PLANT DISEASES

New Zealand Times, Volume XXXII, Issue 7048, 9 February 1910, Page 8

PLANT DISEASES

ONION AND CABBAGE TROUBLES. A paragraph is going the rounds of the country press to the effect that blight has made its appearance in the onion crops in tho Wanganui district, the stalk being shrivelled up half way up the stem. In the Warrarapa it is stated that a blight has appeared in the cabbage crops. The root is attacked and the plant, instead of developing into a

cabbage, remains a sickly plant all tiio lime till it withers otf. OX LON .MILDEW.

There is little doubt that the trouble with the onions is onion. mildew, a fungus disca.so which periodically makes its appearance under favourable climatic conditions. In tho 1001-5 season it was rather bad. Growers should bo well acquainted with this trouble and the boat in on ns of dealing with it, a-s it was fully explained in the annual reports of the Department of Agriculture tor 1905 ami 1996. , . Al . Mr T. W. Kirk then explained that the trouble was a mar relation to the (1 muled potato blight. All members ot Die onion family, he says, are subject to attack, the leaves being the organs which aru directly affected. Tho first signs ot dic-oa.se consist of the development of yellow patches on tho leaves. These areas soon become covered with a delicate coating of mould, much as if they had been powdered with dour. Thiscoating soon changes to a grey or light brown colour. Meanwhile, the disease increases rapidly until the whole leaf is affected ami withers away. The appearance of thick heads, says Mr Kirk, is especially characteristic o-f the disease. The hulks' are. not directly attacked, but •if tho disease appears early in tho year they remain extremely small and do not mature properly, so that tho crop is practically There arc two methods of reproduction—first, by summer spores, which servo to disseminate the disease fre-m crop to crop during tho growing season, and, secondly, by •rounded, thick-coated bodies, called resting spores, which are produced in the decaying tissues of the 1 wives, and remain dormant throughout the winter. In the spring they germinate am] inoculate the young crop. The preventive treatment recommended is Bordeaux mixture, using the 4—4—40 formula. Messrs Johns Bros., of Auckland; wrote to Mr Kirk saying that by following his advice to spray with Bordeaux mixture they saved their whole crop. OLXTB-KOOT. The Wairarapa cabbage trouble ia doubtless “■club-root,” “ huger and.toe,” or “canker,” and, like onion mildew, has been fully described and dealt with by Air Kirk in reports and bulletins which could bo had for the asking. The trouble is dealt with in bulletin No. 11, and in tho annual report of tho department for 1005. Club-root is extremely infectious, and attacks almost any plant belonging to the natural order cruciferae, such as turnips, cabbages, rape, swedes, radishes, cauliflowers, etc. Infected young plants show thickenings and knot-lilco swellings on the roots. As the plants become older the swellings increase enormously and become very large, the club parts then turn brown and deoa-** the death of the plant ultimately resulting. The cause of the disease is a skitne fungus, so small as to bo imperceptible only under high magnification. The spores of this minute organism can remain in the soil for several years in a dormant condition, but when a suitable crop Is sown in the ground they germinate, and, entering the young, delicate roots, soon lead to the whole crop becoming affected. Apparently tho only preventive meaf?nre which can bo taken- against the disease is to heavily dre*s the land with lime, and to carry out a careful rotation of crops—grain of all kinds, mangolds, carrots, potatoes, etc., can be grown in infected land without danger. All diseased roots should be burnt.