UTHOR.

CHAPTER XX

Tomato Diseases

By W. A. ORTON
U. S. Department of Agriculture

DISEASES NOT CAUSED BY FUNGI OR INSECTS

The health of tomato plants is to a large extent dependent on the
conditions under which they are being grown. The character and physical
condition of the soil, the supply of water and plant food, the
temperature and amount of sunlight, are all factors of the greatest
importance in the growth and development of the crop. When there are
variations from the normal in the case of any of these the plant adapts
itself to the change as far as possible, but its functions may be so
disturbed as to result in ill health or disease. It is in many cases
difficult to draw a line between a natural re-action of the plant to its
environment and a state of disease. For example, the trouble described
in the next paragraph seems to fall into the first class.

=Shedding of blossoms.=--The tomato is very liable to drop its buds and
blossoms and in some instances partial or total crop failures have
resulted. The principal causes are an over-rapid growth, due in many
cases to an excess of nitrogenous fertilizers, unfavorable weather
conditions, especially cold winds, continued rainy or moist weather,
which hinders pollination, lack of sunlight, or extremely hot weather.
Such shedding can be partially controlled by pruning away the lateral
branches as soon as formed and topping the plants after the third
cluster of fruit has set, and by a reduction in the use of nitrogenous
fertilizers. A failure to set fruit in the greenhouse is often due to
lack of pollination, which must be remedied by hand pollination.

=Cracking of the fruit.=--The formation of cracks or fissures in the
nearly mature fruit is due to variations in the water supply and other
conditions affecting growth at this stage. If after the development of
the outer portion of the fruit has been checked by drought there follows
a period of abundant water supply and rapid growth, the fruit expands
more rapidly than its epidermis and the latter is ruptured. Some
varieties of tomatoes are much less subject to this trouble than others
and should be given preference on this account. The grower, so far as
lies in his power, should seek to maintain an uninterrupted growth by
thorough preparation of the land, by cultivation or by mulching. If the
half-grown fruits are enclosed in paper bags, cracking may be prevented,
but at the risk of loss of