Trol of Narcissus Bulb Pests in the Pacific Northwest'

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 application 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 tolerance was more difficult to determine than that of the lethal temperatures 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 opening, 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 circulation 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 mixture 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 occurred 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 within 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. This was done by leaving them in the room for several iiours after treatment, usually overnight, with the fan running, but with the steam and water shut off and the door and ventilators open The bulbs at the end of a treatment are not soaked, but the surfaces are damp with condensed moisture. If quantities of bulbs are removed irom tlie room immediately following treatment, this moisture re- mains and may induce the formation of blue mold. The use of large containers such as bulb crates retarded the rate of heating, consequently shallow containers were always used. An exposure of approximately 5 hours was necessary to raise the mass tempera- VAPOR-HEAÏ TUIOATM KXT FOR NARCISSUS BULB PESTS 5

ture of a capacity load to 110° F. This period varied somewhat according to the teini)oraturo at tlic start, tlie size of the bidbs, and mechanical factors. Tlie heating' period is termed an "approach period," and all treatment ])eri()(ls noted are exclusive of tliis period. This rule holds also where experimental samples were treated without other load.

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FIGURE 3.— Vertical Kection of snmll type of vapor-heat equipment used, showing location of conditioner and details of circulation.

EXPERIMENTS IN PEST CONTROL BY VAPOR-HEAT TREATMENT Five pests commonly attacking narcissus bulbs were subjected to tests with this method. They will be discussed in the following order: (l) Merodon equestris (F.), the lai'ger bulb fly or narcissus bxdb fly; (2) Eumerus tuberculatm Kond. and /i". strigatus Fall., generally designated as the lesser bulb ilies; (3) TarKouemus approximatus narcisKi Ewing, the bulb scale mite; (4) Rhizogli/pkuti hyacinthi Bdv., the bulb mite; and (5) Ditylenchux dipmri (Kuhn) Filipjev, the bidb and stem eelworm. Exjjeriments on the control of the last named were carried on in cooi)eration with the Division of Neniatology, Bureau of Plant Industry. Since all these pests inhabit the inner tissues of the host bulb, it was decided at the outset to record the start of treatment at the time the mass temperature reached the desired treatment temperature. The heating period was termed an "approach period," and the period during which the temperature of the mass was maintained at any point was the "treatment duration." A temperature of 110° to 111 ° F. was selected as an arbitrary standard from which to work because of the general use of this point by growers conducting warm-water treatments. G 'l'KCllXlC'AL lUILLKTINT tj72, V. S. DKPT. OF .UiUHn'LTlTIÎK

To facilitate the arbitrary calculation of approach periods, a study was made of the rapidity of heat penetration into narcissus bulbs. Resistance tliernioineters were inserted into the centers of bulbs (two bulbs were reciuired to cover each thermometer), and frequent rcadinijs were made of the temperature at the bulb centers when the bulbs were directly exposed to vapor heat of 110° to 111° F. The distance from the surface of the bulb to the thermometer was recorded in each case.

FiGUKE 4,—Cro.ss section of narcissus bulb showing nearly mature larva of Merodnn eqveslríx in its center. VAPOll-HlíAT TIlKA'l'MENT FOR NAKCISSUS BULB PESTS

The initial rise in temperature was rapid, but became propor- tionately less as the bulb temperature neared 110° F. Several tests showed that the rise from 109° to 110° took nearly as long as the rise from storage temperature (58° to 63°) to 109°. By overheating the mixture 1° or 2°, the rise was uninterrupted. For this reason the usual practice was to overheat the mixture to 111° or 112° in bringing bulbs up to the desired treatment temperature of 110° to 111°. By using isolated individual bulbs it was found that from 60 to 75 minutes was necessary to raise their temperature from that of storage to 110° to 111° F. Tlie distance from the thermometer to the bulb surface ranged from 20 to 28 mm, but the variations in time were not consistent with the variations in distance to the surface, probably owing to imknown mechanical factors. MERODON EQUESTRIS The narcissus bulb fly {Merodon equestris) has only one generation per year, with the adults appearing in May and June. Eggs laid at that time soon develop into larvae that enter the bulbs before they are harvested, and the full larval period is spent in the bulb initially attacked. Usually not more than one larva occurs in a single bulb (fig. 4). Control experiments with vapor heat have been directed against the larval form because that stage is the one present during the storage season. Treatment of the bulbs following harvesting, while they are in a dormant condition, is done (1 ) to reduce the damage done the bulb by the developing larva and (2) to remove the potential source of infestation the following spring. Attempts were first made to determine the approximate lethal exposures to heat as a guide in planning subsequent experiments. This was done by removing the larvae from the bulbs and exposing them directly to vapor heat. Temperatures of 107°, 109°, 111°, 113°, and 115° F. were used and four periods of exposures tested at each temperature. At 107° an exposure of 80 minutes caused only 26.7- j)ercent mortality, but much higher mortality resulted from 60- and 70-minute exposure at 109°. Exposures of 40 minutes or more at 111° produced nearly complete mortality, and all periods of 30 minutes or longer at 113° and 115° resulted in mortahty of all larvae. These tests are summarized in table 1.

TABLE 1.—Mortalily of tmprotected larvae of Merodon equestris produced by vapor- heat treatments at different temperatures

Larvae- Duration I^arvae— Duration Mortal- i'emperature Mortal- Temperature of treat- ity (°F.) ity (°F.) raent ment Dead Alive Dead Alive

Num- Num- Num- Num- Minutes ber her Percent MinuUs her ber Percent 50 2 13 Ki 30 16 0 100 60 1 12 8 40 16 (1 100 70 2 13 13 60 16 e 100 80 4 11 27 60 15 0 100 40 6 9 40 30 15 0 lOO 60 5 10 33 40 15 0 100 i 60 14 1 93 60 16 0 100 70 13 2 87 60 16 0 100 30 11 4 73 40 14 1 93 1 50 15 0 100 60 14 1 93 TECHNICAL BULLETIN 6 72, U. S. DEPT. OF AGRICULTURE

In theory, an approach period phis the lethal periods designated in table 1 should cause complete mortality of larvae in tlieir normal environment within tiie bulbs. N'liineroiis tests were made at temperatures between 105° and 118° F., to establish the durations lethal to undisturbed larvae. The results were found to agree in general with the stated theory, it being realized that the approach period itself adds to the effect of the treatment. The tests at each temperature were made in duplicate to reduce the eiïect of variations in the length of lethal exposure. Such variations resulted from inability to establish an approach period that would apply accurately to all bulbs in an experimental sample, since there was always some variance in size even in graded bidbs, and since the method of calculating the approach period gave the temperature rise at the bulb center, although larvae were usually at some point nearer the surface. In each test 50 bulbs showing symptoms of infestation were treated, but the actual number of larvae present upon examina- tion ranged from 5 to 40, most samples having 15 to 25. Approxi- mately 1,500 larvae were used. The results of these tests are summarized in table 2.

TABLE 2.—Mortality of larvae of Merodon equestris resulting from vapor-heat treatment of infested bulbs at temperatures between 105° and 118° F.

Morlality following treatment at— Duration of treatment (hours) m^° 10B° 107° 1(18° 109° 110° 111° 112° 114° 116° 118°

Percen Percent Percen Percen Percent Percent Percent Percen' Percent Percen Percent fi) 0 92 100 1 02 100 100 K \ 100 69 100 KX> 100 75 87 1 100 1 100 56 100 100 H.... SO 1 100 86 93 100 100 100 100 lOO 100 100 100 100 100 15Í . 100 100 100 1 - ICO 100 100' VA . 100 1 __ 100 1 2 60 100 100 100 f 100 1(X) 100 2H --- 1 100 1 M Hi "*"'84" KKI 1 9.5 ( 10(1 'IM 100 1(K) f r,^ l(HI 100 100 5 SÜ S6 5« _ 92 loo -. - 1 100 1 roo 6K--- 43 loo 7 4a 7H S3 8 100 8M 92 ...... 9 91 "1 ---■ 1 -■ Í ' Approach perioflies. Inasmuch as the larvae apparently have identical habits the group is considered as a whole in these studies. E. tnberculatus is perhaps the most com-

FiüUHE 5.—Cros.s section of narcissus bulb showing larvae of Emnerm spp. feeding on bulb tissue. 1(17718°—39 :; lu TECHNICAL BULLETIN 672, U. S. UKIT. OF AGRICULTUKK

mon of the species. It and E. fitrigatus occur in the Pacific North- west. E. narcissi is apparently not yet established in this region. The lesser bulb flies differ from the narcissus bulb fly in that they have more than one generation a year, and when present in a bulb are usually in considerable numbers (fig. 5). The larvae of these species are usually associated with the occurrence of various rots, especially basal rot {1). Although not considered a serious pest in the Pacific Northwest, their potentialities as disease carriers make their control desirable. Studies on the mortality of lesser bulb fly larvae caused by vapor- heat treatment were carried on in parallel with those on Merodon equestris. The unprotected larvae were exposed to vapor heat at temperatures between 107° and 115° F. Results (table 3) were verv similar to those obtained with the larvae of the narcissus bulb fly.

TABLE 3.—Mortality of unprotected larvae of Eumerus spp. produced by vapor-heal treatments at different temperatures

Larvae— Larvae— Duration Mor- Duration Mor- Tenu)erature °P\ of treat- tality Teini)erature °F, of treat- tality ment Dead Alive ment Dead Alive

Num- Num- Percent Num- Num- Percent MintUes ber ber Minutes ber ber 40 6 45 12 1 ñU 45 5 m 45 111 107 50 5 10 \ m 49 1 60 11 39 22 20 37 13 71 20 70 29 41 113 30 47 3 94 30 17 32 35 40 50 0 40 32 18 64 50 49 1 9« 50 33 14 70 20 49 0 60 39 10 80 115 30 50 0 10(1 111 30 39 10 80 40 ,50 0 \ 40 44 6 88 50 50 0 100

Infested bulbs were also treated in the same manner as those with larvae of Merodon equestris. The bulbs were selected from stocks known to be infested with lesser biilb fly larvae and treated in a manner simulating commercial handling. A total of 7,650 larvae were used, ranging from 15 to 330 per treatment, a majority of the tests having 50 or more. In these tests (table 4), a.8 in those with Merodon equestris, a pohit was not reached at 105° F. where mortality of all larvae resulted, but at all other temperatures a complete kill was obtained within feasible limits of exposure ranging from 5 hours at 106° to the com- j)letion of the approach period only at 116° and 118°. In the case of Eumerus especially, the larvae were more often situ- ated hi the outer scales, or their feeding had destroyed part of the bulb and corisequently reduced the period necessary for the heat to reach the point at which they were located. In such cases the approach period, which was calculated on the time necessary for temperature rise at the center of the bulb, became, in part, a treating period, although it was not so recorded. For that reason many tests resulted in complete mortahty following very short treatments. But occa- sionally there were instances where the approach period did not act as a treatment, and a period much longer in proportion to the other tests was necessary. For that reason a curve was plotted on the longest minimum exposures of the group as a whole. VAPOR-HEAT TREATMENT FOR NARCISSUS BULB PESTS 11

TABLE 4.—Mortalily of larvae oj Eumerus spp. resulting from vapor-heal treatment of infested bulbs at temperatures between 105° and 118° F.

