LIBRARY TATE PLANTe^&A RU May 1940 CONTROL OF INSECTS ON GROWING TOBACCO PLANTS OF THE FLUE-CURED TYPE By W. A. Shands, Norman Allen, and J. U. Gilmore, Division of Truck Crop and Garden Insect Investigations The most important insect pests of the growing tobacco plant of the flue-cured type are the tobacco flea beetle (E pitri x paryula (F.)), the tomato and tobacco worms (P rotoparce sexta (Johan.) and P. q uinquemacul ata (Haw.)), and the true and false tobacco budworms ( Heliothis v irescen s (F.) and H. armigera (Hbn.)). HELPFUL MEASURES FOR REDUCING INSECT INJURY In the plant beds . — Whenever possible, select a new site for the plant bed. If this is impractical, avoid covering the old bed site "with stable manure or plant refuse during the summer months. Burn or steam the bed areas prior to planting so as to destroy any insects that are in the upper layers of the soil. Use boards for the side walls and see that these are well banked with soil outside and fitted tightly at the corners so as to prevent entry of insects. Use a good grade of cheesecloth con- taining at least 25 strands per linear inch .for the bed cover. See that the cover extends well over the tops of the side walls and is fastened securely on the outside. Growers will find that the tightly constructed plant bed will eliminate to a large extent the flea beetle damage to very young plants frequently experienced in loosely constructed plant beds. In the field . — Destroy the tobacco stalks immediately after harvest. This will eliminate an important food supply of several kinds of injurious insects of tobacco. Deep and thorough fall plowing, where agronomic con- ditions permit, followed by a suitable cover crop, will destroy many insects and render the fields less suitable as hibernation quarters for insect pests. THE TOBACCO FLEA BEETLE The tobacco plant is subject to injury by the flea beetle from the time the seeds germinate until the crop is harvested. T he adult can, - 2 - and frequently does, completely destroy small plants in beds. As the plants grow and beetle larvae develop and become more numerous, their injury to the plant roots, together with injury by the adults to the plant tops, causes a retardation in the growth rate and also weakens the plant for trans- planting. Recent studies have also shown that the tobacco plant bed is an important breeding ground of these beetles, particularly during the early part of the season, because from the plant bed they can emerge and move to tobacco growing in the field. Besides protecting the tobacco plants before transplanting them he grower should destroy all the plants in the beds as soon as transplanting has been completed in order to remove these plants as a source of breeding material for the flea beetle. Newly transplanted tobacco is especially susceptible to injury from feeding by the adult beetle on the plant foliage and by the larvae on the roots and in the stems. The adult and larval stages of this beetle are capable of completely destroying the stand under certain conditions. Even though the plant may not be destroyed it may suffer permanent injury or be weakened to such an extent that its rate cf growth will be materially re- tarded. The control of even light infestations on newly set plants should serve to reduce the number of flea beetles that would deposit eggs from which later generations of the insect can be built up. Severe beetle injury to the foliage cf the growing tobacco plant reduces both yield and quality. In instances of extreme injury the leaves cannot be properly cured, and as a result that portion of the crop becomes a total loss. CONTROL OF THE TOBACCO FLEA BEETLE In Plant Beds Flea beetles can be controlled by dusting with a rotenone-bearing dust or with a mixture of paris green and lead arsenate. Either of these dusts may be used on the young plants in the beds, but, because of the objection- able residue, the paris green-lead arsenate mixture is not recommended for use on the growing crop in the field. Rotenone-b eari ng dusts. — Dust mixtures containing 1 percent of rote- none, prepared with cube or derris, should be applied at the rate of one-half pound per 100 square yards of plant bed with a rotary type, hand-operated duster. The application should be repeated about every 4 days until the infestation has been checked. This dust mixture can be applied through the cloth cover of the plant bed, provided the cover is dry and is not resting on the plants. Arsenical dust. — A dust mixture containing 1 pound of paris green and 5 