E-547 August 1941 THE CORN EARWORM ON LIMA BEANS AND ITS CONTROL 1/ By Loyd W. Brannon, Division of Truck Crop and Garden Insect Investigations Introduction The corn earworm (Heliothis armigera (Hbn.)), also known as the tomato fruitworin and the bollworm, frequently causes severe damage to the fall crop of lima beans in eastern Virginia as well as in numerous other sections of the United States. It attacks this crop after corn in the vicinity has dried out and is no longer attractive to the moths for egg deposition. In the past five seasons in eastern Virginia an average of approximately 15 percent of the bean pods on fall lima beans were damaged by the insect. This, however, is not a true indication of the losses caused by the insect, as it fails to take into consideration the large reduction in yield resulting from injury and consequent shedding of blossoms and young pods prior to harvest. General Description of the Corn Earworm The corn earworm 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 come from moths which developed in the more southern States and migrated north- ward. 1/ A contribution from the Bureau of Entomology and Plant Quaran- tine, U. S. Department of Agriculture, in cooperation with the Virginia Truck Experiment Station. - 2 - The egg laid by the moth is about half the size of the head of a common pin. In form it is round and flattened on its bottom side. When first laid the egg is yellow, but it appears white against the dark green of bean 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 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 caterpillars 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. The pupa, or resting stage, is light brown and has a form common to many other moths. The moth, which belongs to the group of insects commonly known as millers, has a wing expanse of about 1^ inches. The ground color is usually ochraceous or buff, with shades that vary from light olive green to reddish brown . Feeding Habits and Nature of Injury The corn earworm attacks lim.a beans in the fall after corn in the vicinity has dried out and is no longer attractive to the moths for egg deposition. Damage to lima beans is caused by the feeding of the earworms on the blossoms and pods. In eastern Virginia the first eggs are usually laid by the moths on bean foliage in the last part of August or the first part of September, the majority observed being laid on the upper surface of the leaf. Hatching occurs in from 3 to 6 days after the eggs are depos- ited, the length of time depending on the temperature. Soon after hatching, the small worm, or caterpillar, begins to feed on the leaf upon which the egg was laid, later wandering about and feeding on the leaves, blossoms, and developing pods until about three-fourths of an inch in length before boring into and feeding on the contents of pods. The worms grow very rapidly and in the fall months they usually reach full size in from 22 to 28 days after hatching. The worm makes a round hole through the pod wall and often completely devours the contents of the pod. The holes vary in size, but normally they range in diameter from about one-fourth to one-half ijich and may appear at any point on the surface of the pod. Frequently pods thus affected do not contain larvae, since several pods are often damaged by one larva. The injury gives the pods a very unsightly appearance, neces- sitating hand culling prior to marketing the crop. In cases v/here wormy pods are not culled out prior to shipment, the worms present in pods enclosed ij the hampers may leave these pods and enter worm-free pods, thus adding to the damage while in transit. When the worm attacks young pods it causes many of those injured to drop. - 3 Control The control measures offered in this circular are based on the results of five seasons' work, much of which has been detailed elsewhere. 2/ These experiments show that corn earworm damage on lima beans can be appre- ciably reduced by the use of cryolite (synthetic or natural), used either as a dust, as a spray, or as a bait, if properly applied. Dusts Cryolite, undiluted Apply from 12 to 14 pounds per acre per application. Cryolite. 