Grape Anthracnose, or Black-spot of the Vine

New Zealand Journal of Agriculture, Volume 61, Issue 5, 15 November 1940, Page 372

Grape Anthracnose, or Black-spot of the Vine

Viticulture

(.Continued from the October issue.") Control of Black-spot Fortunately, black-spot is of a fairly slow spreading nature compared with other vine fungi, such as powdery mildew and downy, mildew, and is therefore rather easier to treat and confine to certain areas. ■ Because of its over wintering habits it is more amenable to winter treatment. It is evident that the destruction of all hibernating forms will remove the cause of infection and prevent fresh outbreaks. Therefore, where black-spot has caused considerable trouble, winter treatment is definitely essential, hence the efficiency of the winter swab or spray. Prevention is better than cure, and authorities agree on the superiority of

preventative winter treatment over the summer or curative applications made while the vine is in growth. Spring or summer treatment is supplementary to the winter treatment, and in order to combat the disease the treatment must be twofold, and should consist of: (1) The winter swab or spray to destroy as far as possible the hibernating form of the fungus. (2) The spring and summer treatment with copper sulphate (blue- * stone) mixtures to prevent the spread of the disease, which would develop from any of the wintering forms which have escaped destruction by the swabbing or spraying in the dormant period.

The Winter Swab Both concentrated iron sulphate solution and 10 per cent, sulphuric acid are effectual destroyers of black spot in the dormant season. Both, however, have considerable disadvantages on their own, and a compromise by a combination of the two has been proved to be the most reliable. The standard winter treatment for black spot consists of a thorough swabbing or spraying of the vines with a mixture of sulphuric acid and sulphate of iron. The treatment is as follows: — (1) After pruning, all cuttings should be collected and burnt. (2) If time and labour permit, the vines may have the loose old bark removed and burnt. To leave it on the ground is worse than useless.

(3) Thorough swabbing or spraying with the solution. A reliable formula is as follows: Sulphate of iron 20 lb. Sulphuric acid 8 lb. Water 10 gallons. Preparation of Solution There are several methods of making the sulphate of iron-sulphuric acid solution, of which the following are the two most satisfactory methods: (1) Place the iron sulphate crystals in a wooden, earthenware or lead vessel, pour the sulphuric acid over them, add the water (preferably hot) and stir until dissolved. (2) Dissolve the sulphate of iron by suspending it overnight in a piece of hessian in the water. In the morning add the acid slowly. Care should be taken when making up the solution, as the contact of the acid and water causes considerable spurting, and unless care is taken and the liquids poured slowly the operator is liable to receive acid burns about .the body. Being very corrosive, the solution must not be placed in any vessels made of any other metal but lead; it can be conveniently handled in wooden vessels. Spraying in the Dormant Season If the disease has been particularly bad in the previous season two applications are desirable. When only one swabbing is given it should take place as near the bursting of the buds in spring as possible. Unfortunately, the date cannot be forecast correctly, as the seasons vary greatly from one year to another, and even vary considerably in different districts in the same year. It is important not to leave the application so late that injury may be done to the bursting buds. When two applications, are decided on the first should be given a month to five weeks before bud-burst, and should be followed by the second application as near to budburst as possible. One effect of the swab is to retard bud-burst, and in districts liable to late frost this is a distinct advantage. The appearance of the vines after treatment is curious, and to inexperienced growers somewhat alarming, as they are blackened and discoloured. No damage, however, need be feared, provided the buds have not begun to move at the time of application. Complete coverage is most important, both with the winter and the spring and summer treatments.

Methods of Applying The Swab For convenience the term “swab” is used for the winter treatment, although this can be and very often is applied by spray pump. Swabbing is usually applied by means of a brush. Because of the corrosive action of the solution, the brush selected must not have any metal in the binding, and brushes are procurable which are bound with string instead of wire. The method of applying the swab is of less importance than the thoroughness with which it is done. Every single portion of the vine must be well soaked; the old wood of the stems are just as important as the new rods or spurs. When swabbing by brush, the brush must be moved from the nose of the rods towards the ends so as to avoid breaking off the buds. If spraying is decided on, it , is necessary to use special lead-lined knapsacks, and nozzles must be made of lead or ebonite to withstand the corrosive action. If there is considerable acreage to cover and it is decided to spray, special spray outfits with capacities of up to 70 gallons and fitted with non-corrosive pumps and fittings are procurable. The spraying is cheaper and of more rapid application than the swab, although it is not considered to be as thorough. There is also considerable wastage of liquid when spraying. The quantity required to swab an acre of trellised vines is approximately 20 gallons using the swab, and 25 to 30 gallons if sprayed on. A late winter control measure which has proved effective in the Australian Commonwealth consists of a double

Methods of Applying

The Swab

For convenience the term “swab” is used for the winter treatment, although this can be and very often is

applied by spray pump. Swabbing is usually applied by means of a brush.

strength of Bordeaux mixture applied just as the buds are bursting. This spray can be made from 5 lb. bluestone, 5 lb. high-quality hydrated lime, and 10 gallons of water.

A winter control measure (recommended by the Plant Diseases Division, Department of Scientific and Industrial Research) consists of a spray with concentrated lime-sulphur mixtures to destroy, as far as possible, the hibernating form of the fungus. This lime-sulphur spray should be applied at the rate of 1-15 together with a reliable wetting agent to act as a penetrator.

Spring and Summer T reatment

Although winter treatment can be very effective, further spraying is necessary during the growing season, particularly if the season is at all wet. Because of the ability of black-spot to develop at low temperatures, the treatment must be started as soon after budburst as possible in order to coat the plant tissues with a protective film of copper spray solution.

Make an application of Bordeaux mixture just after the first bud-burst at a strength of 5-4-50, and again when the later buds are bursting apply at summer strength of 3-4-50. If weather conditions favour the disease, spray again before blossoming and again as soon as the fruit has set. Later applications are governed by weather conditions.

The summer spraying control of black-spot is equally effective in the control of downy mildew, and although downy mildew generally appears later in the season, it can be safely counted on as controlling two diseases with the one spray.

Instructions on how to make Bordeaux mixture were published in the Orchard Notes in the September issue of the “Journal.”

—B. W. LINDEMAN, Vine and Wine Instructor, Auckland.

Cool Storage Notes

Stacking the Fruit

"X Y THEN being stacked in cool W storage chambers, fruit should be made accessible for constant inspection to enable deterioration to be detected in time to save repacking and loss. The lay-out should provide for ample passage-ways and the method of stacking the fruit should make inspection of the stacks possible without undue inconvenience or increase in the cost of handling. (Continued on page 384.)