Insects Injurious to the Tomato
By DR. F. H. CHITTENDEN
Bureau of Entomology, U. S. Department of Agriculture
From the time tomato plants are set in the field until the fruit has
ripened they are subject to the attacks of insects which frequently
cause serious injury. On the whole, however, the tomato is not so
susceptible to damage as are some related crops--such as the potato.
=Cutworms.=--Of insects most to be feared and of those which attack the
plants when they are first set out are cutworms of various species. The
grower is as a rule quite too familiar with these insects, and no
description of their methods is necessary, beyond the statement that
they cut off and destroy more than they eat and re-setting is frequently
necessary. The best remedy is a poisoned bait, prepared by dipping
bunches of clover, weeds, or other vegetation in a solution of Paris
green or other arsenical, 1 pound to 100 gallons of water. These baits
are distributed in small lots over the ground _before_ the plants are
set, the precaution being observed that the land is free for two or
three weeks from any form of vegetation. This will force the hungry
"worms" to feed on the baits, to their prompt destruction. A bran-mash
is also used instead of weeds or clover, and is prepared by combining
one part by weight of arsenic, one of sugar, and six of sweetened bran,
with enough water added to make a mash. The baits are renewed if they
become too dry, or they can be kept moist by placing them under shingles
or pieces of board.
[Illustration: FIG. 35--CUTWORM AND PARENT MOTH (_Feltia subgothica_)
(From Chittenden, U. S. Department of Agriculture)]
=Flea-beetles= attack the plants soon after they are set, and their
injuries can be prevented by dipping the young plants before setting in
a solution of arsenate of lead, about 1 pound to 50 gallons of water, or
Paris green, 1 pound to 100 gallons. If this precaution has not been
observed a spray of either of these arsenicals used in the proportion
specified will suffice, repeating if the insects continue on the plants.
In the preparation of the spray a pound of fresh lime to each pound of
the arsenical should be added; or, better yet, Bordeaux mixture should
be employed as a diluent instead of water. This mixture has some
insecticidal value, is a most valuable fungicide, and is also a
powerful deterrent of flea-beetle attack, acting to a less degree
against other insects which are apt to be found on the tomato. In
applying any spray a sprayer costing not less than $7 is a positive
necessity.
[Illustration: FIG. 36--FLEA-BEETLE Does great injury to young plants.
Much enlarged. Actual size shown by line at right. (From Chittenden)]
[Illustration: FIG. 37--MARGINED BLISTER BEETLE (From Chittenden)]
=The Colorado potato beetle=, or "potato bug," sometimes injures
tomatoes, but not as a rule when potatoes are available. This suggests
the use of potatoes as a trap crop, planted in about three rows
completely around the field of tomatoes. The arsenicals used in the same
proportion as for flea-beetles will destroy the potato beetle. It is
necessary to keep the trap potatoes well sprayed to prevent them from
breeding on these plants and migrating to the tomatoes. Potato beetles
can also be controlled by jarring them from the affected plants into
large pans containing a little water on which a thin scum of kerosene is
floating.
=Blister beetles= may be controlled, under ordinary circumstances, by
the same method employed against the Colorado beetle. When they are
present in great numbers a good remedy consists in driving them with the
wind from the cultivated fields into windrows of straw or similar dry
material previously prepared along the leeward side of the field, where
they will congregate and can be burned.
[Illustration: FIG. 38--TOMATO WORM (_Protoparce sexta_) (_a_) Adult
moth; (_b_) full-grown larva; (_c_) pupa--all reduced. (After Howard, U.
S. Dept. Agr.)]
=The tomato worms=, of which there are two common species closely
resembling each other, are often abundant and destructive on tomato
foliage, particularly southward. The arsenicals will kill them, or they
can be held in check by hand-picking, a little experience enabling one
to detect their presence readily. Turkeys are utilized in destroying
these worms in the South.
[Illustration: FIG. 39--TOMATO STALK-BORER (_Papaipema nitela_)
(_a_) Female moth; (_b_) half-grown larva; (_c_) mature larva in injured
stalk; (_d_) lateral view of abdominal segment; (_e_) pupa--all somewhat
enlarged. (From Chittenden, U. S. Dept. Agr.)]
=The stalk-borer=, as its name implies, attacks the stalk, and is an
intermittent pest, though quite annoying at times. It is difficult to
combat, but its injuries may be prevented by care in keeping down, and
by _promptly_ destroying, the weeds after they are pulled or hoed out
during the growing season. If weeds are left to dry the striped
caterpillar of this species will desert them and enter cultivated
plants. Ragweed and burdock are the principal foods of this insect, and
special attention should be given to eradicate them where tomatoes are
planted. Crop rotation is advisable where this can be conveniently
practiced, and such plants as cabbage, radish and the like, onions,
beets, asparagus and celery are suggested as alternates. When the plants
are sprayed with arsenicals for other insects this will operate to a
certain extent against the stalk-borer.
[Illustration: FIG. 40--CHARACTERISTIC WORK OF THE TOMATO FRUIT WORM
(_Heliothis obsoleta_) (Redrawn by Johnson from C. V. Riley)]
[Illustration: FIG. 41--ADULT MOTH, OR PARENT OF TOMATO FRUIT WORM
(From Chittenden, U. S. Department of Agriculture)]
=The tomato fruit worm= (Fig. 40) known as the bollworm of cotton and the
ear worm of corn, is frequently the cause of serious trouble to tomato
growers, especially in the southern states, due to its pernicious habit
of eating into and destroying the green and ripening fruit. For its
control it is advisable not to plant tomatoes in proximity to old corn
or cotton fields, nor should land be used in regions where this species
is abundant until it has been fall or winter plowed. Sweet corn planted
about the field before the tomatoes are set will serve as a lure for the
parent moths to deposit their eggs, corn and cotton being favorite foods
of this species and preferred to tomatoes. The fruit worm feeds to a
certain extent on the foliage before penetrating the fruit, and it is
possible to keep it in subjection by spraying with arsenicals as advised
for the flea-beetles. It is suggested that arsenate of lead, being more
adhesive than other arsenicals, should be used for the first sprayings,
beginning when the fruit commences to form, repeating once or twice as
found necessary, and making a last spraying with Paris green within a
few days of ripening. This last poison will readily wash off and there
is no danger whatever of poisoning to human beings, as has been
conclusively proved in numerous similar cases. For the perfect success
of this remedy the last spraying is essential, as those who have
sprayed with an arsenical and have reported only partial good results
have discontinued within about two weeks of the time of the ripening of
the first fruit.
=White fly or aleyrodes.=--These minute insects are familiar to most
growers who raise tomatoes under glass. They can be held in control by
vaporization or fumigation with tobacco or nicotine extracts, or by
spraying with kerosene emulsion or the so-called whale-oil (fish-oil)
soap. Care is necessary in using the extracts that the smudge does not
become too dense and injure the plants. Before applying this remedy on a
large scale a preliminary trial should be made following the directions
on the packages, and reducing the amount if any ill results follow.
Hydrocyanic acid gas, properly used, is also an excellent remedy for
aleyrodes, aphides, "mealy-bug," and other soft-bodied insects which are
sometimes troublesome on greenhouse tomatoes.
For a complete account of the methods of making and handling
hydrocyanic acid gas, see Professor Johnson's book entitled
"Fumigation Methods," published by Orange Judd Company, of New
York. Sent postpaid for $1.--[AUTHOR.