mummied grapes and
the leaves and prunings of infected vines as soon as possible is
apparent. This treatment, however, is not sufficient, and the disease
can be effectually controlled only by thorough spraying with bordeaux
mixture (4-4-50). The first application should be made just before the
grape blossoms; the second, shortly after blossoming. The amount of
material applied matters less than evenness in distribution and
fineness of the spray as applied. In rainy seasons, perhaps a third or
a fourth application should be made in regions where the disease is
serious; the third is made when the berries are the size of a pea; the
fourth, as the berries become large enough to touch each other.

_Downy-mildew._

Downy-mildew (_Plasmopara viticola_) rivals black-rot for first place
among fungous diseases of the grape. It is found in all grape regions
east of the Rocky Mountains but does most harm in northern localities.
Like black-rot, downy-mildew attacks all the tender growing parts of
the vine, but is chiefly found on the foliage and is usually less
destructive than black-rot. As first seen on the foliage, the work of
the fungus appears as greenish-yellow, irregular spots upon the upper
surface which later become reddish-brown. At the same time on the
under surface of the leaf, a thin, white downy growth puts forth. The
spores of the fungus are produced on this downy growth, and under
favorable conditions are distributed by wind and water to all tender
parts of the vine, where they germinate and begin their work of
destruction. The fruit is attacked when partly grown, as shown in Fig.
45, becoming covered with the gray down of the fungus, the "gray-rot"
of the grape-grower. If the berries escape the disease until half
grown, the fungus causes a brownish-purple spot that soon covers the
whole grape, giving the disease at this stage the name of "brown-rot."
Besides the summer-spores, another form of reproductive bodies is
produced in the winter to carry the fungus through the resting period.

[Illustration: FIG. 45. Grapes attacked by downy-mildew.]

Downy-mildew, like black-rot, spreads most rapidly and does most
injury in hot, wet weather. As with practically all diseases of the
grape, much can be accomplished in the way of control of the disease
by destroying infested leaves, shoots and berries which contain the
winter spores, but these sanitary measures are not sufficiently
effective and vineyards must be sprayed a