llustration: FIG. 126
From a healthy potato, like the one in Fig. 124, this yield was obtained]

[Illustration: FIG. 127. EFFECT OF SPRAYING
Sprayed potatoes on left; unsprayed on right]

One pint of formalin, or enough for thirty gallons of water, will cost
but thirty-five cents. Since this solution can be used repeatedly, it
will do for many bushels of seed potatoes.

=Late Potato Blight.= The blight is another serious disease of the
potato. This is quite a different disease from the scab and so requires
different treatment. The blight is caused by another fungus, which
attacks the foliage of the potato plant. When the blight seriously
attacks a crop, it generally destroys the crop completely. In the year
1845 a potato famine extending over all the United States and Europe was
caused by this disease.

[Illustration: FIG. 128. YIELD FROM TWO FIELDS OF THE SAME SIZE
The one at the top was sprayed; the one at the bottom was unsprayed]

Spraying is the remedy for potato blight. Fig. 128 shows the effect of
spraying upon the yield. In this case the sprayed field yielded three
hundred and twenty-four bushels an acre, while the unsprayed yielded
only one hundred bushels to an acre. Fig. 127 shows the result of three
applications of the spraying mixture on the diseased field. Figs. 129
and 130 show how the spraying is done.

[Illustration: FIG. 129. SPRAYING MACHINE]

[Illustration: FIG. 130. SPRAYING MACHINE]

=EXERCISE=

Watch the potatoes at the next harvest and estimate the number that
is damaged by scab. You will remember that formalin is the
substance used to prevent grain smuts. Write to your state
experiment station for a bulletin telling how to use formalin, as
well as for information regarding other potato diseases. Give the
treatment a fair trial in a portion of your field this year and
watch carefully for results. Make an estimate of the cost of
treatment and of the profits. How does the scab injure the value of
the potato? The late blight can often be recognized by its odor.
Did you ever smell it as you passed an affected field?

[Illustration: FIG. 131. CLUB ROOT]

=Club Root.= Club root is a disease of the cabbage, turnip, cauliflower,
etc. Its general effect is shown in the illustration (Fig. 131).
Sometimes this disease does great damage. It can be prevented by using
from eighty to ninety bushels of lime to an acre.

=Black Knot.= Black k