Mortality following treatment at— Duration of treatuient (hours) 105° 10«° 107° 108° 109° 110° 111" 112° 114° 116° 118°

Per- Per- Per- Per- Per- Per- Per- Per- Per- Per- Per- cent cent cent cent cent cent cent cent cent cent cent (') 0 100 100 100 91 73 100 100 \ lOO 11» 78 100 100 100 lOfl 100 1,.. 79 93 97 100 100 100 lOO iüÓ I.. .__ 100 100 1 no 100 100 lOO 100 ¡00 1 . 83 100 100 ]■-' 100 100 Í - 100 ino 100 100 1 100 Í Ui 100 100 1 100 lOO 1 100 100 •) 100 1-- 100 •>\'¿ 100 \\. - 93 m 100 4 94 99 100 100 / 96 100 100 j _. . 1 100 :M 100 t; _ 97 100 fiH--- 95 100 ■¡\^ 97

I Approach period only. Based on such a curve the following durations which will give complete mortality have been calculated for each of the temperatures from 105° to 118° F. "F îlfiurs ^F Hours 100°" undetermined 111°—1^ 106°--5 112°—1 107°--4 114°—M 108°--3 116°—approach period only 109°- -2 118°—approach period only 110°- TARSONEMUS APPROXIMATUS NARCISSI The bulb-scale mite {Tarsonemus approximatus narcissi) is a small mite that works between the scales of narcissus bulbs (fig. 6). The injury caused by these mites is principally due to their presence in large numbers. A very few of them can develop rapidly under favorable conditions to a large population capable of causing serious damage. It had been generally observed in a number of tests for other purposes that these mites were all killed at durations of more than one- half hour in vapor heat at 110° to 111 ° F. To check definitely on this point a series of experiments was performed in which infested bulbs were treated for given durations np to 30 mum tes at this temperature. Of each lot of six bulbs, three were examined within 3 days following treatment to observe the mortality of adults and larvae resulting from the treatment, and the other three held for a period of approximately 10 days to allow surviving quiescent larvae and eggs to develop into active adults and larvae. 12 TECHNICAL BULLKTIN 0 7 2, U. S. DHPT. OF AGIUCULTURK

Forms active at the time of treatment (table 5) were easily killed, but the quiescent larvae and eggs (table 6) were slightly more resistant. Each bidb as it was examined was carefully dissected and a record of the position of the mites was made, whether in the neck region, basal edge, outer scales, or inner scales.

FiGUKE G.—Narcissus bulb with outer scales partly removed to show discoloration caused by feeding of bulb-scale mites.

This mite is of particular importance because under field conditions in the Pacific Northwest the infestations usually are not sufliciently heavy to cause visible symptoms in the field. The mites will multiply under storage conditions, however, to a ])oiiit where they will cause serious damage when the bulbs uic forced in greeidiouses. Figure 7 denionstrates the serious distortion that results from such conditions. Iherinal treatments are the only known practical measures that can be employed to eliminate the pest. The efl'ectiveness of such a treatment in preventing damage was demonstrated in the forcing test shown in figure 8. VAl'OR-lllOAT TllKATMKNT FOR XAIICISSUS lUirj! I'KSTS 13

TABLE 5.—Mortality of adults and larvae of Tarsonemus approximatus narcissi produced by different durations at 110° to 111° F.

Adults Larvae Total (HI «f trciitmont Test No. (niiijutcs) tality I)CH<1 Alive 1 )ea(l Alive Dead Alive

Nnviber Number Number Number Number Number Percent 1 22 0 32 2 54 2 96 (') Í 2 18 14 16 15 34 29 54 3 16 13 12 9 28 22 56 1 21 0 10 0 31 0 100 III --, \ 2 100 0 S4 0 154 0 1Ü0 3 10 0 8 Ü 18 U 100 1 7 0 8 0 16 0 100 J(l 2 33 0 18 0 51 0 100 3 63 0 29 0 92 0 100 1 M 0 21 0 75 0 100 :((! 30 0 11 0 41 0 100 3 21 0 13 0 34 0 100

Approach period only.

TABLE (i.— The mortality of quiescent larvae and eggs of Tarsonemus approximatus narcissi produced by treatments of different durations at 110-111° F., and shown by the absence of active adults developed from quiescent larvae, or active larvae from surviving eggs, or normal-appearing eggs when examined after a suitable incubation period

Active forms Normal-ap- Degree of mor- Duration of evi)osiire (minutes) Test No. present pearing eggs tality

Number 1 1 Adults, larvae 0 Incomplete. (4) . __ __ 2 do 0 Do. 1 3 do 0 Do. 1 1 do 0 Do. 2 None 16 Do. 1 3 Adults 8 Do. 1 1 None 7 Do. 20 - --- 2 ..__do - 6 Do. 1 3 ____do. .- ^ 3 Do. 1 1 .__do.. 0 Complete. 30 2 do 0 Do. 3 do. 0 Do.

1 Approach i)€rio

FIGURE 7.—Grconliouse-forccd niircissus severely injured by the bulb scale jiiite. 1'tie injury is evidenced by twisted, distorted leaves and stems and severe reduction in the quantity and quality of flowers.

FiGUBE 8.—p:fîectiveness of vapor-heat treatment (2 hours at 110° to 111° F) in preventnig plant distortion of narcissus by eliminating infestation by the bulb scale mites. In the check sample the mites continued their development and caused considerable damage, but in the treated sample the control of the inites eliminated this distortion. VAi'OU-HKAÏ TRKATMKNÏ FOR NARCISSUS BULB PESÏ!- 15 tests, in which large bulbs heavily infested with mites were exposed to vapor heat for periods beginning with the approach period only and continuing for intervals of 10, 20, and 30 minutes, were made to determme the actual lethal duration. The results proved this mite to be very susceptible t:) a temperature of 110° to 111°. No survivors were found in any of the tests. DITYLENOHIJS DIPSACI The bulb neinatodc (Dltylmchus dipsael) has i)een recognized as one of the most serious bulb ])ests. The nematodes when present in the bulb scales are capable of destroying the bulb if allowed to develop un- molested (fig. 10). Nem- atodes that leave the bidbs may survive in the soil for extended periods and infest bulbs re- planted there. Treat- ment of the bulbs during the storage season has P'iGURE 9.—Cross section of decayed narcissus bullj been practised for the showing bulb mites feeding in the rotted tissue. elimination of the nematodes. Hot-water treatment has been the accepted method since its developmentin 1917 (6,8). In 1934 a cooperative project was inaugurated between the Bureau of Entomology and Plant Quarantine and the Division of Nematology, Bureau of Plant Industry, to determine the effectiveness of thermal treatments in the control of the bulb nematode. Briefly these tests have indicated that a vapor-heat treatment of 8 hours at 110° to 111° F. is very effective as a control of this nematode,. provided the treatments are made within a reasonable time after lifting or digging the bulbs, before the formation of the resistant quiescent stage of the nematode which develops as the storage season progresses. HOST TOLERANCE TO VAPOR-HEAT TREATMENT In addition to determining the toxic effects of vapor-heat treatment on the pests infesting narcissus, it has also been necessary to ascertain the ability of the bulbs to tolerate treatments lethal to those pests. The general experience with the hot-water method has indicated that the margin of safety between host tolerance and pest control was rather narrow, apparently varying because of several factors. IG TKCHNICAL BULLETIN 6 7 2, 11. S. DEPT. OF AORICULTUEE

It has been necessary to study the tolerance of narcissus bulbs to vapor-lioat treatment along two lines (1) treatment of bulbs intended for forcing or flower production, and (2) treatment with reference to bulb production or vegetative increase. In the first, the chief interest is in the production of flowers, but in bulb production the growth increment is primary, and incidental marking of flowers and foliage is a nonessential factor so long as the development of the bulb is normal. The attitude of the producing trade is one of reluctance in offering bulbs infested with nematodes for forcing, since there is a lack of confidence in the flowering qualities of such bulbs after their subjec- tion to the more severe control measures. Consequently the studies of treatments for forcing stocks have been contined to exposures

FIGURE 10.—Longitudinal and cross section of narcissus bulbs showing necrotic scales in the area of nomatode infestation.

sufficient to control btdb fly larvae and mites only, while treatments for planting stocks have been lengthened so as to' indicate the limits of plant tolerance, so that they might serve as a basis of studies of nematode control by vapor-heat treatment.

TREATMENTS OF BULBS INTENDED FOB FLOWER PRODUCTION

Experiments to determine the effect of vapor-heat treatment on flower production were of two types, (1) samples representing commercial planting stocks receiving a minimum 4-hour treatment and (2) _a senes of detailed treatments of known approach and treatment periods, for studying the tolerance to temperatures above and below the standard of 110° to 111° F., determining the optimum season for treatment, and comparing the effect of treatment durations ranging from 2 to 12 hours. ^ ^ VAPOB-HEAT TREATMENT FOR NARCISSUS BULB PESTS 17

These tests involved 28 experimental series including 204 individual samples of 7 varieties, 28 varietal tests, and samples representing 13 varieties from 34 large-quantity treatments.

TOLERANCE OF BULBS REPRESENTING LARGE-QUANTITY TREATMENTS Samples selected from large-quantity loads were tested for their forcing qualities. These were selected at random from commercial stocks after their removal from the treating room, consequently it was not possible to record the treatment definitely other than as the minimum after the approach period of the whole load. The established minimum treatment period was 4 hours at 110° to 111° F., and this was preceded by an approach period of not over 5 hours. Bulbs in the upper trays of a load would heat in about 1}^ hours, wliile those near the floor would usually require the ñdl approach period of 4 to 5 hours. On that basis the random samples represented durations anywhere between 4 and 7% hours at treatment temperature. Every effort was made to give these test bulbs uniform handling. Treated samples were stored next to their imtreated checks in racks built to hold Small trays containing 25 bulbs each. The bulbs were planted in flats the first week of October each year and kept covered with straw and soil until they were removed to the greenhouse late in December or in January. No attempt was made to encourage the development of early blooms, for it is common knowledge that bulbs forced too early are liable to have a long drawn-out period of blooming, with stunted growth and flowers of reduced size. The biilbs were forced at about their normal time and produced flowers in a concentrated blooming period. Each flat contained 24 bulbs in 4 rows of 6 each, round bulbs being used in almost all tests. As each bud opened the date was recorded, and 3 days later (the time of maximum development) measurements of the flower were taken, and the grade of the flower and the condition of the foliage noted. In the poetaz and polyanthus varieties, the dates of the opening of the first and the fourth florets were recorded. The flower grades were determined according to the system given in table 7. As each sample or series reached its maximum in blooming, photo- graphs were taken as a matter of record. Orthochromatic film was used, withoxit or with a filter, depending on the particular variety being photographed. It was found that for yellow trumpet varieties, a K-1 filter gave best results, whereas the contrast in bicolor, red cup, poetaz, and poeticus varieties was best brought out by unfiltered exposure. Yellow labels were found to be far superior to white, being very legible and at the same time not dominant. The flowers produced from these samples varied greatly in quality, some being perfect whereas others were decidedly modified in shape and sometimes even partly deformed. The modified portions of the flowers developed from areas that formed from the tip of the growing bud, which was within the bulb at the time of treatment. The modifications showed first as imperfections in the outline and texture of the trumpet margin, and notching of the lateral margins of the perianth segments. More severe treatment caused rough trumpet texture and a decided restriction of the flare of the tnunpet margin ¡ 107718°—39 3 18 TECHNICAL BULLETIN 6 7 2, U. S. DEPT. OF AGBICULTURE while even more severe treatment resulted in split trumpets and marked distortion.

TABLE 7.—System of grading forced narcissus flowers

Trumpet varieties Short trumpet or cup varieties Rating Grade (ïrade Condition of flower (Condition of flower No. No.

