Chapter 20

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.

=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.

=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.

=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.

=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.

=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.