The midland journal., 1946-10-04
Tomato
Blight Troubles
Discussed
Disease Has Caused Heavy
Loss To Growers
Loss To Growers


mato blight troubles with the Exten-
sion Service representatives.
The County Agent opened the meet
ing and turned it over to Mr.. Francis
Stark, Extension Specialist in vege-
table crops Mr. Stark explained that
the trouble could be named late to-
mato bligt ahnd had spread all over
the Eastern Seaboard and as far west
as the Mississippi, starting at Flor
ida.
Valiant efforts to save tie crop in
many places have been Disappointing
This year the weather has been
against us. Heavy rains in May fol-
lowed by humid temperature condi-
tions in June gave the disease the
proper growing conditions. Because
of the normally relative unimport-
ance of the disease, little expensive
objective research has been made up
to this time However, certain things
have been determined. The casuel or
ganism is TIE same which caused late
blight of potatoes, but appears to be
a different strain. The strain which
causes severe losses on potatoes in
fects tomatoes only in very mild
way at first But having infected to-
matoes. transmission is rapid with
suitable weather conditions, and over
a period of several transmissions the
organism builds up virulence to the
point where it can attack tomatoes
with very serious effect.
Patkologists tell us that the fungus
spores (frniting bodies) must have
water in which to germinate, and it
takes only three hours for germina-
ton to take place. Therefore, infesta-
tion shows up in twenty four to forty
eight hours. Thus if drop of dew
forms on a leaf or fruit in the early
morning and remains there for three
hours or more, and that drop of dew
contains visable late blight spore,
that leaf or fruit will show visible
signs of infection within two days
hence. After the spore terminates.
the fungus grows into the inside of
the leaf or fruit and there continues
to grow, unmolested by the applica-
tion of sprays or dusts.
Normally, infected leaves will be
observed at the base of the plant and
underneath the plants where, due to
poor air circulation and high humidi-
ty, conditions are more favorable for
growth and development of tie fun
gus.
1t should be borne in mind that
any control measures used are at
best only prevention and not cure.
The spores are very susceptible to
dessication and are killed when the
temperature exceeds 80 degrees f.
and tn ehumidity is low. Tempera-
lures of 40 to 60 degrees F. and hu-
mid conditions are especially favor
able for the termination of the spores
and temperatures of 20 to 80 degrees
F., are favorable to the growth of the
fungus in the leaves and fruit cells.
1t is easily seen then tkat cool, moist
nights, followed by temperatures OF
warm days such as we have had in
Maryland this year are conducive to
the spread of the disease. In order to
prevent this spread it is necessary to
maintain coverage of the plants with
fungicides. Recommended dusts in
clude any insoluble copper with a
tale diluent containing SO to so
copper as metallic. Recommended
sprays include any insoluble copper
compound or Dithane-Zinz-Sulfate-
Lime. On older plants only 4-2-50
Bordeaux mixture will give satisfac-
tory control. Bordeaux should NOT
be used ON younger plants because
the lime contained in it may stunt
the growth of the plants.
The primary factors which will
measure the success of any control
program are: % Complete coverage
Of all the plants. (2) Coverage soon
enough and (3) Coverage often
enough. From observations made dur
ing the current season, it appears
that methods of fungicide application
plays an important part in the con-
troll program and that the methods of
application in order of their desira-
bility are: (1) orchard sprayer with
a boom attachment, (2) orchard
sprayer with gun, CD bean duster
with an apron, (4) airplane duster,
and (5) airplane sprayer. The last
two methods have been very disap-
pointing from the standpoint of uni
form coverage.
Little is known about the overwin-
tering of the tomato strain of late
blight in Maryland. 1t is known that
the strain will overwinter on potato
tubers. 1t probably does not over win
ter on tomato refuse or in the soil,
and does not overwinter in the seed.
However, it is recommended that a
rotation be practiced SO that toma-
toes will not follow tomatoes or po-
tatoes, and that tomatoes will not be
grown In fields on which tomato
refuse has been dumped.
1t is recommended that infected
fields be plowsd under deeply this
tall, Many growers are douhtful that