1124 
disturbed. This stage of the disease is 
sometimes called “brown rot.” 
Besides the summer spores mentioned, 
there is also produced within the dis- 
eased tissues another form of reproduc- 
tive body, sometimes called a winter, or 
resting spore. These spores are produced 
in much smaller numbers than the sum- 
mer spores and are provided with a 
rather thick, dark-colored outer covering 
apparently intended for their protection 
during the winter. 
This disease, like the black rot and 
many others, develops most rapidly and 
does most injury during hot, wet weather 
Treatment 
It is desirable to destroy aS many as 
possible of the diseased leaves, shoots, 
and berries, which may contain the 
winter spores. Thorough spraying, as 
recommended for the black rot, will ef: 
fectually control this disease 
References 
United States Department of Agricul- 
ture Farmers’ Bulletin 284. 
Connecticut Experiment Station Bul- 
letin 56. 
Lirtte Lear, See Miscellaneous Dis- 
eases, this section. 
Powdery Mildew 
Uncinula spirahs 
The only important fungous disease 
that is of special interest to grape grow- 
ers in the Northwest at the present time 
is the disease known as the powdery 
mildew. This is most serious on the 
European varieties and consequently is of 
special interest in California and those 
sections where these varieties are grown. 
Symptoms 
The disease may attack any herbace- 
ous part of the vine. On the leaves the 
fungus appears in the form of white or 
greenish-white patches of mildew These 
may run together till the greater part 
of the leaf is covered. The fungus may 
also attack the young canes, beginning 
at the base in the form of small patches; 
or in severe cases the whole surface may 
be covered. The green or white mildew 
is easily rubbed off, leaving on the canes 
brownish spots which soon turn black. 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
If severely attacked the canes fail to 
grow or mature properly. When the dis- 
ease attacks the blossoms they fail to 
set. If the young fruit is attacked when 
quite small the berries may drop off. If 
attacked when half grown they develop 
irregularly and the affected parts become 
hardened, the ripe berries becoming ir- 
regular in form. If severely affected they 
may crack, thus becoming useless for 
table or market use. If this cracking ig 
early they may still be used for wine, 
though in moist seasons they may be at- 
tacked by various molds. The berries 
are usually not attacked alter they be- 
gin to ripen. When only slightly af- 
fected the berries may ripen without 
cracking, but are disfigured by spots or 
blotches which reduce their value for 
market purposes. 
Cause 
The cause is a fungus known technical- 
ly as Unewnula spiralis. This, like all 
fungi commonly Known as powdery mil- 
dews, grows more or less superficially on 
the surface of the affected parts. The 
fine thread-like mycelium is largely ex- 
ternal, sending short feeding branches 
into the epidermal cells of the host. 
From this superficial mycelium erect 
branches are formed which break down 
into short cells or spores. When abun- 
dant these give the spots the powdery 
appearance that accounts for the popu- 
lar name of this and other related forms. 
These spores are spread by the wind and 
thus may come to rest on a healthy part 
of a vine. They germinate by putting 
out a thread of mycelium which branches 
and attaches itself to the surface of the 
host and grows into a fungous plant 
which, when it has reached its full de- 
velopment, produces spores in countless 
numbers like that from which it grew. 
This stage, which is known as the sum- 
mer spore stage, serves to spread the 
fungus rapidly. 
Later in the season another form of 
the fungus, sometimes spoken of as the 
winter or resting stage, is produced. This 
form gives rise to spores borne in tiny 
sacks in receptacles which protect them 
until spring, when they are set free 
It is from the germination of these 
