E 489 September 1939 ''^^■/^' United States Department of Agriculture Bureau of Entomology and Plant Quarantine SUGGESTIONS FOR THE CONTROL OF THE TOMATO FRUITWORMi By W. H. White, Division of Truck Crop and Garden Insect Investigations The tomato fruitworm, Heliothis armigera (Hbn.), also known as the c orn earworm and the bollworm, is a serious pest of tomatoes, regularly or at periodic intervals, in practically all sections of the United States where the tomato crop is grov/n. Studies have shown that a single tomato f ruitworm will injure an average of six tomato fruits during its development. Besides being an important pest of tomatoes, corn, and cotton, this insect attacks a great variety of other crops, including beans, tobacco, vetch, alfalfa, cabbage, lattuce, cowpeas, okra, peppers, squash, and some types of flowers. General Description of the Tomato Fruitworm The tomato fruitworm is the young or immature form of a moth. The insect overwinters successfully in the southern part of this country in the resting or pupal stage. In the more northern part of the country, where severe winters are experienced, the insect does not successfully pass a winter. Consequently, infestations which appear in the more northern States are the result of moths which have developed in the more southern States and migrated northward. The egg which is laid by the moth is about half the size of the head of the common pin. In form it is round and flattened on its bottom side. When first laid the egg is yellow but appears white against the dark green of tomato leaves. As soon as the young larva or caterpillar begins to develop in the egg it darkens, and just before the egg hatches it becomes a dusty brown color. The newly hatched tomato fruitworm caterpillar is whitish with a black head and measures only about one-fourth inch in length. When fully developed the caterpillar is about 1? inches long. The full-grown cater- pillars vary greatly in color, but in the main they are dark brown striped with green, yellow, slate, and black markings. Oftentimes the type of food on which the caterpillars feed affects their general color, and in such cases the background color may be light green marked with yellow markings. 1 This supersedes Circular E-423, "The Tomato Fruitworm," which was issued in March 1938. - 2 - The pupa or resting stage is light brown and has a form common to many other moths. The moth belongs to the group of insects commonly known as millers and has a wing expanse of about l-^- inches. The ground color is a dull brown with shades that vary from light olive green to reddish brown. Life History and Habits The eggs are laid by the moths principally on the outer leaves of the tomato plants. Hatching occurs in from 2 to 8 days after the eggs are deposited, the length of time depending on the temperature. Soon after hatching the minute larvae or caterpillars make their way to the fruit and bore in. §uch entrance to the fruit may be made when the fruit is green or at any stage of its development. Usually the small caterpillars enter the tomato under the calyx, although some of them may enter at any point on the fruit. The caterpillars grow very rapidly and usually reach full size in from 13 to 28 days after hatching, again depending upon temperature conditions. The increase in size is accomplished by the process known as molting. Every 2 to 5 days the old hard skin is split down the back and cast off, after which the caterpillar expands greatly in size before the new skin becomes hardened. Five such molts usually occur during the period of growth. During the process of molting the caterpillars usually desert the tomato in which they are feeding and enter a new one. Also, if the tomato becomes sour or overripe, they will leave it and attack a new one. When full grown the caterpillars leave the tomatoes and enter the soil. They work their way into the soil to a depth ranging from 1 to 9 inches, depending upon the hardness of the soil, the moisture, and the weather. Each larva then forms a cell. In order that the future moth can make its way to the soil surface, the caterpillar constructs a smooth open passageway to within approximately one-half inch of the soil surface. It then returns to the cell, where it transforms to a pupa. During this inactive stage the great change takes place by which the caterpillar becomes a moth. When the changes are complete the moth emerges from the pupal skin and makes its way to the surface, where the wings expand and harden. In midsummer the period from the time the caterpillar leaves the tomato until the moth emerges may be as short as 2 weeks and under cooler conditions it may be 4 weeks. Soon after the moths emerge, mating takes place and the egg laying begins to start another generation or life cycle of the tomato fruitworm. There are several complete life cycles during each season, the number depending on weather conditions, but, beginning with the caterpillars that become full grown in September and go into the soil, many remain in the pupal stage over winter and, in