Report on the Agricultural Experiment Stations, 1952 Page: 57

REDUCING LOSSES FROM PLANT DISEASES 57
Tomato-disease control
In 1947, after several years' tests by the New York State station, a
split schedule of ziram and copper, applied in the order of ziram,
ziram, copper, ziram, copper, proved to be the most effective spray
schedule for the control of the three major tomato diseases in western
New York-early blight, late blight, and anthracnose. Only during
the last 2 years has any single fungicide or combination of fungicides
proved superior to this schedule insofar as disease control and yield
were concerned when applied in a five-application schedule. Recently
"Manzate" and Orthocide 406, two new materials, have given control
of early blight and anthracnose equal to that of the split schedule, and
in addition, have resulted in better yields. Indications are that application
of these two spray materials will give even better results than
the ziram-copper schedule.
Experiments conducted during the past 2 years show that it is the
amount of actual fungicide used per acre that determines the disease
control, and not necessarily the amount of water per acre that is used
in applying these materials. For instance, 4 pounds of a fungicide
such as Manzate applied in 100 gallons of water per acre has given as
good control of early blight and anthracnose as the same amount of
fungicide applied in 200 gallons of water per acre.
The Indiana station reports that approximately $25 per acre spent
for spraying to control diseases of tomatoes resulted in the production
of an additional 5/^ tons of fruit per acre. Tomatoes sprayed
five times yielded from 11.9 to 12.6 tons per acre, varying somewhat
with the kind of spray used.
Lettuce diseases controlled
The cause of a leafspot disease plaguing coastal California lettuce
growers for more than 20 years is no longer a mystery. It was recently
found that a Stemphylium fungus makes the brown, scorched spots
on leaf-type lettuce. Turning under these diseased leaves before
planting a new crop reduced the spread of the disease. The Arizona
station found that preplanting surface applications to the soil of
"Aero" calcium cyanamide (20.6 percent nitrogen) at the rate of 1,000
pounds per acre, effectively controlled lettuce drop.
Diseases of Ornamentals
Gladiolus plantings, the Wisconsin station found, are potential
reservoirs of bean virus 2, tobacco ringspot virus, and cucumber virus
1. This was the first record of gladiolus as a host of tobacco ringspot
virus.
The Colorado station recently obtained strong evidence that the
carnation mosaic virus may be transmitted from plant to plant
through root grafts. Repeated tests in insect-proof cages gave added
evidence that the carnation mosaic virus may be transmitted through
roots. There is no evidence that the virus was carried from infected
plants by the soil solution. Further work by the Colorado station
indicates that ultra-violet light may prove to be a rapid means of diagnosing
carnation mosaic. Extracts of mosaic-infected plants fluoresce
a light pink at the interface between the water and the butanol. Solutions
from virus-free plants have no similar fluorescence.