pounds of lead arsenate should be applied with a rotary type, hand- operated duster at the rate of one-half pound per 100 square yards of plant bed. The application should be repeated every 7 to 10 days until the in- festation has been checked, unless the occurrence of rain necessitates more frequent application. - 3 - Note . — Special care should be exercised to obtain a thorough, even distribution of dust over the plants. With a reasonably tight bed, ap- plication of the rotenone dust will be satisfactory as long as the cover re- mains in place. Rotenone-bearing dusts give a quick kill and are therefore valuable in the protection of young plants. When the cover is removed for hardening of the plants, the paris green-lead arsenate dust mixture is recommended because, in addition to being toxic to the beetles, this ma- terial repels them. On Newly Set Plants Rotenone-bearin g dusts . — Duxt mixtures containing 1 percent of rote- none, prepared with cube or derris, should be applied at the rate of 3 pounds per acre by a plunger type of duster, or at the rate of 8 pounds per acre by a rotary type, hand-operated duster. The application should be repeated about every 4 days until the infestation has been checked, as rotenone-bear- ing dusts are not effective after 4 days. Arsenical dusts .--A dust mixture containing 1 pound of paris green and 5 pounds of lead arsenate should be applied in the plant bed immediately before the plants are pulled, or to the plants in the field immediately after they are set. When applied to the plant bed, the dust should be dis- tributed by a rotary type hand-operated duster at the rate of 1 pound per 100 square yards of plant bed. Special care should be exercised to insure thorough dust coverage of the stems and leaves of the plants and to prevent excessive deposits of dust on the exposed leaves, When the application is made immediately after the plants are set, it should be at the rate of 2 to 3 pounds per acre if a plunger type of duster is used, or at the rate of 7 to 8 pounds per acre if a rotary type, hand-operated duster is used. On Field Plants Rotenone- b eari riFi; dusts. — Dust mixtures containing 1 percent of ro- tenone, prepared with cube or derris, should be applied by a rotary type, hand-operated duster at the rate of 8 to 10 pounds per acre, depending upon the size of the plants. The application should be repeated about every 4 days until the infestation has been checked, and the dust should be directed so that it will fall where the flea beetles are feeding on the plants. H0RNW0RMS Hornworms are an ever-present problem in the flue-cured tobacco areas of Georgia, Florida, and South Carolina, and in the coastal plains areas of North Carolina and Virginia. While injury by this insect does not assume major proportions during the early part of the season over much of the Piedmont areas in North Carolina and Virginia, it is frequently of major economic importance during the latter part of the season, particularly on late tobacco. Injury by hornworms is very noticeable because large sections of leaves that are located principally in the upper part of the plant are consumed. Owing to their ravenous feeding habits, a few larvae may cause a definite reduction in yield. - 4 - CONTROL OF HORNWORMS ON FIELD PLANTS C ultural control . — Fall plowing of tobacco fields will materially reduce the overwintering populations of hornworms, and it is recommended that emphasis be placed on this method of control. Hand-picking . — The control of hornworms by hand-picking, as generally practiced on small acreages, is profitable. During certain periods, however, applications of insecticides are necessary under these conditions. Cryolite spray mixture . — Use 6 pounds of cryolite containing at least 85 percent of sodium fluoaluminate to each 50 gallons of water. This mixture should be applied with either a traction or power sprayer at the rate of 60 to 70 gallons per acre for full-grown tobacco. Depending on plant size, lighter rates may be used on immature plants. A sufficient number of nozzles, properly spaced and arranged, is essential in obtaining satisfactory plant coverage by the spray. Experiments have indicated that more thorough coverage of the plant can be obtained by directing the spray toward each side of the plant, with the angle of the nozzles varying with the angle of the leaf. The spray should enter the plant on a plane parallel to the leaf axis. The distance of the nozzles from the plant at the time of spraying should be increased with the