TECHNICAL BULLETIN NO. 672*^» C^VÄS^^^a^f^ .%.RIL 1939 UNITED STATES DEPARTMENT OF AGRICULTURE WASHINGTON, D. C. VAPOR-HEAT TREATMENT FOR THE CON- TROL OF NARCISSUS BULB PESTS IN THE PACIFIC NORTHWEST' By RANDALL LATTA, ai^sisiant eniornologisi, Division of Truck Crop and Garden Insect Investigations,^ Bureau of Entomology and Plant Quarantine ^ CONTENTS Page Paga Introduction 1 Host tolerance to vapor-heat treatment 15 Type of equipment and its opération_. 2 Treatments of bulbs intended for flower Kxïwriments in pest control by vapor-heat production. ___ 16 treatment -_ ^ Treatments of bulbs intended for field Merodon eqiieKtris 7 planting M Eumenis tiiberculalns and K. siriçatus..:. il Advantages of vapor-heat treatment 51 Tarsonemits approximatus narcissi - 11 Summary -. 52 Jihizoglyphus hyacinthi -- 13 Literature cited 52 Ditylenchus dipsaci 15 INTRODUCTION In 1930 experimental work was begun at Sumner, Wash., {3, 4)* to determine tlie possibility of using the vapor-heat method for freeing narcissus and other bulbs from various pests inhabiting the inner scales. This method was adapted intact from Florida, where it had been developed during the Mediterranean fruitfly campaign to guaran- tee fruit safe for shipment and where it had been tested in a preliminary way on bulbs. Thermal disinfestation has long been practiced by immersing bulbs in warm water, but the wetting of the bulbs introduces several draw- backs. As long ago as 1919, Van Slogteren (7) reahzed this fact and made extensive experiments in sterilizing narcissus and hyacinth bulbs in an incubator using dry heat. The bulbs were exposed for periods of 12, 24, 36, and 48 hours at temperatures ranging from 108° to 122° F. As a result of these tests he tentatively recommended treating the bulbs for 24 hours at 113° to 115° in a heated warehouse to obtain control of the bulb nematode. There was a considerable loss 1 SubmiUwi for publication August 12, l»a8. ,„ ,„„ ! TransferrMl to Division of Control Investigation.s November 16, 1937. , , j ,, Í acknowledgments are due to A.C. Baker, who suggested the )nitiation of the project and procured the original Cduipinent; to M. B. Parker for setting up the original equipment and supervising the "«'chamcal oiCTation during the first season; to C. F. Doucette, under whose direction this work was planned and cSed out; t > Ralph Schopp and K. H. Nelson for aid in the supervision of certain commercial operations; knd appreciation and thanks are due to the growers in Oregon and W ashmgton who loaned or donated bulbs for treatments on a commercial scale. r", .i i^o ' Italic numbers in iiarcntheses refer to Literature Cited, p. o¿. 107718°—39 1 2 TECHNICAL BULLETIN 6 72, U. S. DEPT. OF AGRICULTURE of bulbs following this procedurp, but Van Slogteren believed that these were already weakened from other causes and that the stock was benefited by tlieiV elimination. The idea was apparently abandoned as far as narcissus was concerned, for his later reports are confined to discussions of the hot-water method. Dry heat has been recognized as a valuable control measure for certain insects, principally those affecting stored products, but the writer is unaware of any applica- tion of this treatment to bulbs other than that made by Van Slogteren. From 1930 to 1935 over 1,000 tons of narcisstis bulbs were treated in the Puyallup Valley under the supervision of the laboratory staff, and 903 individual experiments were conducted by the author. These included tests on heat pcMietration into the bulb; insect, mite, and nematode mortality; and plant tolerance. The matter of plant toler- ance was more difficult to determine than that of the lethal tempera- tures and exposures necessary to kill the various pests, because the tests were necessarily tedious, and entailed considerable care and time in the cidture of the plants. Since these tests have covered most of the essential phases of the problem as far as narcissus bulbs are concerned, the data accumulated during these 6 years, exclusive of the nematode-control studies, are presented in this bulletin. Spruijt and Blanton have conducted similar tests under eastern conditions, and these have been reported elsewhere (5). All temperatures are given in degrees Fahrenheit. TYPE OF EQUIPMENT AND ITS OPERATION The yapor-heat method involves the use of a treating room designed to receive conveniently containers of the type used for handling the material to be sterilized, and a machine which circulates throughout the room a mixture of air, saturated water vapor, and water in the fonn of a fine mist, all at the desired temperature. The mixture is with- drawn from the lower part of the room, circulated through the con- ditioning