! Perfect flower. 1 Perfect flower. Flowers with slight imperfection 21 Flowers with i)erianth seg- Good (salable) in trumpet end. :!/ ments rolled or in some way slightly imperfect. ; Trumpet end untypical, texture slightly roughened, perianth segments sometimes slightly notched. 4 Decided straightening of trumi)et end, sometimes perianth seg- 4 ments notched. Imperfections severe enough Fair 5 Trumpet end with texture rough, 6 to spoil (or selling. quite untypical, perianth segments notched. 0 Trumpet rough, slight splitting. Trumpet rough, split twice. Distortions such as missing 8 Trumpet split several times. perianth segments, seg- 9 Trumpet badly distorted. ments curled in cup, etc. 10 Trumpet gone. 10]•1

Therefore it was evident that the varieties most likely to reflect injury from vapor-heat treatment were those with full trumpets and smooth texture. King Alfred is of this type; and since it is also one of the most important of the commercial forms, it has been used more, or less as an index to determine the delicate point of minimum plant injury from treatment. Other trumpet varieties that naturally have an irregular trumpet margin and rugous texture did not show detrimental effects from the less severe treatments. In the short-trumpet types (incomparabilis, barrii, and leedsii) and in poeticus and poetaz groups, where the trumpet is reduced to a cup, the effect was usually confined to the perianth segments, which were notched or rolled. In the forcing tests summarized in table 8 the difference in modification of the flowers between King Alfred and the other varieties due to the treatment, is emphasized. Excepting the four poetaz varieties and King Alfred, the other types were very little if at all modified by treatment, and even within the group of King Alfred samples there were some only slightly affected as compared with others showing severe modification. This variance was due to the fact that all sorts of cultural types were represented, since the stocks came from different growers, were harvested at different times, and were not cured to the same degree. It was observed that the effects of vapor-heat treatment varied according to the season at which it was apphed. Bulbs treated early VAPOR-HEAT TREATMENT FOR NARCISSUS BULB PESTS 19

TABLE 8.— Tolerance of forcing-stock narcissus bulbs to vapor-heat treatment [Each sample consisted of 24 bulhs, except where otherwise noted, selected from a large quantity treated in one operation]

Mini- Date of mum ex- Flowers Grade» Variety of Condition treatment posure at producer of foliage Remarks 110° F." flowers

Hours Number July 29-. 4 24 Normal... ilolden Spur 0 20 ...do Augri;: 4 25 ...do 0 20 ...do Aug. 12.- 4 21 2-3 ...do 0 20 ...do Aug. 17.. 4 23 3-7 Blotched.. Not well dried and probably 0 22 Normal... received maximum treat- Aug. 19.. 4 10 3-4 Blotched.. ment. 0 29 Normal... ÂUg;22"." 4 23 3-7 Blotched . Grown on peat .soil consequently poorly dried. 0 21 Normal... Aug. 25.. 4 21 2-3 Blotched,. Well dried. 0 27 Normal... King Alfred... Aug.31.. 4 14 3-6 Blotched.. 10 blind buds. 0 23 Normal... Sept. 1.. 4 17 3-4 Blotched.. 6 blind buds. 0 26 Normal... Sept, 8.. 4 12 3-4 Blotched.. Treatment too late. 0 26 Normal... Sept. 18. 4 16 3-7 Blotched-- Grown in southern Oregon- advanced. 0 25 Normal-.- Sept. 19. 4 15 2-3 Blotched.. Treatment too late. 0 25 Normal--. Sept. 17- 14 k 5 4-5 Blotched.. Poor stock. 0 16 2 Subnor- mal, fJuly 31.. 4 24 2-3 Mosaic Minister Talma 0 19 2 -.do {Aug. 17.- 4 20 2 Normal..- Sir Francis Drake 0 22 1 ..do fAug.^.. 4 26 1 ..do 0 25 1 ...do July 30.. 4 25 1-3 ...do 0 22 1 ---do Äug'16.; 4 23 2-4 .-.do 1) 24 1 --do- Aug. 4.- 4 13 2 ...do .- Few blooms due to small size of bulbs. V'ictoria 0 12 1 --.do Äug^sV. 4 23 2-3 ...do 0 23 1 ...do Äug'6." 4 17 2 ...do Do.' U- 0 16 1 ...do (Sept. 14- 4 10 2 --.do 11 blind buds. Do.« 0 17 1 ---do Aug. 11.- 4 24 2 ...do .- Slight notching of perianth segments. Sir Watkin 0 23 1 ...do Sept, 15- 4 24 2 ...do 0 23 1 ...do Sept, 22- 4 0 Stunted... Bulbs had sprouted noses when treated. 0 39 1 Normal... Aug. 21- 4 24 1 ...do.- Average number of florets reduced from 6-7 t» 3-4. 0 23 1 ...do Sept. 17- 4 7 2 —do Number of florets reduced. 0 24 1 ..do Sept. 1Í. U'A 18 2 ---do- - Do. 0 25 1 -.do Sept. 23. 4 2 2 ...do I 0 28 1 —do Sept. 16. 4 10 2 Blotched-. Bulbs had .sprouted noses 0 33 1 Normal... when treated. Sept. 24. 4 6 2 ...do- 0 26 1 -.do Aug. 3.- 4 21 4 ...do 0 22 4 --do Tetamonius Pienus— Sept. 11. 4 22 4 ...do 0 26 4 —do..

1 Zeros in this column represent untreated checks. ' Sample contained only 18 bulbs, I For system of flower grades see tfehlB 7. t Sample contained only 20 bulbs. 20 TECHNICAL BULLETIN 6 7 2, U. S. DEPT. OF AGRICULTURE in the storage season, or treated when insufficiently dried, produced flowers with roughened trumpets and modified trumpet margins. The efl'ect on the flower was least in treatments made in the middle of the storage season or later. In treatments made the latter part of the season, a reduction often occurred in the quantity of blooms, owing to buds coming blind (ones with a normal stem but an empty sheath). In early varieties blind buds occurred following treatments as early as the middle of August, whereas in medium- and lato-flowcring

FIGURE 11.—Blotching of leaf tips caused by vapor-heat treatment, a condition which usually appears only in stocks treated after midseason. varieties a reduction in the number of blooms was not caused until by treatments made late in September. The flowers in the cases of late- season treatments were usually of good quahty, even in instances where a severe reduction in quantity occurred. A blotching of the leaf tips (fig. 11) usually accompanied the appearance of blmd buds. In many instances blotching of leaf tips occurred where blmdness did not, which allowed its occurrence to be VAPOR-HEAT TREATMENT FOR NARCISSUS BULB PESTS 21 used as an indication that the optimum season for treating had been passed and that the treating date in question was near the point where blindness would have resulted from treatment. In varieties where the flower bud appears ahead of the foliage, such as certain poetaz types, severe reduction of the quantity of flowers sometimes occurred when the leaf tips were unblemished ; and in other varieties, where the foliage appears in advance of the flowers, leaf tips were often blotched when there was not a single blind bud in the sample. It became evident from these gross tests that to avoid the varietal factor in the effect of treatment and to reduce the chances of flower injury it would be necessary to make the treatment under the most favorable conditions. These would include limiting it to the shortest feasible period, defining the optimum season for treatment, and ob- taining a working knowledge of the physical and mechanical factors affecting this optimum season. To study these points, a number of experimental series of tests were performed which will be discussed in the following pages. TOLERANCE OF BULBS TO TEMPERATURES ABOVE AND BELOW THE STANDARD To determine the tolerance of bulbs to temperatures above the selected standard of 110° to 111° F., bulbs of two varieties, Victoria and Emperor, were treated for 4 hours at 110°, 111°, 112°, 113°, 114°, and 115° on August 29-30, believed to be an optimum treating date. After treatments at temperatures of 110°, 111°, and 112° the flowers produced were of the same quality, but in the samples treated at temperatures above these they were definitely stunted and of slightly poorer qmility. The results of the tests are smnmarized in table 9.

TABLE 9.—Effect of -j-hoiir exposures at temperatures between 110° and 115° F. on the flowering of narcissus hulhs [24-bulb samples]

Victoria Emperor

Temperature (^J'\) Condi- Condi- Grade of Grade of Flowers tion of P'iowers flowers ' tion of flowers 1 foliage foliage

Number Number (2) . . 23 1 Normaí. 46 1-2 Normal. 110 21 2 ...do 48 3 Do. 111 .. 25 2 ...do 41 3 Do. 112 .. .- 23 2 ...do..-.. 37 3 Do. 24 3 Stunted. 28 3 Stunted. 19 3 ...do... 39 3 Do. 21 3 -.do 30 3 Do. 1 1 For system of (lower grades see table 7. 2 Untreated check. Several tests were also made of the tolerance of bulbs to temperatures of 106° and 108° F. These were included in a series, discussed later, conducted to observe the seasonal effect as well as for comparison between the different temperatures. . , , ,, The experiments demonstrated that the tolerance of the bulbs to a treatment of 8 hours at 106° F. was about the same as to a treatment of 2 hours at 110° to 111° (table 10) and that the treatments at 108° for 6 hours (table 10) were only slightly more severe in their effect, which was noticeable only at the less optimum treating seasons. It 22 TECHNICAL BULLETIN 6 7 2, IT. S. DEPT. OF AGRICULTURE would therefore seem of no advantage to use the lower temperatures, since the increased exposures necessary for insect control at these points (tables 2 and 4) would allow for no additional margin of tolerance. The period necessary for insect control at 110° to 111° was short enough to be convenient, and although higher temperatures required shorter durations, the plant tolerance decreased as the temperature was increased, therefore the standard of 110° to 111°, selected on the basis of previous thermal studies with hot water, was chosen as the best point at which to continue studies of plant tolerance.

OPTIMUM SEASON FOR TREATING NARCISSUS BULBS INTENDED FOR FORCING Realizing that vapor-heat treatment of narcissus bulbs might cause modifications of or injury to the resulting flowers, or complete blindness, if not done under optimum conditions, the relation of the season of treatment to such effects was studied. For this purpose samples selected from a common stock were handled identically throughout the storage season except for the date of treatment. In 5 series a sample was treated each week, and in 20 series the treatments were 2 weeks apart. Several varieties and types were represented and comparisons were made between the different treatment durations and the different temperatures. All treatment durations were exclusive of the approach period, which ranged from % to 1 hour. Tlie data of these series are presented in table 10.

TABLE 10.—Seasonal effect of vapor-heat treatment on the flowering of narcissus bulbs [24-bulb samples] TREATED 4 HOURS AT IIO"-!!!" F., 1931-32

Average Length of Flowers Blind buds Condition Variety and date of treatment storage grade i of produced flowers j)roduced of foliage

King Alfred; Days Number Number (') - 23 1.00 0 Normal. (>) 26 1.00 0 Do. July 2 -. 16 7.25 0 Do. July9 -- 23 2.26 0 Do. July 16-- 23 3.47 0 Do. July 23.. 24 2.95 0 Do. July 30- - 24 2.87 0 Do. Aug. 6... 25 2.40 0 Do. Aug. I3-. 24 2.41 0 Do. Aug. 20- 26 1.44 0 Do. Aug. 27.. 25 1.56 0 Do. Sept. 3-, 24 1.79 0 Do. Sept.10. 15 2.40 9 Do. Sept. 17- 18 2.26 6 Do. Sept. 24_ 24 2.04 0 Do. Oct. 1... 11 2.27 14 Blotched. victoria; (!) 23 1.00 0 Normal. m 23 1.00 0 Do. June 18-. 20 6.46 1 Do. June 25.- 22 6.0O 0 Do. July 2 -. 23 4.86 1 Do. July9 .. 22 2.40 0 Do. July 16-. 23 2.82 0 Do July 23-. 20 2.40 0 Do July 30.. 23 2.0O 0 Do. Aug. 6--- 23 2.00 0 Do. Aug. 13-- 20 2.0O Do. Aug. 20-. 24 1.58 Do. Aug. 27- 22 2.00 Do. Sept. 3-- 23 1.5« Do. See footnotes at end of table. VAPOR-HKAT TREATMENT FOR NARCISSUS BULB PESTS 23

TABLE 10.—Seasonal effect of vapor-heat treatment on the flowering of narcissus bulbs—Continued TREATED 4 HOURS AT UO"-!!!" F., I931-32-Contmued

Average Variety and dato of treatment Length of Flowers Blind buds Condition storage produced grade of flowers produced of foliage

Victoria—Continued. Days Nuviber Number Sept. 10--. 8.5 21 1.83 0 Normal. Sept. 17-- --- 92 23 1.09 0 1)0. Sept. 24-- -.- 99 20 1.4Ü 3 Do. Oct. 1 108 1 2.00 20 Do. Poeticus ornatus: (.') 21 l.OU 0 Do. {■) 24 1.00 0 Do. July 23.- 6 2.00 0 Do. July 30 21 2.23 Ü Do. Aug. 6 22 2.70 Ü Do. Aug. 13 22 2.13 2 Do. Aug. 20 17 1.94 0 Do. Aug. 27 _. 23 2.04 0 Do. Sept. 3--- 22 1.81 0 Do. Sept. 10-- -.- 21 1.67 0 Do. Sept. 17 15 1.80 3 Do. Sept. 24 18 2.33 0 Do. Oct. 1 2.00 0 Do.