size of the plant. A nozzle should be used for each 12 to 15 inches of plant height. Consequently the number of nozzles used to apply the spray satisfactorily to one side of the plant will depend upon the height of the plant. Figure 1 is a sketch showing a suggested arrangement of nozzles for the application of spray to mature tobacco. BUDWORMS Injury by the budworms, while of greatest importance in the south- ern and eastern sections of the flue-cured tobacco area, is of major eco- nomic importance over the entire flue-cured belt. Small holes made by the larvae in the budding leaves increase in size as the leaf grows. - 5 - CONTROL OF BUDWORMS ON FIELD PLANTS Poisoned bait . — A satisfactory poisoned bait for budworms can be prepared by thoroughly mixing the following ingredients: Corn meal 75 pounds Lead arsenate 1 pound (mix and apply dry) For small quantities use: Corn meal 1 peck Lead arsenate Z\ ounces or 6 heaping teaspoonfuls In the application of this poisoned-bait mixture for budworra con- trol a generous pinch (about one-half teaspoonful) of the dry mixture should be placed in the center of the bud or tip of the plant. A satisfactory rate of application is about If pounds per 1,000 plants. Under most con- ditions control can be obtained with one or two applications. It should be pointed out that the effectiveness of this treatment will depend upon a thorough distribution of the lead arsenate in the corn meal and upon placing a pinch of the mixture in the center of each plant bud. CONTROL OF CUTWORMS Poisoned bait . — A satisfactory bait may be prepared by thoroughly mixing the following ingredients: Wheat bran (free of shorts) 50 pounds Paris green 1 pound Water to moisten 5 to 6 gallons Caution. — In the preparation of poisoned baits for cutworms, grass- hoppers, and green June beetle larvae, use wheat bran that is free of shorts, as excssive amounts of shorts in the bran will, when water is added, cause lumps to form in the mixture and make its proper application difficult. In Plant Beds Injury to plant beds by cutworms is likely to be serious, as ex- tensive damage may occur within a short time. Some cutworms overwinter in the soil as larvae, and as soon as the temperatures are favorable they become active and feed greedily, while others overwinter as pupae, and the adults emerge late in the winter and lay eggs in time for the larvae to develop enough to cause serious damage early in the spring. Even though the plant beds have been thoroughly sterilized by burning or steaming, they should be watched carefully for cutworm damage, and at the first indica- tions of such damage the poisoned bait should be applied evenly over the whole bed at the rate of 4 pounds (dry weight) per 100 square yards. OT xrss£«rr BOARD - 6 - On Newly Set Plants Cutworms may be especially destructive to newly set plants when tobacco follows a winter cover crop, particularly when the cover crop has been turned under immediately prior to the setting of the tobacco. The most effective insurance against injury by cutworms to newly set plants is to apply the poisoned bait a few days before the plants are set. The bait should be broadcast at the rate of 15 to 20 pounds (dry weight) per acre. Since many cutworms are active at night, the application of the bait late in the afternoon should give the best results. Cutworms may also damage the plants some time after they are set. Often this damage occurs only in spots in the field, and in such cases a small quantity of bait may be scat- tered immediately adjacent to the plant for its protection. If the infesta- tion is general, however, the bait can be dropped near each plant as in the case of spotted infestation. However, care should be exercised to see that only a minimum amount of the bran carrying the poison hits the plants, as injury may result if the bran lodges on the plant in any quantity. CONTROL OF GRASSHOPPERS Poisoned bait . — A satisfactory poisoned bait for grasshoppers can be prepared by thoroughly mixing the following ingredients: Wheat bran (free of shorts) 50 pounds Paris green 2j pounds Cheap syrup 3 quarts Water to moisten 5 to 6 gallons In Plant Beds Apply the poisoned bait by hand to bare spots in the plant bed and to a strip just inside the plant-bed walls. Apply the bait, also, in a narrow st rip outside the plant-bed walls. Ca ution .