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404 OHIO EXPERIMENT STATION: BULLETIN 214 
LETTUCE 
Anthracnose or Leaf Perfora- 
tion. This disease of lettuce was 
discovered by the writer in 1896 
and sent to Dr. J. B. Ellis for 
description of the fungus (Mar- 
sonia perforans E. & E.) It 
shows upon the lettuce plants 
as dying of spots in the leaves 
which break free and drop out. 
The fungus also produces lesions 
in the midrib of the leaf. In 
cases of young leaves the attacks 
of the fungus causes distortion 
of the leaf, especially toward the 
top. Apparently very few plants 
recover after being once attacked, 
although one may reasonably 
keep down this disease in the 
seed beds and young plants by 
the use of Bordeaux mixture. 
For houses once_ seriously 
infested, thorough fumigation 
and soil treatment would proba- 
bly be profitable. It is not gen- 
erally distributed. 
Downy Mildew (Bremia Lac- 
tucae Regel) is the work of 
another fungus which belongs to 
the same class as the downy 
mildew of the cucumber. It forms 
yellow spots in the upper leaf 
Fig. 55. Lettuce leaf attacked by Anthracnose. surface which appear below as 
Ake ne Bk Lae by this esas erorad break whitened, downy covered areas. 
On the midrib the lealone are decp-arated. ‘The ewo ike the downy mildew of 
celled spores are shown highly magniged. From Bulletin Cucumbers this one may spread 
73. very rapidly under favorable 
conditions, such as warmth and 
surface watering in the greenhouse. Keeping water from the foliage by sub- 
irrigation of the beds has been found very beneficial (Bulletin 73), Gathering 
and burning the diseased leaves or plants will usually repay the labor. 
Particular attention to heat and moisture will usually render spraying 
unnecessary and it is certainly inadvisable except to eliminate the fungus 
from the house. Avoid too high temperature or too much moisture on plants. 
Rosette or Rhizoctonia. This is a very troublesome disease of greenhouse 
lettuce which arises from the accumulation of the sterile fungus (Azzoctonia sp.) 
in heavily manured soils used for continuous greenhouse culture. Upon the 
young seedlings the Rosette fungus produces stem lesions and rotting off or 
damping off of the plants (Fig. 57) or with larger plants which are later attacked 
upon the branch roots or rootlets, the restricted root development prevents growth 
of the plant axis and gives a basal development of normal leaves with a rosette- 
shortened center of leaves. Where serious, the crop is shortened very much and 
