400 OHIO EXPERIMENT STATION: BULLETIN 214 
Downy Mildew (Plasmopara viticola (B. & C.) Ber. & D’Ton) of the grape is 
a prevalent fungus disease which has long been known and repeatedly studied. 
By it the leaves are attacked and the fungus forms in them éospores by which 
the winter is passed. The fungus also attacks the berries, causing brown-rot. 
Gathering and burning the fallen leaves may therefore be useful. No par- 
ticular difficulty attends the prevention of downy mildew if spraying is 
thoroughly done. 
Fig. 53. Leaf and stem of grape attacked by Black-rot. The lesions in the stem 
are dark colored. Those in the leaf show as dying areas. 
Powdery Mildew (Uncinula necator Schw.) is likewise prevalent upon both 
leaves and fruit. Like all powdery mildews the parts attacked are covered over 
by the web-like threads of the mildew fungus. This is successfully prevented 
by the use of Bordeaux mixture as elsewhere directed. (For illustrations of 
grape diseases see Report U. S. Dept. of Agriculture 1886 and 1887; also 
Scribner, ‘‘Fungus Diseases of the Grape, etc.’’). 
Stem Cankers. Stem cankers of the grape are rather frequent. Many of. 
these are due to injury caused by freezing by which dead spots are produced 
and in the process of healing these injuries become surrounded by excessive 
growth and enlargements. In some instances the enlargements obtained a 
diameter of two or three times the size of the stem. The preventive measures 
are the same as for any freezing injury, viz., drainage and prevention of ex- 
cessive late growth. 