TREATED FOR 3 HOURS AT 110°-111° F., 1932-33

King Alfred: (1) 1.00 0 Normal. (>) 1.00 u Do. July 13.. 3.13 1 Do. July 20.. 3.45 0 Do. July 27.. 2.87 0 Do. Aug. 3... 3.47 1 Do. Aug. 10.. 2.95 1 Do. -\ug. 17.. 2.91 II Blotched Aug. 24.. 3.00 K Do. Aug. 31.. 2.50 11 Do. Sept. 7-. 2.18 13 Do. Sept. 14. 2.44 0 Do. Sept. 21- 2.76 19 Do. Sept. 28, 2.31 6 Do. Victoria: (■) 1.00 0 Normal. (') - 1.04 0 Do. July 13 3. 3.42 1 Do. July 20.. 2.46 0 Do. July 27.. 1.82 II Do. Aug. 3... 2.00 0 Do. Aug. 10.. 1.41 0 Do. Aug. 17.. 1.37 0 Do. Aug. 24.. 1.30 2 Do. Aug. 31.. 1.94 7 Do. Sept. 7.. 1.04 1 Do. Sept. 14.. 1.19 1 Do. Sept. 21.. 1.18 1 Do. Sept. 28.. 1.26 3 Do.

TREATED FOR 2 HOURS AT llO'-lir F., 1932-33

Oolden Spur: (!, *) 17 1.05 0 Mosaic. July 13 --- 38 23 1.86 0 Do. July27 - - 82 24 1.37 0 Do. Aug 10 - «0 M8 1.61 0 Do. Aug 24 80 s 18 1.60 3 Do. Sept 7 ... - 94 23 1.62 0 Do. Sept 21 - 108 s 19 1.37 1 Do. »20 1.00 0 Normal. '"'T-r.-.- 38" «20 3.60 0 Do. 52 •18 3.33 0 Do. Aug 10 . 6B • 10 2.87 0 Do. Aug 24 80 M7 2.82 0 Do. Sept 7 94 i 14 2.67 0 Blotched. Sept. 21 108 ■ 18 2. 56 0 Do. See footnotes at end of table. 24 TECHNICAL BULLETIN 6 7 2, XJ. S. DEPT. OF AGRICULTURE

TABLE lO.^Seasonal effect of vapor-heat treatment on the flowering of narcissus bulbs—Continued TREATED FOR 2 HOURS AT 110°-111° F., 1932-33—Continued

Average Length of Flowers Blind buds Condition Variety and date of treatment grade of produced of foliage storage produced flowers

Number Bernardino: Day) Number 16 1.93 4 Normal. (•)- - 17 1.11 7 Do. (>) 6 Do. July 27.. 16 2.43 2U 1.35 0 Do. Aug. lU.. 1.41 Do. AUK. 24.. 17 13 1.53 Blotched. Sept. 7.. Do. Sept. 21. 3 2.66 Emperor: 24 1.20 Normal. (.') 21 1.1,0 Do. (1) Do. July 27.. 23 1.34 Aug. 10.. 24 1.16 Po. Aug. 24.. 24 1 16 Do. Sept. 7-. 23 1.13 Blotched. Sept. 21- 21 1.04 Do.

TREATED FOR 3 HOURS AT 110°-111°F., 1922-33

Golden Spur: (!, ') 17 1.06 0 Mosaic. July 13... 24 2.16 0 Do. July 27... 23 1.82 (1 Do. Aug. 10... 19 1.63 4 Do. Aug. 24--- 19 1.63 4 Do. Sept. 7... 94 19 1.42 3 Do. Sept. 21-- 108 17 1.68 4 Do. Beppy: (>) '20 1.00 0 Normal. July 13..- 38 '13 5.0O 0 Do. July27--. 52 116 4.87 0 Do. Aug. 10--- 66 '20 4.16 0 Do. Aug. 24... 80 Í 17 3.29 0 Do. Sept. 7--- 94 1 16 2.93 0 Blotched Sept. 21.. 108 '18 2.06 0 Do. Bernardino: (■) 15 1.93 4 Normal. (■) 17 1.11 7 Do. July 27... 12 3.25 7 Do. Aug. 10-- IS 1.83 0 Do. .\.ug. 24-.- 11 1.46 11 Do. Sept. 7... 7 2.20 11 Blotched Sept. 21-- 0 19 Do. Eraperor: (■) 24 1.20 0 Normal. (>) 21 1.00 0 Do. July 27... 2:1 2.60 0 Do. Aug. 10... 23 1.60 0 Do. Aug. 24... 24 1.66 0 Do. Sept. 7... ■a 1.17 0 Blotched Sept. 21-- 22 1.60 0 Do.

TREATED FOR 4 HOURS AT 108° F., 1932-33

Golden Spur: ('.') 17 1.06 0 Mosaic. July 14 23 2.26 0 Do. July 28...- 20 1,60 3 Do. Aug. 11 ... 21 1.71 1 Do. Aug. 25 21 1.85 3 Do. Sept. 8 '17 1.47 3 Do. Sept. 22... '13 1.64 6 Do. Beppy: {>) •20 1.00 0 Normal. July 14..-- 39 '18 4.88 0 Do. July 28.... 63 '18 3.50 0 Do. Aug. 11..-- 67 '16 3.25 0 Do. Aug. 2.5... 81 '12 2.83 0 Do. Sept. 8 96 • 19 2.67 0 Blotched Sept. 22... 109 22 2.63 0 Do. S^e footnotes at end of table. VAPOR-HEAT TREATMENT FOR NARCISSUS BULB PESTS 25

TABLE 10.—Seasonal effect of vapor-heat treatment on the flowering of narcissus bulbs—Continued

TREATED FOR 4 HOURS AT 108° F., 1932-33—Continued

Length of Flowers Average Blind buds Condition Variety and date of treatment storage grade of produced of foliage produced flowers

Bernardino: Days Number Number m - 15 1.93 4 Normal. (>)- n 1.11 7 Do. July 28.. 13 3.07 8 Do. Aug. 11.- 22 1.90 1 Do. Aug. 25.- 19 1.84 3 Do. Sept. 8.- 13 1.84 9 Do. Sept. 22. 1.40 16 Blotched. Emperor: 1.20 0 Normal. 8: 1.00 0 Do. July 28.. 1.61 0 Do. Aug. 11-- 1.35 0 Do. AUR. 25.- 1.91 0 Do. Sept. 8.. 1.45 0 Do. .Sept. 22 . 1.23 0 Blotched.

TREATED FOR 6 HOURS AT 108° F., 1932-33

Qolden Spur: (',') 17 1.05 0 Mosaic. July 14... 39 24 2.29 0 Do. July28..- 53 «18 2.10 (1 Do. Aug. 11--- 67 19 1.78 1 Do. Aug. 25... 81 20 1.75 1 Do. Sept. 8... 95 fi 2.66 4 Do. ■Sept. 22.. 109 16 1.68 5 Do. Beppy: (>) (20 1.00 0 Normal. July 14... 39 M8 5.05 0 Do. July 28.-- 53 Î20 4.70 0 Do. Aag. 11... 67 s 16 3.75 0 Do. Aug. 25... 81 S20 2.95 0 Do. Sept. 8... 95 ! 18 2.38 0 Blotched. Sept. 22,. 109 21 2.04 Ü Do. Bernardino: 15 1.93 4 Normal. (■) 7 (1) 17 1.11 Do. July 28... 16 3.12 4 Do. Aug. 11.-. 19 2.15 1 Do. Auf!. 25.-- 15 1.26 6 Do. Sept. 8..- 10 1.60 1(1 Blotched Sept. 22.. 0 16 Do. Emperor: (") 24 1.20 0 Normal. (")-. ?I 1.00 (1 Do. July 28-. 23 3.08 0 Do. Aug. 11... 22 1.77 n Do. Aug. 26.-. ■a 1.21 0 Blotched .Sept. 8... 23 1.26 n Do. Sept. 22.. 23 1.17 0 Do.

TREATED FOR 8 HOURS AT 106° F., 1932-33

Qolden Spur: 17 1.05 n Mosaic. (',') - n 1.77 1 Do. July 22 1 Do. Aug. 5 - 23 1.47 114 1.71 4 Do. Aug. 19 3 Do. Sept. 1 - 18 1.66 20 1.80 2 Do. Sept. 16 - 3 Do. Sept. 30 19 1.26 Beppy: 120 1.00 0 Normal. (!) - 21 3.85 II Do. July 22 - '20 3.05 0 Do. Aug. 5 -. - 0 Do. Aug. 19 t19 2.68 «20 2.80 0 Do. Sept. 1 «19 2.31 0 B'otched Sept. 16 1.64 0 Do. Sept. 30.. • 17 See footnotes at end of table.

107718°—.S9- 26 TECHNICAL BULLETIN 6 7 2, U. S. DEPT. OF AGRICULTURE

TABLE lO.Seasonal effect of vapor-heat treatment on the flowering of narcissus bulbs—Continued TEEATED FOR 8 HOURS AT 10ti° F., 1932-33—Continued

.\verage Length of Flowers Blind buds Condition Variety and date of treatment grade of produced of foliage storage produced flowers

Xumber Bernardino: Days dumber 15 1.93 4 Normal. (') - 17 1.11 7 Do. (') - 0 Do. Aug. 5.-. 21 2. ,52 21 1.33 0 Do. Aupr. 19.. 7 Do. Sept. 1.. 14 1.14 0 23 Blotched. Sept. 16- Do. Sept. 30. 1 1.00 21 Emperor: 24 1.20 0 Normal. «-- 21 1.00 0 Do. (')-. 0 Do. July 2-2.. 19 2.47 22 1.81 0 Do. Aug. 5... Blotched. Aug. 19.. 24 2.0O 0 Sept. 1-- 21 1.52 1 Do. Pont. 1«. 23 1.26 0 Do. Do. Sept. JO, 22 1.31 0

1 For system of flower grades see table 7. » No treatment. ■ Sample contained only 20 bulbs. ' Sample contained only 18 bulbs. ,, ,. ,t ' Reduction in quantity of flowers probably due m part to small bulbs used. From these experimental series it was determined that the optimum treating season from a forcing standpoint came at midseason, following tlie time when drying had become well advanced but before the new growth stimulation occurred. In general the first half of August appears to be the most favorable season in the Pacific Northwest, assuming that the bulbs are dug at normal season and are reasonably well dried. This is based on the fact that in all of the series good results were consistently obtained from bulbs treated during that period. This does not mean, however, that treatments at other periods did not result favorably. The date of treatment cannot be considered as the only determining factor, for that of the degree of drying is very important. There is also the factor of varietal difi'erence, whether of early- or late-flowering characteristics. In instances where the bulbs were well cured, successful flowering occurred in samples treated between the middle of July and the middle of September, but in seasons when only poorly dried bulbs were available the period during which treatments were made that produced good flowers was much more limited. This is well illustrated by a comparison of the results given in table 10. The first division of the table presents the flowering of King Alfred and Victoria bulbs treated in a season when weather conditions were favorable for thorough drying and the period of successful treating was quite extended. The second division presents the flowering of the same two varieties but in another year when the bulbs were poorly dried owing to unfavorable weather conditions. The season of successful treating was quite limited in this instance. Bulbs harvested early did not enter a favorable season for treating much before those dug normally. In the Pacific Northwest it is common practice to do some harvesting of early varieties in June and extend the digging operations throughout July. These studies indi- VAPOR-HEAT TREATMENT FOR NARCISSUS BULB PESTS 27 cate the advisability of a longer drying period for early-dug bulbs than for those left in the ground until later, probably a month or more for Jime-harvested bulbs and at least 3 weeks for July-harvested ones. If curing conditions are not of the best, a month or more would be advisable between digging and treating of the later types. It would not be good policy to treat any bulbs intended for forcing after the beginning of September, for the chances of causing blind buds are greatly increased in late-season treatments.

