_General Notes._--The downy mildew is a fungus known botanically as
_Peronospora viticola_. Its native country is the United States, but its
greatest damage is done in Europe. It appears as white, downy spots on
the underside of the grape leaves, which are gradually destroyed, and
later on attacks the berries, which shrivel and spoil. In California the
downy mildew occurs frequently on wild native grapevines, but only very
rarely on the cultivated Asiatic vines. Dr. H. W. Harkness, the eminent
mycologist, found it only once on cultivated vines in the Sacramento
river bottom. These vines were growing close to native vines, from which
the fungus had spread. There is no fear that this fungus will ever
spread and cause damage in our State as long as the vineyards are given
plenty of air. In France the _Peronospora_ has caused much damage, but
is now being combated with bluestone and lime solutions, according to
the following formula: Slake thirty pounds of lime in seven and a half
gallons of water, also mix sixteen pounds of bluestone (copper sulphate)
in twenty-five gallons of water. Mix the two together, and either
sprinkle the foliage with it, or dilute it further with say five
hundred gallons of water and spray the vine leaves on both the upper and
lower sides. According to Dr. Harkness the efficiency of this spray
cannot always be relied on. So far no other fungi have appeared in the
raisin districts of this State, nor have we reason to fear that any will
attack the vines.
[Illustration: Downy Mildew (_Peronospora_), Greatly Magnified. _a._ The
Fungus Growing out of a Stoma of the Vine Leaf. _b._ Transversal Section
of Vine Leaf, showing Fungi and their Tuberous Mycelium.]