New Zealand if the disease made headway here. Treatment was so costly that it. would be uneconomic. The disease had been reported from Canterbury, which was tlie main onion-growing area for New Zealand, and the incidence of the disease was now being investigated by the Plant Research Bureau and the Department of Agriculture. PERSISTENCE IN SOIL. Specimens of maize-head smut had been forwarded by tlie instructor in agriculture from tile Gisborne area. The fungus attacked the cobs, converting them into a smutty, black mass which was worthless. This disease also persisted in tlie soil for many seasons, making control measures particularly difficult. Dr Cunningham stated that a survey was to be made shortly with the view of ascertaining the extent of the infection and the most practical method of control. Grease spot of passion fruit had apparently not been recorded elsewhere and so there was no literature on the disease, added Doctor Cunningham. It had made its appearance amongst the passion fruit vines at Keri Keri, Auckland and Tauranga, and had proved such a serious problem that in moist climates it had made passion fruit growing difficult and costly. Tomato canker, Dr Cunningham stated, was very common last year in glasshouses. It attacked the stems, causing wilt and the final loss of the plant. This disease was seed-carried and had played havoc in the United States of America. Citrus canker made its first appearance last May at Keri Keri, but had since been found in most of the citrusgrowing areas of the north. Every effort was being made to eradicate it, as it was the most serious disease the citrus industry had .yet to face. In other countries it had been controlled only by the eradication of entire orchards where it had made its appearance. Work in New Zealand, however, during the past season had given encouraging results. This had been in the nature of removing infected foliage, twigs and branches from trees.

Citrus blast was a' relatively serious disease in other countries, hut so far had not proved of very great economic significance in New Zealand. It attacked trees that had been weakened previously by frost or other agencies. Halo blight of oats had been found in one or two localities only, so far. It was a seed-borne organism which could readily become widespread and assume serious economic significance. Dr Cunningham pointed out that present _ knowledge suggested that all these diseases had been introduced into New Zealand with seed or on the host plant. Their presence in the Dominion also suggested that present methods of trying to exclude serious diseases of this nature were inadequate. He added that during the last four or five years the Plant Division had had to investigate several other diseases, all of which had increased production costs and some of which had rendered once profitable industries uneconomic. A ease in point was the advent, some eight years ago. of the grease spot disease of the Canadian \\ onder bean, which in a single season practically ruined a profitable seed industry in Marlborough and Canterbury.