EFFECT OF DURATION OF TREATMENT ON FLOWERING In the large-quantity treatments it was frequently observed that samples of bulbs treated at the same time differed in the flowering results. The only logical reason for this effect appeared to be the difference in the length of time that the bulbs were subjected to the treatment temperature, owing to their locations in the treating room. This phenomenon was particularly evident in the field cultures, where portions of rows representing individual trays of bulbs had flowers decidedly different from those of other areas. Differences in flowering observed between separate stocks seemed to have been associated with the degree of drying. In the experimental work bulbs were treated for several durations in order to determine the influence of this factor. Other divisions of table 10 present data of the comparison of 2- and 3-hour durations at 110° to 111 ° F. and 4- and 6-hour durations at 108°. In the variety Golden Spur no particular differences were evident between the midseason treatments of 2 and 3 hours at 110° to 111°, biit in the series as a whole the longer duration produced a slight detrimental effect, particularly in the increased number of blind buds. In treatments of the variety Beppy the 3-hour durations were distinctly more detrimental than the 2-hour treatments at 110° to 111° throughout the whole season. The variety Bernardino was not affected by the difference in duration at midseason but the 3-hour duration for the series as a whole did not give quite so good results as the 2-hour treatment. No appreciable differences between the 2- and 3-hour treatment at 110° to 111° were observed in the variety Emperor. At 108° F. the variety Golden Spur responded almost similarly to 4- and 6-hour treatments, except that in the later treatments for 6 hours more blind buds appeared than in the 4-hour samples. In the variety Beppy at this temperature httle differences were evident between the 4- and 6-hour treatments. The longer treatment duration affected the variety Bernardino a httle more than did the shorter period. In the variety Emperor the difference in treatment duration at 108° caused no effect. , »,, , , ,i In table 10 data are presented on the flowering of King Alfred bulbs treated for 4 hours at 110° to 111° F., and similar data are given for 3-hour treatments at the same temperature. The two series of treatments were made in different years, hence are not directly comparable; nevertheless a comparison of the two groups of data shows that the 4-hour-treatment period was more favorable than that for 3 hours. In this case the duration of treatment was not considered the responsible factor, but rather the fact that the bulbs did not represent the same type of curing. Those that were treated for 3 hours were not so thoroughly dried as were those of the other series. 28 TECHNICAL BULLETIN 6 7 2, U. S. DEPT. OF AGRICULTURE

To determine the effect of extended durations, Victoria bulbs were treated for 4-, 6-, 8-, 10-, and 12-hour periods at 110° to HI F. The resulting flowers were of equally good quality and no reduction in the number of blooms was caused by any of the treatments, llie principal efïect in all the treated samples was the advancement of the date of blooming in the reverse order of the length of treatment. Ihe absence of unfavorable results in this series was due to tlie use of well- dried bulbs and treating them at the most favorable season. The results of this series are given in table 11. The general conclusion from this group of experiments is that duration of treatment in itself is not of particular consequence, but the associated factors of drying and season of treatment influence the results to such a degree that it is necessary in the treatment of bulbs intended for forcing to limit the treatment duration in order to mini- mize the effects of these factors. It appears that with durations of less than 4 hours at 110° to 111° F. the influence of the associated factors is considerably reduced. Since \}i hours duration gives the necessary control effect for those pests that would be involved, it is essential only that sufficient time be added to that period to com- pensate for variations that might occur in the mechanical operation of treating. T\Bi-E U.—Flowering of Victoria bulbs treated for different durations at 110° to 111° F., 1931-3^ [24 bulb samples]

Flowers Orade i Condi- Flowers Grade Condi- Duration of treat- Duration of treat- tion of pro- of tion of ment (hour.s) pro- of ment (hours) duœd flowers foliage duced flowers ' foliage

Number \umber Number Number 2 (■) -- 24 1 Normal. 8 - 23 24 2 Do. lU 24 2 Do. 0 24 2 Do. 12 23 2 Do.

' For system of flower grades see table 7. 3 No treatment.

COMPARATIVE TOLERANCE OF NARCISSUS VARIETIES In experimental series previously discussed the desirability of a 2 hour treatment at 110° to 111° F. was indicated for bulbs intended for forcing. To obtain further inf jrmation on the tolerance to this duration by narcissus generally, a number of the more common commercial varieties were treated when the bulbs were apparently well cured. Tiie following types were represented: Yellow trumpets, white trumpets, bicolor trumpets, incomparabilis, barrii, jonquilla hybrids, poetaz, polyanthus, poeticus, double, and tazetta. All the trumpet types seemed to be very tolerant to this treatment with the exception of King Alfred, which was modified from a flower with a typical even roll at the trumpet margin to one with irregular margin of the flare type similar to Tresserve or Minister Talma. Bicolor trumpets showed only inconsequential evidences of treatments, as did the incomparabilis, barrii, jonquilla hybrid, poeticus, and double groups. There is no reason to believe that the leedsii varieties would not react favorably, for they are close to the barrii and incomparabilis in form, but since no varieties of this group were VAPOR-HEAT TREATMENT FOR NARCISSUS BULB PESTS 29 available at the time, definite tests could not be made. The results with the poetaz varieties were variable, and the polyanthus and tazetta types reacted unfavorably, These, and also the poeticus

^#fj* ^^ ^'

■■■'^' KM' ^m ^^^^^^Ê^^^^^Êm " f 1

^^^^H ^^^^^^^^^B 1 CHECK ^^1 «e«

■i # . I ■^" ils"''* K" ■ t ' ' 1 ■

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FIGURE 13—Flowering of narcissus bulbs given the vapor-heat treatment for 2 hours at 110° to 111° F. Variety Beppy, bicolor-trumpet type. varieties, evidently require very early treatment in comparison to the daffodil types, on account of their shorter period of dormancy. Chinese sacred liles and Paperwhite narcissus are not grown in Wasliington or northern Oregon, but were included in these tests because they are produced on the west coast in regions farther south. More tests are necessary with these varieties. 30 TECHNICAL lU'LLF.TIX 072, U. S. DEPT. OF ACRICULTURB

FicaiiiE 14.—Flowering of narcissus bulbs given the vapor-heat treatment for 2 hours at 110° to 111° ¥. Variety Lucinius, inconiparaliilis type.

' ,^r.'

mnm^ x\^ FIGURE 15.-—Flowering of narcissus bulbs given the vapor-heat treatment for 2 hours at 1 10° to 111° F. Variety Diana Kasner, barrii type.

_ Photo

FIGURE 16.—Flowering of narcissus bulbs given the vapor-heat treatment for 2 hours at 110° to 111° F. Variety Laurens Kostcr, poetaz type.

FIGURE 17—Flowering of narcissus bulbs given the vapor-heat treatment for 2 hours at 110° to 111° F. Variety Laureate, poeticus type. 32 TECHNICAL BULLETIN 6 7 2, U. S. DEFT. OE AGKICULTUBE

TABLE 12.~Comparative flowering of varieties of narcissus following vapor-heat treatment of S hours at 110" to 111" F., 19S3-S4 [24-bulb samples]

Duration Flowers Grade Condition Variety of treat- pro- of of foliage ment ' duced flowers '

Hours Number Number 2 23 1-2 Blotched. Aerolite 0 23 1 Normal. 2 24 1 Blotched. Emperor 0 24 1 Normal. 2 23 1-2 Blotched. Golden Spur 0 24 1-3 Mosaic. 2 21 3-4 Blotched. King Alfred 0 20 1 Normal. 2 22 1-2 Do. Minister Talma... 0 24 1 Do. 2 23 1-2 Blotched. Pacific Spur 0 24 1 Normal. 2 24 1-2 Do Sir Francis Drake. 0 23 1 Do. 2 23 1-2 Blotched. The First 0 23 1 Normal. 2 24 1-3 Blotched. Tresserve 0 24 1 Normal. 2 22 1-2 Blotched- Livingstone 0 21 1 Normal 2 24 1-2 Do. Beppy 0 24 1 Do. 2 21 1-2 Blotched. G lory of Sassenheim 0 24 1 Normal. 2 23 1-2 Do. Spring Glory 0 19 1 Do. 2 22 1 Do, Victoria 0 24 1 Do. 2 23 1-2 Blotched. Lucinius 0 24 1 Normal. 2 24 1-2 Do. Sir Watkin 0 23 1 Do. Diana Kasner 2 23 1-2 Blotched. 0 23 1 Normal. Nannie Nunn 2 21 1-2 Do. 0 24 1-2 Do. Golden Scepter 2 23 2 Blotched, 0 23 1 Normal. Achelous 2 18 1-4 Blotched. 0 22 1-2 Normal. Laurens Koster.. 2 24 1-2 Do. 0 23 1 Do. Majestic 2 19 1-4 Blotched. 0 19 1 Normal. Orange Cup 2 10 1-5 Blotched. 0 22 1 Normal. Soleil d'Or (California)..., 2 21 4-6 Do. 0 24 1 Do. Soleil d'Or (Washington). 2 13 4-B Do. 0 21 1 Do. Laureate 2 14 1-2 Do. 0 13 Do. Twink. 2 23 Do. 0 23 Do. Chinese sacred lily (California). 2 21 4-6 Blotched. 0 22 1 Normal. Paperwhite (California) 2 5 3-5 Blotched. 0 21 1 Normal.

• Zeros in this column represent untreated check samples. = For system of flower grades see table 7, page 18.