80 pounds Talc or sulfur, 20 pounds Apply from 18 to 20 pounds per acre per application. When prepared from commercial brands of cryolite containing 85 per- cent of sodium fluoaluminate, the second formula gives a sodium fluoalurainate content of approximately 68 percent in the finished dust mixture. If the sodium fluoaluminate content of the cryolite is greater or less than 85 per- cent, the proportions of the ingredients must be varied accordingly. Spray In general, cryolite dust mixtures, made according to either of the above formulas, have given better results than sprays in corn earworm con- trol. If the use of a spray is desired, however, the material should be applied according to the following form.ula: For large areas For small areas Cryolite 4 pounds 4 ounces (12 level tablespoonfuls) "^ Water 50 gallons 3 gallons (Based on cryolite containing 85 percent of sodium fluoaluminate) Bait Cryolite, 1 pound Cottonseed meal, corn meal, or soybean meal, 10 pounds (Based on cryolite containing 85 percent of sodium fluoaluminate) Apply 80 pounds per acre per application. Sulfur is recommended in preference to talc as a diluent for cryolite in instances where the potato leafhopper, the common red spider, or powdery 2/ Brannon, Loyd W. Control of the Corn Earworm on Fordhook Lima 5cai-.s in Eastern Virginia, U. S. Dept. Agr. Circ. 506, 14 pp., illus. 1939. 4 - mildew is present along with the corn earworm. In the case of the spray, wettable sulfur may be added to the cryolite at the rate of 2 to 4 pounds to 50 gallons of water. The baits should prove of considerable value in instances where the grower is not equipped to dust or spray, or in cases where the bean foliage has attained such dense growth that the use of horse-drawn equipment would be impracticable. They should be broadcast by hand lightly and evenly over the leaves of the plants at the same time intervals as for dust or spray applications. If the Mexican bean beetle is present in injurious numbers along with the corn earworm, the dust or spray should be used in preference to the baits, as these baits are not effective for control of the Mexican bean beetle. To secure thorough coverage of all parts of the plants, and to make the treatments effective simultaneously for control of the Mexican bean beetle, the insecticide should be directed to both the upper and lower surfaces of the leaves. This may be accomplished by making minor adjustments to the nozzles of dusters and sprayers equipped for control of the Mexican bean beetle. 3/ Treatments should be begun when the majority of the silks on ears of field corn m the vicinity of late plantings of lima beans have dried out, for it is usually at this time that the corn earworm moths begin laying eggs on beans. In eastern Virginia this usually occurs in the last part of August or the first part of September, at which time late plantings of lima beans are generally in full bloom. Treatments should be begun earlier in case the worms are observed on the foliage in injurious numbers, or if it becomes necessary to control the Mexican bean beetle. As corn earworm moths are continually emerging and depositing eggs, which are not affected by the treatment, and since new untreated foliage is constantly developing, treatments should be repeated at approximately 2-week intervals. Three treatments are usually necessary, depending on the abundance of the insect. In order to avoid the danger of harmful fluorine lesidues on the edible portions of the market product, treatments should be discontinued 2 weeks prior to harvest . Dusts should be applied when little or no wind is blowing. If rains occur within 48 hours after a treatment is given, the application should be repeated as soon as conditions will permit. Note: Results of recent experiments indicate that the cryolite treatments listed above are also effective in reducing corn earworm damage on snap beans. On account of the fluorine residue hazard, cryolite should not be applied to snap beans after the pods have begun to form. By making 3/ Howard. Neale F. , Brannon, Loyd W. . and Mason. Horatio C. The Mexican Bean Beetle in the East and its Control. U. S. Dept. Agr. Farmers' Bull. 1624 (rev.), 21 p;. , illus. 1936. - 5 - careful applications prior to this time, however, damage to this crop may be appreciably reduced. In instances where the corn earworm is present in injurious numbers along with the Mexican bean beetle, cryolite should be used in preference to the rotenone-bearing materials, such as derris and cube, for the combined control of the two insects, as the derris and cube, although highly effective for control of the Mexican bean beetle, are not effective for control of the corn earworm. Information regarding the purchase of the insecticide materials mentioned above may be obtained through local dealers in agricultural supplies, seedsmen, drug and department stores, or through the county agricultural agent. State agricultural experiment station, or State depart- ment of agriculture. «,««?'»«»• UNIVERSITY OF FLORIDA illlillilllilillllilil 3 1262 09230 3949