Note 106 — Chapter III · THE VITICULTURE OF NEW YORK
Reading edition
Black-rot (Guignardia bidwellii (Ell.) V. & R.) usually appears first on the leaves where it forms circular, reddish-brown spots on which black pimples, or spore cases, develop. Within these spore cases, at maturity, are the summer spores. These are distributed by the elements to the growing parts of the plant and form new centers of infection. The diseased berries show analogous circular spots bearing spores and as the disease progresses the grapes wither, turn black, and become hard and shrivelled, sometimes clinging to the vine until the following spring. Growing shoots are attacked as well as leaves and fruit. During the winter and spring the resting spores are formed, usually upon the shrivelled berries.
Treatment consists of destroying as far as possible all diseased fruit, old leaves and prunings and in spraying thoroughly with bordeaux mixture as follows:—
1. Just as the pink tips of the first leaves appear.
2. From ten days to two weeks after the first spraying.
3. Just after the blossoming.
4. From ten to fourteen days after the third spraying.
5. After an interval of from ten to fourteen days from the fourth spraying.