favorable climates, emerge as moths the following spring. - 3 - Tomato Fruitworm Control The tomato fruitworm is difficult to control. Experimental tests are being conducted by the Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, on a comparatively large scale in California, Utah, and southern Indiana. The control measures suggested in this circular are based upon the results of two seasons' work and a partial third in Cali- fornia and Utah. These recommendations are not to be considered as final, because as the experimental work progresses changes may be expected. During the first two seasons' experiments tests were performed with rotenone-bearing materials, such as derris and cube, and with phenothiazine, cuprous cyanide, copper arsenate, copper cyanamid, cryolite, calcium ar- senate, and several other materials. All of these except the rotenone-bear- ing materials were of some value in reducing tomato fruitworm injury, but cryolite and calcium arsenate were most satisfactory. While the crop pro- tection obtained by the utilization of cryolite and calcium arsenate in dust mixtures, spray mixtures, and poison baits varied considerably in different seasons and on different farms, the indications are that a cryolite dust mixture containing 70 parts by weight of cryolite and 30 parts of talc gave the best yield of uninjured fruit. 2 In replicated experiments on several varieties and in several different fields the application of this mixture resulted in from 34 to 90 percent control. These figures are based upon the percentage of fruits damaged in dusted plots as compared with the percentage damaged in plots that were either dusted with a cube dust mixture or left undusted. Three brands of calcium arsenate have been used, resulting in control ranging from 30 to 64 percent. In the laboratory calcium arsenate was as toxic to quarter-grown larvae of the fruitworm as was cryolite. Results obtained during the early part of 1939 in California indi- cate that there is little or no difference in the effectiveness of dust mixtures containing natural cryolite, domestic synthetic cryolite, or im- ported synthetic cryolite, with talc as a diluent, when diluted in such a manner as to contain 70 percent. of sodium aluminum fluoride and applied at the same rate per acre. Each of these three types of cryolite were slightly more effective, however, when used in an undiluted form but did not have as good dusting qualities as when diluted. On the basis of these results it is recommended that cryolite be diluted to contain approximately 70 percent of sodium aluminum fluoride. This strength of cryolite dust mixture gave results which were superior to those obtained with undiluted calcium arsenate. The best degree of control v/as obtained with dust mixtures v/hen three applications were made at 2-week intervals, beginning when the foliage of the tomato plant measured about 1 foot across. In California, where on an average an acre of tomatoes consisted of 1,000 plants, 10 pounds of the dust mixture were used for the first application, 20 pounds for the second, and 30 pounds for the third, per acre. Both power dusters and a fan type of hand duster were used to apply the materials, and the plants were dusted from both sides at each application. A special effort v/as made to cover all the foliage. Observations showed that many of the worms obtained a fatal dose of poison when they moved over the plant. zNatural cryolite containing approximately 90 percent of sodium alu- minum fluoride, one synthetic cryolite containing about 98 percent, and another containing about 83 percent of sodium aluminum fluoride, were used in these experiments. UNIVERSITY OF FLORIDA - 4 - 3 1262 09224 6791 A bait prepared by thoroughly mixing 1 pound of cryolite with 10 pounds of cornraeal was almost as effective as the cryolite dust mixture. Promising results were obtained when 10 pounds of bran, with or without 1 quart of corn oil, was substituted in this bait for the indicated 10 pounds of corn meal. The bait was applied by hand and an attempt made to scatter the material lightly and evenly over the leaves of the plant. Three applica- tions were made as with the dust. About 40 pounds of the bait were used per acre for the first and second applications and from 60 to 70 pounds for the third application. Sprays with cryolite were also partially effective when used at the rate of 8 pounds to 100 gallons of water plus a sticking or wetting agent. CAUTION. — All the materials used in the control of the tomato fruit worm that are likely to leave a poisonous residue on the fruit should not be applied within 3 weeks of the first picking. The preliminary study on the residue problem has shown that if no applications are made within 3 weeks prior to the first picking of the fruit no excess residue is likely to be present. In instances where a residue does occur on the fruit at harvest time, the indications are that the washing process in the cannery or the wiping of the fruit for market with a cloth will practically eliminate the residue.