O BULLETIN 1434, U. S. DEPARTMENT OF AGRICULTURE 
VENTURIA LEAF SPOT 
A disease that is prevalent at times and alarms some growers is 
the Venturia leaf spot. It is characterized by conspicuous black 
spots on the lower surfaces of leaves. The black color is due to 
closely packed superficial perithecia of the causal organism. There 
is no definitely outlined diseased area in the leaf, which in many cases 
shows no symptoms whatever of the presence of the fungus other than 
the perithecia above referred to; in other cases slight discoloration 
may be noticed on the upper leaf surface. 
Venturia is confined to leaves, so far as known, and is of little eco- 
nomic importance. 
SCLEROTINIA TIP-BLIGHT 
Sclerotinia oxy cocci Wor. causes both a tip-blight disease of the 
plant and a rot of the fruit. Since the tip-blight is of relatively 
slight importance compared with the rot, this disease will be described 
under the latter heading. 
DISEASES OF BERRIES IN THE FIELD 
Field rots are of comparatively little importance in the Pacific 
coast region. Species of Botrytis often rot berries which have been 
injured by fireworms or otherwise, and a few berries rotted by 
Phomopsis may sometimes be found at picking time. Black spot of 
the berry may occur in isolated patches. The only rot that ever 
becomes serious in the field, however, is the Sclerotinia hard rot or 
"cotton ball." 
SCLEROTINIA HARD ROT (COTTON BALL) AND TIP-BLIGHT 
The symptoms of Sclerotinia hard rot or cotton ball in the berry are 
easily recognized. At harvest time the diseased berries fail to ripen 
normally, rarely showing any red color. Soon yellowish brown areas 
appear in broad bands running lengthwise of the berry and rapidly 
spread until the whole berry is uniformly yellowish brown in color. 
The interior of diseased berries is filled with the cottony white 
n^celium of the fungus, this condition giving rise to the local name 
for the disease. 
Sclerotinia is usually most abundant in young bogs or in those 
which are made up largely of young growth following heavy pruning 
and resanding. The prevalence of cotton ball during any given season 
depends to a large extent upon favorable weather conditions occurring 
at critical times in the life history of the fungus. The total annual 
loss from the disease probably never is large, but occasionally it 
becomes epidemic in areas of from 1 to a few acres and may affect 
90 per cent or more of the berries in these areas. Berries rotted by 
this fungus have to be sorted by hand, necessarily an expensive 
operation. 
The life history of the fungus {Sclerotinia oxycocci Wor.) causing 
hard rot and tip-blight will be given somewhat in detail, since there 
is no published account of the disease based upon continuous obser- 
vation in the field. Mature apothecia were first found under natural 
bog conditions on May 16 in 1923 (others evidently had matured 
earlier than this), on April 1 in 1924, and on April 18, 1925. It may 
be stated, then, that the apothecia mature as a rule in April and 
