VEGETABLE DISEASES

Wairarapa Times-Age, 11 August 1939, Page 3

VEGETABLE DISEASES

METHODS OF CONTROL. Of all the vegetable diseases which trouble the gardener, one of the commonest, and at the same time most destructive, is that known as finger-and-toe, or clubroot. Almost every species of the cabbage family is susceptible to this disease, not only those kinds commonly grown as vegetables, but also the ornamental forms, such as stocks and wallflowers, and even related weeds. As its alternative name implies, finger-and-toe is a disease of the root, and, in fact, it is always confined to those parts of the plant, where it produces irregular swellings, very variable in size and shape. These swellings, if the attack be a mild one, may be confined largely to the lateral roots, coverting them into distorted fingerlike processes, but which are insufficient to do more than impede the normal development of the plant. Generally, however, the effect is much more extensive. Few, if any, fibrous roots are developed, and the whole root system becomes converted into one swollen mass, which may even protrude above the surface of the soil. Plants thus, affected can usually be recognised by their flagging, unhealthy leaves and stunted growth. Clubroot and Acid Soil. The great trouble is that the reproductive spores can be dormant in the soil for many years, thus serving to carry the infection to the next susceptible crop which is grown upon that land. It is a matter of common knowledge that crops grown on acid soils are particularly subject to finger-and-toe. In such soils the parasite is able to flourish best, but, if the soil is rendered alkaline, its development is checked and may even be inhibited. It is for this reason that the use of lime has long been regarded as one of the best means of checking finger-and-toe disease. At the same time, it must be remembered that the beneficial effects of liming in this-con-nection will only become fully apparent when it has resulted in the actual neutralisation of the acidity of the soil. Before this can happen, it is often necessary to apply quantities of lime considerably in excess of what would be demanded by the crop under normal conditions, and, in addition, a considerable time must elapse before such dressings can operate satisfactorily. Some more immediate remedy thus becomes necessary, and can be found in the use of chemical substances. Mercuric chloride, or corrosive sublimate, as it is often called, is effective, but. unfortunately, this is very poisonous, and for this reason it is made difficult by the authorities for the general public to obtain supplies. In the hands of any reasonably careful and intelligent person, however, such risk should be more imaginary than real, and certainly no greater than that attendant upon the use of poisonous weedkillers and many other chemicals, which are often handled with but only too little caution.

A “one in two thousand” 0.05 per cent solution is prepared by dissolving one ounce of the chemical first *bf all in a small quantity of hot water, and then diluting this to 124 gallons by the addition of cold water. The holes for the plants, which should preferably be made with a dibber, are then filled in twice with the above solution just before setting the plants themselves. For this purpose about half a pint of the liquid will be required for each plant. All things considered, it is wiser and more convenient for the amateur gardener to rely upon one of the proprietary clubroot deterrents prepared by horticultural chemists, and sold in containers carrying instructions for use. The foregoing instructions refer to the planting of healthy seedlings in infected soil, and, since the treatment is a preventive and not a cure, for the disease, it is absolutely essential that the plants set should be quite free from even the slightest sign of clubbing. Since such healthy seedlings cannot always be readily obtained in the market, and no clean soil may be available for a seed bed, it may be necessary to raise them upon infected land. This can usually be done quite satisfactorily by treating the seed bed itself and the young plants when removed, with the antidote. Jhe seed should be sown in drills, and preferably in a frame. Immediately before sowing, each drill should be watered with the appropriate solution already referred to. Later, when the young plants are some two inches high, or about four weeks after they first appear, the solution should be applied to the soil between the drills. We have also found it to be reasonably effectual in securing disease-free seedlings to sow the seeds and transplant in a very limy soil. Almost any quantity can be added to the seed bed, etc, but one pound to the square yard will, be a good guide. Another point is to transplant the seedlings early, thus encouraging a free-rooting system, which will help the plant wonderfully in contrast to the one long tap root often only present. Common Scab of Potatoes. Another general trouble for the vegetable grower is common scab of potatoes. Happily, this disease does no seriously affect the tuber under the skin, but it does spoil the potatoes, so far as cooking and serving them in their jackets is concerned. Here, however, acid soils render infaction less probable. Corrective measures are thus advisable where soil is very alkaline. A reliable preventive measure is to immerse the dormant planting sets. before sprouting or planting, in a formalin solution. Mix half a pint of commercial formalin in 15 gallons of water. Put the potatoes in a canvas bag, and immerse in this liquid for two hours. Spread the tubers out to dry immediately after withdrawal. and before planting.