PRACTICAL APPLICATION OF THE VAPOR-HEAT METHOD TO THE TREATMENT OF BULBS INTENDED FOR FORCING The commercial grower who desires to treat bulbs intended for forcmg purposes must consider several factors. To avoid uneven heating it is advisable to limit the load so that the approach period is reduced to Iji or 2 hours. Trials have indicated that trays should not be stacked more than three high to obtain this result. VAPOR-HEAT TREATMENT FOR NARCISSUS BULB PESTS 33

A minimum treatment duration of 2 hours at 110° to 111° F. will allow sufficient time for complete kill of insect and mite pests and for compensation of heating variations due to mechanical operation. In the Pacific Northwest the most favorable period for treating narcissus bulbs appears to be the first half of August, provided the bulbs are well cured. At least 3 weeks' curing should precede treatment. Recognition must be given to the difference in response by different varieties and types of narcissus. On account of growth characteristics poetaz, polyanthus, poeticus, and tazetta varieties must be treated before developmental response within them becomes stimu-

FiQDRE 18.—Flowering of narcissus bulbs given the vapor-heat treatment for 2 hours at 110° to 111° F. Variety Golden Scepter, junquilla hybrid type. lated. Because of its sensitivity, resulting in more or less flower modification, the variety King Alfred should be treated only when the several factors are most favorable. TREATMENTS OF BULBS INTENDED FOR FIELD PLANTING To determine the reactions of planting stocks to vapor-heat treatments three criteria have been used: (1) Increase of bulb weight in carefully controlled series of treatments during the storage season, (2) increase in bulb weight of samples representing large-quantity commercial treatments, and increase in quantity of complete stocks, and (3) observations of the performance of complete stocks as they were grown commercially. Over 1,000 tons of planting stock were treated under the supervision of the laboratory staff, and subsequent observations were made on general behavior and appearance in the field. Irregularities and variations that appeared in samples representing these stocks that were grown at the laboratory in weight-increase tests were easily understood when the particular treated stock was viewed as a whole. 34 TECHNICAL BULLETIN 6 7 2, U. S. PEPT. OF AGRICULTURE

Since the resulting flower quality was not a factor in treating planting stock, it was assumed that the favorable season at which treatment could be applied would be longer than in the case of forcmg stocks. For this reason serial tests were made to determine the efl^ect of seasonal change.

OPTIMUM SEASON FOR TREATING NARCISSUS INTENDED FOR BULB PRODUCTION To determine the seasonal limits witliin wliich narcissus bulbs might be given the vapor-heat treatment without detrimental effects on bulb increase it was necessary to compare treatments throughout the entire season of bulb storage. At first a 4-hour treatment at 110° to 111° F.

N n >ioo

5 50 \

2 9 16 23 30 6 13 20 27 3 10 17 24 I JULY AUGUST SEPTEMBER FIGURE 19.—Comparative weight increase of King Alfred narcissus bulbs, given the vapor-heat treatment for 4 hours at 110° to 111 ° F. at different dates during the storage season. C, Average weight increase of untreated checks. was selected as a standard. Later this was extended to 8 hours, as it became evident that the bulbs would tolerate that duration and that if the treatment was eventually adapted for nematode control it would require more than 4 hours for satisfactory results. Also, in order to emphasize the seasonal effect, 12,- 18-, and 24-hour durations were employed. In these series, increase in duration of treatment was accompanied by reductions in bulb tolerance. In the 4-hour treatments of the variety King Alfred the bulb increase was above that of the untreated checks e-xcept for the last treating date, October 1 (fig. 19). Similar results were obtained for the variety Victoria except for the first eighth, and last treatments (fig. 20). For the bulbs of Poeticus ornatus VAPOR-HKAT TREATMENT FOR NARCISSUS BULB PESTS 35

\ \ \ \ \ 150 ■ \ \ \ \ \ \ \ \ \ \ \ \ \ \ - \ - \ \ \ \ - c \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ IE 100 \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ \ \ \ \ \ \ \ \ \ \ \ N \ \ \ \ \ L 18 25 9 16 23 30 13 20 27 3 10 17 24 I JUNE JULY AUGUST SEPTEMBER FIGURE 20.—Comparative weight increase of Victoria narcissus bulbs given the vapor-heat treatment for 4 hours at 110° to 111° F. at different dates during the storage season. C, Average weight increase of untreated checks. 100

z Ü tr \ \ \ ui \ Q., \ \ \ \ \ \ \ \ ^ 50 - \ < \ \ lij \ \ \ \ \ \j \ o \ \ \ \ ._. c \ — \ — k \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 23 30 6 13 20 27 3 10 17 24 I JULY AUGUST SEPTEMBER FiGUHE 21.—Comparative weight increase of Poeticus ornatus narcissus bulbs given the vapor-heat treatment for 4 hours at 110° to 111° F. at different dates during the storage season. C, Average weight increase of untreated checks. 36 TECHNICAL BULLETIN 6 72, TT. S. DEPT. OF AGRICTILTURE

lOOi ^—

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13 20 27 3 10 17 24 31 7 14 21 28 JULY AUGUST SEPTEMBER FIGURE 22.—Comparative weight increase of King Alfred narcissus bulbs given the vapor-heat treatment for 8 hours at II0° to 111 ° F. at different dates during the storage season. C, Average weight increase of untreated checks.

100

oUJ (r UJ & UJ < 50 a:UJ o

13 20 27 10 17 24 31 7 14 21 28 J ULY AUGUST SEPTEMBER FIGURE 23.—Comparative weight increase of Victoria narcissus bulbs given the vapor-heat treatment for 8 hours at 110° to 111° F. at different dates during the storage season. C, Average weight increase of untreated checks. VAPOK-HEAT TREATMENT FOK NARCISSUS BULB PESTS 37 the best treating dates occurred from July 23 to September 17, inclu- sive. A decided drop in production occurred in the bulbs treated September 24 (fig. 21), due probably to the shorter dormant period of this variety.

\ \ c \ \ \ \ \ \ \ \ \ 50 ■ \ \ \ \ \ \ ■\ \ '\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ L N 18 I 15 29 12 26 JULY AUGUST SEPTEMBER FiouRE 24.—Comparative weight increase of King Alfred narcissus bulbs given the vapor-heat treatment for 12 hours at 110° to 111° F. at different dates during the storage season. C, Average weight increase of untreated checks.

100

50 18 I 15 29 12 26 JULY AUGUST SEPTEMBER FIGURE 25.—Comparative weight increase of Victoria narcissus bulbs given the vapor-heat treatment for 12 hours at 110° to 111° F. at different dates dunng the storage season. C, Average weight increase of untreated checks. 38 TECHNICAL BULLETIN 6 7 2, U. S. DEPT. OF AGKICULTURB

100

lli \ 2 50 - \ O \ p r-1 p- \ \ \ ■■\ \ \ \ P \ \ \ UJ \ ■^^ ^ \ tr \ UJ .... \ \ u

IS 15 29 12 26 JULY AUGUST SEPTEMBER FIGURE 26.—Comparative weight increase of King Alfred narcissus bulbs given the vapor-heat treatment for 18 hours at 110° to 111° F. at different dates during the storage season. C, Average weight increase of untreated checks.

11 1 ^1 ¥

18 15 12 26 JULY AUGUST SEPTEMBER FIGURE 27.- -Comparative weight increase of Victoria narcissus bulbs given the vapor-heat treatment for 18 hours at 110° to 111° F. at different dates during the storage season. C, Average weight increase of untreated checks. VAPOR-HEAT TREATMENT FOR NARCISSUS BULB PESTS 39

In the 8-hour series of King Alfred the weight increase of the bulbs shows definite reductions as compared with the checks after Septem- ber 14, but all treatments on and before that date were considered satisfactory (fig. 22). With the variety Victoria the majority of tests were above the checks in increase, although three were slightly and the last one considerably below (fig. 23). In the 4- and 8-hour series 53 of the 65 treated samples of all varieties showed more increase than the untreated checks. Seven of the twelve samples which did not grow as well as the checks were treated after September 17. This indicates less tolerance during the latter part of the storage season.

12 26 SEPTEMBER FIGURE 28.—Comparative weight increase of King Alfred narcissus bulbs g vc.i the vapor-heat treatment for 24 hours at 110° to 111° F at different datos during the storage season. C, Average weight increase of untreated checiss. In the 12-, 18-, and 24-hour tests with Kmg Alfred and Victoria (figs 24, 25, 26, 27, 28, 29), the effect of treatment apparently becomes more severe as the storage season advances. Treatments made m July and August at these extended durations were not particularly detrimental, but September treatments were distinctly severe. Based on these results, it is again evident that narcissus bulbs are most tolerant of vapor-heat treatment in the earlier portion of the storage ^^Ext'ended durations of treatment are not advisable in the latter part of the season from the standpoint of bulb tolerance but since these long treatments would be used only for nematode control, which is best effected early in the season, there is no need of subjectog bulbs to long exposures late in the season. The season of favorable tolerance is much longer for the shorter treatments, and exposures sufficient to^onïriîbdb fly larvae and mites could be safely used m any part of the season as long as the bulbs have not sprouted. 40 TECHNICAL BULLETIN 6 7 2, U. S. DEPT. OF AGBICULTUBE

Since in the 4- and 8-hour series 54 samples had increases in weight equal to or greater than those of the untreated checks while only 11 had increases less than those of the checks, and furthermore, since in all treatments made during the favorable season the increase was decidedly more than that of untreated bulbs, it would seem that the treat-

■ 00 \ \ \ \ \ \ \ \ 50 - \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 0 \ \ \ \ \ \ \

18 12 26 JULY SEPTEMBER FIGURE 29.—Comparative weight increase of Victoria narcissus bulbs given the vapor-heat treatment for 24 hours at 110° to 111° F. at different dates during the storage season. C, Average weight increase of untreated checks. rnent was of considerable benefit from the standpoint of bulb production.

PERFORMANCE OF COMMERCIAL STOCKS FOLLOWING VAPOR-HEAT TREATMENT During the years from 1930 to 1934 over 1,000 tons of planting stocks representing 166 varieties were treated by growers of western Washmgton under the direct supervision of the laboratory staff. These stocks received regular commercial handling, and their development was carefully observed by both the author and the growers The opinions of the latter were solicited because of their practical viewpoint. No variety could be classed as not tolerant of vapor- heat treatment, although there were instances of fairly severe damage to limited quantities of stock for which the lateness of the treatment was considered responsible. The more serious cases involved bulbs which had been treated after they had sprouted. Plgure 30 shows a stock of the variety Emperor at blooming time (April 13) which was given a vapor-heat treatment the previous year on September 5 for a minimum 4-hour treatment at 110° to 111° F VAPOÜ-HKAT TltKAT.MKXT I'OK XAUCISSITS nULI! PKSTS 41

l'^HiURE 30.—A commercial stock of Kmperor narcissus in bloom following a vapor-heat treatment of 4 hours at 110° to 111° F. (Photograph through courtesy of F. P. McWhorter.) Field observations were made on the following varieties treated by vapor heat: Yellow trumpets.—Aerolite, Alasnam, Bassanio, Cervantes, Colorable, Diotima, Dreadnaught, Duchanel, Emperor, Giant Killer, Golden Spur, Golden Princeps, King Alfred, Liberty, Minister Talma, Moonlight, Mustapha, Olympia, Pacific Spur, Robert Sydenham, Sir Francis Drake, The First, Tresserve, Van Waveren's Giant, Warwick. White trumpets.—Almee, Jungfrau, La Vestale, Mrs. Ernst H. Krelage, President Roosevelt, Sir Ernest Shackleton. Bicolor trumpets.—Átropos, Beppy, Cennedy, Empress, Glory of Sassenheim, Golden Beauty, Jefta, Lovenest, Marie, Martha, Robert Lee, Silver Spur, Spring Glory, Victoria, Weardale Perfection. Incomparabilis.—Arizona, Balisand, Bernardino, Carmencita, Croesus, Dick Wellband, Franciscus Drake, Gallipoli, Gladiator, Great Warley, Helios, Jefferson Davis, John Evelyn, Loudspeaker, Lucifer, Lucinius, Marigold, Mi-Careme, Michigan, Milford Haven, Red Cross, Salembo, Shchcrasade, Sir Watkin, Solfa- tare, Stella Tid Pratt, Tagore, Tampa, Whitewell, Ycka. Barrii.—Alcibiades, Alcida, Anna Croft, Barrii conspicuus. Baths ilame, Diana Kasner, Dosoris, Firebrand, Firetail, Fleur, Freifrau von Friesen, í rau Margarethe Hohmann, Gionesius, Lady Moore, Livingstone, Masterpiece, Mrs. Barclay, Nannie Nunn, Nursemaid, Red Chief, Seagull, Sunrise, Will Scarlett. ieedsn.—Arion, Emtiire, Evangeline, Gertie Millar, Hera, Lord Kitchener, May Blossom, Mrs. Nette O'Melvcny, Mrs. R. 0. Backhouse, Queen of the North, Silver Star, White Lady, White Queen. Triandrus hybrids.—Agnes Harvey, Moonshine, Pearly Queen. Cyclamineus hybrid.—February Gold. Jonquilla hybrids.—Battercnp, Campernelli Rugulosns, Campcrnclli I'lora Plena, Campernelli Orange Queen, Campernelli Giganteus, Chrysolite, General Pershing, Golden Sceptre, Lady Hillingdon, Remulus, TuUus Hostihus. Tazetta hybrid (triandrus group).—Thalia. . Tazetta hybrids (poetaz group).—Admiration, Achelous, Asa, Aspasia, Boer- haave, Elvira, Frans Hals, Glorious, Laurens Koster, Majestic, Mrs. Asquith. Orange Cup, Orient, Raphael, Sycamore. Tazetta hybrid (polyanthus group).—Grand boleil d Ur. 42 TECHNICAL BULLETIN 6 5 U. S. J1EPT. or ACiRICULTUUE

