Feb 28 2009
Pest and Diseases of Grapes
The strong-growing varieties can be grown as cordons if the site is warm and the soil good. The rows have to be 6 feet apart and the cordons 10 feet apart in the rows. The cordons are trained horizontally and thus stakes and wiring must be provided. Under this system a stake with a minimum diameter of 3 inches, and preferably chestnut, should, when 2 feet of its base has been thoroughly treated with Cuprinol, be driven into the ground securely so that the top is 2 feet 3 inches above soil level.
They could also be grown on the ‘Grow as you like’ system, being allowed to scramble over a trellis or cover a fence or wall. Under this system very little pruning is necessary, though it does pay to cut back the fruiting laterals in the summer at two leaves above a bunch.
The leaves of the vines grown against walls are often attacked by Red Spiders, and the answer here is to syringe the under surface of the foliage in the evening, twice a week, from the beginning of June onwards. In cases of bad attack some liquid derris should be added to the water.
Once in position the rod is cut back, by about a quarter, and then the shoot which develops from the end bud is tied along the bottom wire until it reaches the next cordon where it is pruned, in the summer, to just above a bud. The laterals or side growths that develop from the lower parts of the cane are tied to the top wire when they are long enough and they are then pruned.
Powdery Mildew causes white patches to appear on the leaves and then the fruit, then the young shoots. Individual grapes that are attacked will either fall or go rotten. Vines that are mulched are seldom attacked with mildew, and when the young laterals are properly spaced out, so that they are not overcrowded, this disease seldom appears. Dusting the plants with a fine sulphur dust largely cures the trouble when seen.
This method is not suitable for varieties producing very thin canes or for those which bear the best fruit at the end of very long canes.
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