machine, and reintroduced into the room through the ceiling (fig. 1). The essential point in designing the treating room is to assure an even distribution of the circulating mixture. This is accomplished by apportioning the amount of mixture drawn from each part of the room by a system of channels leading to the suction outlet. Several types of rooms have been stiggested (2) but the two used in the experimental work discussed herein were square, one 12 by 12 by 8 feet and the other 5 by 5 by 4 feet, inside measurements. The walls were double and insulated. In the larger room a slatted false floor, made by spacing narrow boards 1 inch apart on 2- by 6-inch joists, was laid in two sections. The outlet was at the center of one side (opposite the door), and the outlet duct was built inside the room to avoid the formation of pockets in the adjacent corners. The joists radiated from the open- ing, dividing the floor space into equal parts, with shorter joists further dividing the larger spaces thus created (fig. 2). This arrangement must be exactmgly planned, or a cold spot is likely to occur in some part of the room owing to lack of proper apportionment m the air removal. VAPOU-HKAT ÏUEAÏMEN,T l-'Olt NAllOISSUS 15UL15 l'ESÏS 3 The coiulitioniiig machine used on this equipment consisted of a sheet-metal box 5 feet long, 3 feet wide, and 3 feet high. The mixture entered one end, passed through steam and cold-water sprays, through baffles, through a radiator, and into the treating room. The circula- tion was provided by a multivane fan which had capacity sufficient to remove the total air content of the empty room three times per minute. The conditioner, on top of the treating room, was operated by automatic valves regulated by a thermostat placed in the circulation stream as it entered the room. The mixture entered the room through a square vent in the center of the ceiling and was disseminated over the room by a flat plate, FlGÜBE 1. —Vertical section of the larger type of vapor-heat equipment used, showing location of conditioner and details of circulation. slightly larger than the opening, suspended about 6 inches below the ceiling. The plate was perforated to allow a small portion of the mix- ture to flow downward into the center of the room. This room when filled to its capacity held 39 stacks of standard-size bulb trays (18 by 27 inches) stacked 10 or 11 trays high, with sufficient clearance for handling. With each tray holding an average of 40 pounds of bulbs, such a load would weight approximately 8 tons. A similarly equipped room erected by a firm of bulb growers in the Puyallup Valley was iC>}i by 16K feet, and handled about 12 to 14 tons per load. Shallow trays 2 by 4 feet were used in this e(|uipment. After completing a number of tests on a commercial scale with these outfits, a small one was constructed to use for experimental TECHNICAL BULLETIN 6? U. S. DEPT. OF AGRICULTURE lots. This room was 5 by 5 by 4 feet, with the outlet in the center of the floor, the conditioner upright at the back of the room, and the fan at the center of the ceiling. The arrangement worked satisfac- torily (fig. 3). To obtain temperature records from within the treating room, electrical resistance thermometers were inserted in the centers of dormant bulbs and placed in representative locations throughout the treatment room. The wires ran to the outside, where readings were made periodically and recorded on prepared fonns. In commercial operation with capacity loads of bulbs, several features were found to contribute to more efficient operation. The load was heated more rapidly if the mixture in the treating room was kept foggy at all times; the more clearance between the top of the load and the ceiling of the room, the more rapid was the mass heatnig; the heating of the center of the room could be regulated by tlie size and number of per- forations in the pliito beneath the opening; the mass heating could be hastened by increasing the speed of the fan. If the trays were stacked on the open floor, tlio lower trays were the last to heat. Later tests showed that when the stacks were placed on a f ram c 8 inches high designed for use with a loading truck, heating oc- curred rapidly at the bottom, whereas the center trays of the stack were the last to rise to the treatment FIGURE 2.—Floor plan of vapor-lioat c(]iiipuieiit with temperature. ■side outlet, showing tho arraiigciiieiit of joists beneath the slatted floor which directs the circulation toward Small quantities of the duct. bulbs would dry with- in a short time aftei- bcuig removed from the room, but with capacity load a necessary l)ractice was to dry the bulbs so that they could be returned to the storage shed.