Podicus.—Dante, Eagle, Edwina, Juliet, Laureate, Poeiicua ornatus, Queen of England, Snow King, Socrates. Doubles.—Albus Plenus Odoratus, Argent, Daphne, Golden Phoenix, Holland's Glory, Livia, Mary Copeland, Moulin Rouge, Orange Phoenix, Perfection, Sulphur Phoenix, Telamonius plenus, Twink. To obtain specific information on the effect of large-quantity treatments on bulb increase, samples of bulbs of uniform size were selected at random from the treated stocks and were grown in comparison with untreated bulbs representing the same stocks. The results were determined by comparing the increase in weight of the treated and untreated samples, which was done by weigliiiig bulbs just prior to l)lanting and again after they were harvested and thoroughly dried. Tlie results of the 77 tests are shown in table 13, in which the bulb iiicrciise of the treated samples is classified as (1) greater than that of their checks, (2) equal to tiie checks, and (3) less than the checks. If tlie difl'erence between treatment and check was less than 5 percent they were considered equal. In 44 tests the increase was greater that that of their checks, in 15 tests it was equal, and in 18 it was less.

TABLE 13.— Weight increase of narcissus bulb samples representing large-quant it i/ treatments (minimum treatment duration 4 hours at 110° to 111° F) 19S0~Si 1931 32.

Increase Variety Date Weight treated increase classifi- Remarlis cation 1

Percent Aug. 27 92 Equal (') 93 Aug. 30 49 Less (') 82 Sept. 4 38 Equal J (') 43 \Sept. 6 71 Greater... (') 62 Sept. 8 24 Less .... ICultural factor. General field growth (') 102 Sept. 16 73 Equal 1') 74 Empross /Aug. 20 100 Less 126 Aug. 17 18 Less (') 04 JBoth samples damaged by basal rot. Sept. 16 69 Equal (') 64 Olory of Sassenheim Sept. 22 67 Greater... (') 31 Sept. 24 86 Greater... « 66 Aug. 28 68 Greater... (>) 21 Golden Beauty Sept. 16 130 Equal (■) 131 July 29 74 Equal (') 72 Aug. 4 36 Less 46 iBasal rot present in both samples. Aug. 23 68 Greater... (') 42 Aug. 26 81 Greater... (') 36 Oolden Spur Aug. 25 126 Greater... (') 68 Aug. 26 101 Greater... m 02 Aug. 27 82 Greater... m 67 Sept. 15 77 Less Treatment too late. 1 112 S.'p footnotes at end of table. VAI'Olí-lIKAT TIUOATMENT FOR NARCISSUS lUILl! TESTS 43

TABLE 13.—Weight increase of narcissus bulb samples representing large-quantity treatments {minimum treatment duration 4 hours at 110° to 111° F.), 1930-31. í9S/-3á—Continued

Date Weight Increase Variety treated classifi- Kemarks increase cation

Percent Aug. 12 1113 I-ess... _. m 118 Aug. 13 102 (lreater,__ (') 13« Aug. 17 02 ess _ Cultural faclor—sanily .'^pot in bed. (') 83 Aug. 2(1 104 ) 00 Sept. 9 138 Greater... (') 75 Sept. 16 141 Greater... (!) 87 See fool notes at end of table. 44 TECHNICAL BULLETIN 6 7 2, IT. S. DEM. OF AGRICULTURE

IVBLE 13.—Weight increase of narcissus bulb samples re-presenting large-quantili/ treatments (minimum treatment duration 4 hours at 110° to 111° F.), 19S0-81. lOSl-SS—Continued

Incrca-^c Dato Weight Variety classifi- Keraarks treated increase cation

Percent Aug. 3 83 Greater m 77 Sei)l. 11 104 Greater I'tlantoniu.t />/i-7if/.* (Vun Sioii) (') 81 Sept. 1() 94 Greater (■') 26 Sept. 2(1 82 Greater . (') 36 .iUR. 17 75 Greater {') 48 Sept. 10 fil Greater (') 15 Sept. 12 83 Greater m 60 Sept. 18 88 Greater (') 36 .Sept. la 101 Greater I (') 54 Sept. 22 36 Equal.. \'HU Wftvereii (liant , (') 33 .^UE. 1 41 Equal-. (') 46 Aug. 4 142 Greater m 107 Aug. 5 81 Greater 0) 52 Aug. fi 27 Greater (') 21 Aug. 311 49 Greater P) 40 Sept. 14 104 Equal., (') 102 Sept. LI 87 (greater. « 67 Sept. 20 62 Greater (') 13 Sept. 22 62 Greater m 41 Will Scarlett- f.Sept. 10 64 Greater (0 29

' Weight of treated bulbs in comparison to that of untreated bulbs, Variations under 5 percent are not considered. ' I'litreated check sample. l^articular attention to those tests in which there was an apparently detrimental effect revealed factors other than the treatment that were probably involved in the poor response. These factors were cultural conditions, variations within a load caused by a long approach period, treatment too late in the season, and the presence of basal rot. Com- parison with the field-grown stocks indicated that the experimental samples yielding below normal were not truly representative of the stocks as a whole. The general results of the field tests correspond with those of the experimental series. Stimulation of growth was distinctly evidenced in treatments made during the optimum season, and the late-season treatments demonstrated the lowered tolerance of the bulbs at that time. When the method of random sampling is used in studies such as these a certain measure of doubt arises as to whether the samples are truly representative of the effect on the stocks as a whole, and it is accordingly desirable to have accurate records of the effect of the treatment on entire stocks. Therefore records of the quantities of VArOH-HlCAÏ ÏRliATMENT l'Oll NARCISSUS BULB PESTS 45

bulbs planted and dug, made by one of the commercial growers in the Fuyallup Valley in western Washington in 1934, 1935, and 1936, were studied to determine the effect of treatment on the increase of entire stocks. It is the custom of this grower to treat one-half of his stocks each year, most of the treated bulbs receiving a 4-hour treatment at 110° to 111° F. It was possible by this means to obtain the percentages of increase of a number of large stocks of narcissus bulbs that had been given vapor-heat treatment in 1935. Unfortunately check lots could not be observed under such an arrangement, but in nearly all cases the records of increase of these stocks were available for the previous year when they did not receive any treatment. Sixteen out of twenty-one stocks with records for 1935 increased more in 1936 than in the previous year (table 14). Every lot of King Alfred showed better growth than in 1935 where records were available. While ail the bicolor varieties did not show increases above those of 1935, the differences were not enough in those that increased less than they did the previous year to indicate a detrimentiil effect from treatment. The varieties Minister Talma and Mrs. Ernst II. Krelage also had increases below those of 1935, but the increase obained was well within the range of normal growth. The remaining varieties, Tela- monius j)lenus, The First, Emperor, Achelous, and Sir Watkin, all increased more than in 1935.

TABLE 14.—Increase of commercially handled planting stocks of narcissus bulbs during the growing season of 1986 following vapor-heat treatment

Curing Trays Treatment 1935 in- period Increase duration at before crease * 110° to 111° treatment ' Planted Dug

Days Number Number Percent AcheIous_ _ - 25 48 85 77 Kmperor 12-14 211 377 79 fllory of Sossenheim 13-14 367 471 28 33 Oolden Beauty - 12-28 ISO 342 SO 72 KinK Alfred (Ai__ 30 406 740 82 14-19 284 496 74 ,55 Kins Alfred (B) 39 KiiiK Alfred (C) 15-2.') 564 986 75 13-32 326 508 S3 71 Kins Alfred (D) 47 KinK Alfred (E) 16-26 567 1,000 76 ('04 91 47 Kins; Alfred (F)--- 21-28 316 21-34 255 444 74 26 KInE Alfred ((!) 225 112 21 King Alfred (II) 22 106 14 41 71 73 39 KinR Alfred (I) 95 28 King Alfred (J) 14 74 14 366 528 44 Kinc Alfred (K) 1.52 34 Marie 12-31 97 14-17 723 1,134 67 Minister Talma 118 80 Mrs. Ernst H. Krelsge. 14 70 15 Iff! 248 64 Siher .Spur,, 730 40 Sir Watkin 21 420 13-32 416 617 43 Sjiring Olory -- 1,029 2.021 82 Telamonius plenm 1.5-29 14-23 697 1,373 .58 The First 600 790 43 Victoria 14-26

. The first figure shows the pretreatment drying period of most of the stock and the second the drying '^rTU:i'¡'¿2!Z^Qp"eLl ¡ncrea.ses during a season when n. treatment was given to hulhs. 5 8ometreatB

observations, with extra good conditions an increase of 75 to 100 percent often occurs. This criterion can be used also in interpreting the results of table 14. All bulbs were mechanically graded about 12 days after digging. The planting sizes from this grading were immediately treated before being stored until planting time. The salable sizes were later regraded, and planting sizes resulting from the second grading were accumulated until there were enough for a load in the vapor-heat treating room. After treatment these "regrades" were added to the regular planting stock, where their identity was lost during planting. In table 14 two figures are given in the third column, the first representing the pretreatment drying period of most of the stock and the second the drying period of the "regrade" lot. In the variety Telamonius plenus (Van Sion) a portion of the bulbs were treated for 8 hours at 110° to 111° F. and the large remainder for 4 hours at the same temperature, but the identity of the two lots was not maintained. Each tray contained about 65 poimds of bulbs, making about 31 trays per ton. During the spring of 1936 a close observation of the condition of foliage and flowers of these stocks was maintained by both the grower and the writer. In no instance was there foliage damage or any evident decrease from normal growth. In a few instances there was some reduction in flower quality, but aside from that in the variety Achelous, which received an 8-hour treatment, damage occurred usually on less than 1 percent of the flowers.

