THE GARDEN

Otago Daily Times, Issue 26606, 31 October 1947, Page 2

THE GARDEN

Contributed by D. TANNOCK, A.H.K.H.t.

DISEASES OF VEGETABLE CROPS A few weeks ago I dealt with some ol the more common and most troublesome of the insect pests, now I propose to dea; with the more common diseases which attack vegetable crops. Most attacks oi diseases are caused by microscopic fungus parasites, which are composed of veryfine threads invisible to the naked eye, and which penetrate into the plant cells and injure or destroy them. Some of the threads come to the surface and produce bodies called spores, which are equivalent to seeds in the higher plants. These spores are blown or washed about, thus alighting on healthy plants, on which they germinate and cause infection with the disease This happens especially when moist conditions are present. Besides the myriads of spores used to spread infection in the growing season, most diseasecausing fungi also form special resting spores which survive the winter, to start the disease the next season. It is commonly said that prevention is better than cure, and this depends, m a garden, on the following practices: Good cultivation both before the sowing or planting of the crops to secure suitable drainage, and a suitable tilth, and after, during growth by frequent hoeing or forking, the application of suitable manures, and also the rotation of crops Excessive applications of manures often cause rank and soft growth, which is very susceptible to attacks of disease. The selection of disease-resisting varieties, and clean healthy seeds and seedlngs, is also important, as well as the early thinning of crops, so that the plants may get fresh air and light and room to develop, reasonable shelter from cold winds not a stagnant atmosphere); the emova and destruction of weeds, and the removal of all diseased vegetation and rubbish which would provide re. ratine? snores. Diseased plants when move! should not be put on the compost bean or be dug in, but should be burned at once. It is also advisable to anticipate attacks of disease in certain plants and to carry out a system of spraying beforehand. REMEDIAL MEASURES Remedial measures alter the disease appears, including the removal of infected ssr-cTW'jsffi dusts are chemical . substances used checking the attacks of disease fungi and so preventing their spread. The sp y nnri dusts when properly applied, w 'p h ro.S « SM'yeilS gSS, S“ V ‘Sd W bSUr“ r ‘“WIU whfcl? Sui’coSS “e foliage as completely as possible with a thin layer of the fluid; this prevents infection by the fungus spores. It is important to use a suitable apparatus and for the small garden a good or a bucket pump is quite satisfactory. N f h n Tus? b^ emphasised? however, that spraying and dusting cannot be. and Should not be relied on as remedies for ah “roubles, but should regarded simply as occasional aids to g° od cuUivat on The first line of defence must be skilful Ind sound methods of cultivation, such as good drainage, effectwe PTOaration of the soil, and a supply of materials win heln the plants to resist the attacKs of disease organisms. Some compost enthusiasts maintain that spraying is not necessary when suitable cornposts a healthy condition of the soil Is maintained, but, unfortunately, Ideal . conditions are not vet maintained in all gardens, and we have to reckon with the neglected and "diseased and pest-infested garden spreading trouble.

potato Blight

I will deal with the diseases of the potato first, for it is the most important of the food crops, and the on ewecould least do without. Early potatoes are usually dug before, the blight appears and, therefore, it is only the second earlies and main-crop varieties that need be considered. Preventive spraying is valuable, and the first application should be given before the first .earthing up. again before the second earthing and the final earthings. h In wet, muggy weather it may be necessary to spray every two or three weeks until the tops ripen off completely. The blight shows first as brown patches, which increase rapidly in wet weather, and the stems and leaves then become blackened and rotten. The spores, wh'cn are liberated in great quantities, wash down into the soil and soon infect the tubers, which show a brownish-red discoloration on and under the skin. Such tubers are worthless for keeping, and should not be stored. In addition to spraying, earthing up deeply and forming a sharp ridge on the drills help in preventing the spores from reaching the tubers. If the crop is nearly mature the tops can be cut or pulled off and burnt, and infected tubers should not be left lying about. The spraying materials recommended are either Bordeaux or Burgundy mixtures, which can be pre pared or bought ready for mixing with W Wart disease, which often appears in old cultivated gardens, can be prevented by lining the drills (when taken out) with either straw or pine needles, which prevent the young tubers from coming into contact with the soil. PARSNIPS AND CARROTS Parsnips on a whole are remarkably free from disease, the most troublesome being canker or rust, when the root is affected on the upper part or shoulders by a large wounded area which vanes in colour from reddish-brown to black. When this area is examined many bacteria and fungi are found to be living in the damaged tissues, but these are not considered to be primarily the cause of the trouble. Cracking of the roots, like cracking of the carrots, is encouraged by wet conditions following a period of dry weather, when growth was checked Modern varieties of both parsnips and carrots are bred to .have a small core, surrounded by much fleshy-tissue, so that the bulky soft tissues of cetain varieties are more readily affected by dry weather, followed bv rain, which makes them swell rapidly. Excess of manure, too early sowing, absence of sufficient lime and potash, and faulty preparation of the ground are all contributing factors. Splitting of carrots and canker in parsnips are classed as non-parasitic diseases. There are a number of parasitic diseases which attack carrots, but they are mainly storage troubles. RUST ON BROAD BEANS This appears on the foliage as whitish spots which soon burst, and are at first pale brown; later in the season they are dark brown, and are seen on the stem as well. Generally this disease is not serious but sometimes the foliage is so brown with the rust, that the hands and clothes that touch the plants will show a deposit of snuff-like brown powder. It is generally considered that when the attack is severe there is something wrong with the nutrition of the plants, and a deficiency of potash is the probable explanation. Other diseases which attack the broad bean, but are not serious, are leaf spot, non-flowering, and chocolate spot, all of which may be due to excessive manuring or lack of potash. CELERY DISEASES Leaf spot, known as blight, is caused by the attack of a fungus and is probably the most serious disease with which celery 'growers have to contend. The first signs are small scattered brown spot 3, which increase in size, and develop pin point-sized black dots. In damp conditions the spread is rapid; the brown or black areas also appear on the stems, and the leaves may be killed. As the fungus is carried by the seed, it is necessary to obtain disease-free seed, or to treat it with weak formalin, one part in 300 parts water, for three hours, wth occasional stirring, say. every half-hour. After steeping, the seeds are spread on blotting pap'er to dry before sowing. After the plants are put out, on the first signs of disease spray with Bordeaux mixture. Celery heart rot is caused by bacteria and is usually most severe in wet weather. The symptoms are that the centre of'the plant contracts a wet brownish rot and soon turns into a slimy brown mass ruining it. It is considered that this organism requires a wound through which to enter the tissue, and slugs may be responsible for this. It is important to keep the celery as free from these pests as possible, and dusting with lime and soot is often recommended. DUNEDIN GARDENING CLUB At the most recent meeting of the Gardening Club Mr R. Balch, the assistant superintendent of reserves, gave an instructive talk on the use of glass in the home garden. He first described the various typs of greenhouses, and their construction. and the . uses to which they can be put, such as growing grapes, tomatoes, flowers, early vegetables, and bringing on plants for both the vegetable and the flower garden. He also described the garden frame, mentioning its uses for bringing on seedlings and hardening them off. Cloches and their use in the garden, and their construction were described. He' also exhibited specimens of potting and seed sowing soils, seed pans, and pots. The next talk will be given by Miss Gretchen Williams on the propagation of plants.