— This bait should not come in contact with the plants, as severe burning from the action of the paris green may result. On Newly Set Plants If grasshoppers are abundant in a field adjacent to the one to be set in tobacco, an application of poisoned bait should be broadcast over the adjacent field before the plants are set. If an outbreak of grasshoppers occurs later in the season, apply the bait to the middle of the rows only. Scattering the bait around the edges of the field is also important. The ap- plication should be made at the rate of 20 pounds (dry weight) per acre. CONTROL OF MOLE CRICKETS ON PLANT BEDS Poisoned bait . — Use the following ingredients: Corn meal or cottonseed meal 5 pounds Wheat bran or shorts 5 pounds Calcium arsenate ■§• pound Molasses 2 quarts (approximate) - 7 - Mix well and apply within 48 hours, at the rate of 3 to 4 pounds per 100 square yards of plant bed. Care should be exercised to prevent the bait from touching the young plants. The bait should be strewn around the edges of the bed, in pathways, and where the stand is sparse or missing. Two or more applications may be required. CONTROL OF THE BLACK EUROPEAN SLUG ON PLANT BEDS Hy drated or air -slaked lime. — When damage is confined to margins of beds, apply the dust in a band 3 to 4 inches wide and one-half inch thick along the margin just inside the bed walls. When damage is well distributed over the bed, apply the lime over the entire surface with a duster at the rate of 4 pounds per 100 square yards of plant bed. Apply the lime when soil and plants are dry so that it will be most effective and not injure the young plants. Late afternoon is the most suitable time for making applications. CONTROL OF THE GREEN JUNE BEETLE ON PLANT BEDS Poisoned__bait . — To prepare a poisoned bait for green June beetle control, use the following ingredients: Wheat bran (free of shorts) 25 pounds Paris green 1 pound Water to moisten 2-g- to 3 gallons Apply by hand at the rate of 10 to 12 pounds per 100 square yards of plant bed. P aris gree n. — Apply in the fall of the year on the intended plant-bed locations at the rate of 1 pound of paris green per 100 square yards. The bed site should be selected in the fall on land free of June beetle larvae. These methods have not given satisfactory control in all tobacco districts, but they are based on the best information available on the control of this pest. CONTROL OF THE TOBACCO CRAMBID ON NEWLY SET PLANTS Poisoned bait . — Use the following ingredients: Corn meal 25 pounds Oil of mirbane (nitrobenzene) 1 ounce Paris green 1 pound Water 1 pint Mix the corn meal and paris green thoroughly, then add the oil of mirbane and water so as to give an even distribution of the liquid throughout the corn meal. Apply the bait to rows or hills of tobacco with a stick-can applicator at the rate of 15 pounds per acre. - 8 - CONTROL OF WIREWORMS ON NEWLY SET PLANTS Wireworm damage is greatest on newly set plants. Wireworms are apparently attracted to the plant shortly after it has been planted in the field. The control of these insects is a difficult problem, and as yet no satisfactory method has been developed which can be economically used on tobacco lands. It has been shown, however, that large, stocky plants suffer less damage from wireworms than do smaller plants. In areas known to be infested with wireworms, the selection of stocky plants for planting in such areas is to be recommended. WHERE TO OBTAIN INSECTICIDES Information regarding the purchase of the insecticide materials mentioned in this circular may be obtained through local dealers in agri- cultural supplies, seedsmen, general stores, and drug stores, or through the county agricultural agent, State agricultural experiment station, State department of agriculture, or Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture. PRECAUTIONS The recommendations given in this circular have resulted from a thorough study of each particular insect and its habits. The one who at- tempts to use them should carefully selsct the ingredients needed, see that they are thoroughly mixed in the correct proportions, and that a careful and thorough application is made. Applications of dust or spray mixtures can best be made under calm conditions and should not be attempted when there is much wind. It is especially important to use a duster or sprayer that will give a good distribution of the insecticidal mixtures. Especial care should be exercised to wash the hands thoroughly after handling, mixing, or applying poisonous insecticides, and not to inhale excessive quantities of such dusts at any time. Figure 1. — A suggested arrangement of nozzles for the application of spray to mature tobacco. mmlSiSSL 0F f lor,da ■hhhp