COMPARATIVE EFFECT ON BULB PRODUCTION OF TEMPERATURES OF 105°. 107°. AND no" TO nr F. FOR PROLONGED DURATIONS Although 110° to 111° F. has been generally used as a standard temperature, it was considered desirable to determine the effect of lower temperatures, at which it is necessary to use increased treat-

E 50

b^ k 12 HR. 18 HR, 24 HR. 12 HR 18 HR. 24 HR. 12 HR IS HR. 24 HR. 105° 107° iio-iir *iV/"^j "'"P'^'"^*'^^ ^''"' weight increase of narcissus bulbs, variety King . . .'JT''", * Í yapor-heat treatment for 12, 18, and 24 hours at 105^, 107°, and iiu to 111 Í. C, average weight increase of untreated clieclis. VAPOR-HKAT TREATMENT FOR NARCISSUS BULB PESTS 47 meiit durations to obtain equivalent toxicity. Samples of two varieties, King Alfred and Victoria, were treated 12, 18, and 24 hours at 105°, 107°, and 110° to 111° F., and were grown in the laboratory plot under normal field conditions. The comparison of the treatments is based on tlie weight increases of the bulbs. These are shown graph- ically in figures 31 and 32. In the variety King Alfred there was a noticeable lessening of tolerance as the temperature increased. In Victoria the increase was about the same at all three points, but the 105° and 107° treatments produced better foliage and more flowers than did the 110° to 111°

12 HR. 18 HR 24 HR. 12 HR. 18 HR. 24 HR. 12 HR. 18 HR. 24 HR. 105' 107° 110-111° FIGURE 32.—Comparative bulb weight increase of narcissus bulbs, variety Victoria, given the vapor-heat treatment for 12, 18, and 24 hours at 105°, 107°, and 110° to 111° F. C, average weight increase of untreated checks.

treatment, thus agreeing on a lesser scale with the reaction of King Alfred. It is evident that 105° is near the temperature point at which an extended treatment could be given without plant injury.

ACCUMULATIVE EFFECT OF CONSECUTIVE ANNUAL TREATMENTS A phase of interest to commercial growers is whether there might be an accumulative effect on a stock of bulbs when treated in successive years by vapor heat. To obtain information on this, lots of two varieties. King Alfred and Glory of Sassenheim, have been subjected to a 4-hour treatment at 110° to 111° F. each year smce 1930 and grown in comparison with an untreated check lot of each variety. Culls and fly-infested bulbs were removed from the stocks each year. The effect of treatment has been determined by comparing the percentages of weight increase. The results for 6 years are shown in figures 33

The second year of treatment was definitely not detrimental to bulb growth for King Alfred bulbs made decidedly better growth than their checks'and Glory of Sassenheim samples approximately the same 48 TECHNICAL BULLETIN 6 7 2, U. S. DEPÏ. OF AüllICULTURE growth as tlieir checks. The differences between check and treated samples following the third annual treatment was not great enough m either variety to be considered as caused by treatment. Following the fourth annual treatment both varieties had less increase for the treated samples than for the checks, but pathological conditions were probably the major factor responsible. During the spring months English fire (Botrytis polyblastis) was particularly prevalent and bulbs treated by vapor heat appeared more susceptible than untreated ones. Following the fifth annual treatment the treated lot of King Alfred bulbs increased appreciably less than its check, but in the Glory of Sassenheim the increase was in favor of the treated bulbs. Although

:I00 - \ \ \ \ \ \ \ \ \ pi \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^ \ \ \ \ \ \ \ \ \ \ TR CH. TR. CH. TR. CH. TR. CH. TR. CH. TR. CH. 1931 1932 1933 1934 1935 1936 FiGUKB 33.—Bulb-weight increase of King Alfred narcissus bulbs given consecutive animal vapor-heat treatments of 4 hours at 110° to 111° F. TH indicates the treated bulbs and CH the check lot. less than in the clieck, the increase of the treated King Alfred was considered as satisfactory. The increase the sixth year was the reverse of the previous season, untreated checks of King Alfred increasing less than the treated sample and treated bulbs of Glory of Sassenheini less than their check. As a result of these tests it is considered that bulbs may be treated in consecutive seasons without fear of detrimental effects.

COMBINATION OF VAPOR-HEAT TREATMENT WITH OTHER COMMONLY EMPLOYED BULB TREATMENTS Bulb glowers utilize fumigation with hydrocyanic acid gas quite generally to control larvae of bulb Hies, and furigicidal dips are used to prevent damage by basal rot. Observations were made where bulbs liad received combinations of each of these with vapor-heat treatment during the storage season. VAPOR-H EAT TRKATMENT FOR NARCISSUS BULB PESTS 49

VAPOR-HEAT TREATMENTS FOLLOWING FUMIGATION WITH HYDROCYANIC ACID GAS There, hnve boon a few occurrences in commercial liaiulling where fumigated bulbs were later given vapor-heat treatment. In one case there was a lapse of several weeks between the fumigation and the ensuing thermal treatment, and the stock of bulbs showed considerable injury to foliage the following spring. This was attributed to the stimulating effect of hydrocanic acid gas fumigation, it causing prema- ture leaf growth within the bulb which was not compatible with vapor-heat treatment. This effect was comparable to that of late- season treatment. In other cases when treatment immediately fol- lowed fumigation, it caused no injury to the resulting crop.

Í 50

TR. CH. TR. CH. TR. CH. TR. CH TR, CH. TR. CH. 1936 1931 1932 1933 1934 1935 FicuRE 34.—Bulb-weight increase of Glory of Sassenheim narcissus bulbs given consecutive annual vapor-heat treatments of 4 hours at 110 to 111 t. IK indicates tlic treated l)uU)S and CH the check lot.

COMBINATION OF VAPOR-HEAT TREATMENT WITH A CERESAN DIP Many growers dip planting stocks in a solution of Ceresan (2-perœnt ethyl mercury chloride) to prevent the occurrence of basal rot. llie results of tests made with the varieties Emperor and Victoria to determine whether Ceresan dips and vapor-heat treatment were compatible are presented in table 15. A n „„„ A 4-hour treatment at 110° to 111° F. was emp oyed A Ceresan din (1 pound to 8 gallons of water) was given one lot of each variety immediately preceding the vapor-heat treatment. A similar dip was used just before planting for one lot of each variety that had been vapor-heat treated, and also for an untreated lot (Ceresan check). Lots receiving vapor-heat treatment only were utilized to check the effect of the combinations, and bulbs receiving neither treatment nor dipping served as a general check. 50 TECHNICAL lUTLLKTIN G72, U. S. DEFT. OF AGRICULTUUK

TABLE 1,5.—Results of combining vapor-heat treatment (4 hours at HO"-!!!" F.) with a Ceresan dip as evidenced by bulb-weight increase

Emperor Victoria

Treatment Weight Weight Increase Weight Weight Increase planted dug planted dug

Ceresan dip before vapor-heat treat- Ounces Ounces Ounces Percent Ounces Ounces Ounces Percent 160 258 98 61 VO 158 82 108 Ceresaii dip after vapor-lieat treatment 157 262 106 67 73 144 68 89 183 271 108 66 79 142 63 80 Teresanonly 163 272 109 67 78 186 108 138 167 274 107 64 78 177 99 127

The tests with Emperor bulbs showed no particular differences bo- tween any of the combination treatments given, or the checks. The variety Victoria did not respond particularly well to the vapor-heat treatment, owing probably to the lateness of the season of treatment (September 15), but both samples that were dipped in Ceresan and vapor-heat-treated performed distinctly better than the bulbs that received vapor-heat treatment only. These tests demonstrate that there is no incompatability between vapor-heat treatment and a Ceresan dip of the strength indicated.

STIMULATION OF GROWTH OF NARCISSUS CAUSED BY VAPOR-HEAT TREATMENT Throughout all the experimental work on narcissus with vapor-heat treatment a general stimulation of growth has been more or less evident. This is verified by the opinions of commercial growers who have treated their stocks. Such stimulation is apart from that which often results from the treatment of bulbs infested with the bulb scale mite. In general, treatment of properly cured bulbs should result in vigorous growth and a bulb increase above normal. Certain instances have been noted where vapor-heat treatment caused marked stimulation. A stock of Golden Spur that had deteri- orated because of heavy removal of salable bulbs was treated 2 years ill succession. The resulting growth was very much improved in vigor and the bulb increase was decidedly high. Gray or streaked fohage (due to poor growth, not virus disease) which had been prevalent almost entirely disappeared after the treatments. A special stimulating effect was noted in a stock of the variety Lucifer. For several years this stock had been apparently deteriorat- ing or "running down," as evidenced by the foliage showing light- colored streaking similar to virus infection. After the vapor-heat treatment vi^as applied the foliage had a very vigorous appearance quite green, and unmarked by streakings. The harvested bulbs were considered of better grade and quaUty than in any previous year 1 he grower considered that this was due to the softening of the heavy corky base typical of this variety, which normally would retard root development. Root development has been observed to start considerably earlier when the bulbs have been treated, and this is perhaps the most important factor responsible for the general stimulation associated with vapor-heat treatment. VAPOR-HKAT TllKAÏMENT ]'X)n XARCIäSUS BULB PESTS 51

PRACTICAL APPUCATION OF VAPOR-HEAT TREATMENT FOR PLANTING STOCKS The grower who wishes to use vapor-heat treatment for planting stocks would have in mind the resulting control of the several bulb pests, namely, the bulb flies, the bulb mites, and nematodes. The control of all these by a single treatment is of course the most practical. Nematode control requires the longest period of treatment, hence a duration suiRcient for satisfactory results against that pest would be more than sufficient for complete mortality of the others. Whether intended as a precautionary measure or for the control of an actual infestation, a treatment for nematodes must be of not less than 8 hours' duration at 110° to 111° F. and must be applied in the early part of the storage season. The most practical time for treatment would be immediately after removal of the salable bulbs. in case the grower's primary interest is directed toward the control of bulb flies and mites only, a 2-hour treatment at 110° to 111° F. is sufficient. The results in controlling these pests are not affected by the season of treatment, except that any treatment should be made before the bulbs show signs of roots sprouting or tip growth, because the bulbs are very susceptible to injury when in such condition.

ADVANTAGES OF VAPOR-HEAT TREATMENT The two treatments commonly used for the control of bulb pests have certain disadvantages that are eliminated in vapor-heat treatment. Cyanide fumigation is utilized only for the control of the larvae of the bulb flies. It is used principally for those bulbs that are moved in conmiercial channels and is not particularly adaptable to the treatment of planting stocks because it is ineffective against either of the bulb mites or the bulb nematode. Hot-water treatment has been used principally as a control of the bulb nematode. This method is somewhat slow in operation because of limited capacity of the dipping tanks and involves considerable labor. Further, the bulbs after treatment are wet and must be carefully tlried unless they are immediately planted. Unless fungi- cides are used with the hot-water method, the water serves as an avenue of spread of various disease organisms from bulb to bulb. Vapor-heat treatment ofl'ers the advantages of effectiveness against all the principal bulb pests; speed of operation; convenience of manip- ulation from two standpoints, (1) ease in loading and unloading, and (2) elimination of the necessity of further drying of the bulbs following treatment; and reasonably low cost of operation. The speed with which a stock of bulbs may be treated is due to the large pt)tential capacity of the equipment, which can be designed to handle as high as 20 tons or more of stock per load. With this equipment the regular storage trays are used, eliminating the need of special containers. The trays in stacks can be trucked into and out of the treathig room, which reduces labor. A satisfactory practice has been to treat a load every other day; or, if every day to unload and reload the first thhig in the morning, after which only one man is needed to operate the equipment. After treatment the bulbs are dry and so can be immediately returned to storage. 52 TECHNICAL BULLETIN 672 IT. S. DEPT. OF AGUICULTUlíE

SUMMARY Immersion in liot water has been generally practiced for the elimination of the narcissus fly {Merodon equedri^); tlie lesser bulb flies {Eumerus tuberculatus, E. strigatus, and E. narcissi); tlie bulb scale mite (Tarsonemus approximatus var. narcissi); the bulb mite (Rhizo- glyphus hyacinthi); and the bulb nematode {Ditylenchus dipsaci). In view of the development of the vapor-heat method for Mediter- ranean fruitfly control in Florida, studies were conducted at Sumner, Wash., to determine the adaptability of this method for thermal treatment of narcissus bulbs in the Pacific Northwest, as an alternative to the hot-water method. In the experimental work it was determined that a treatment temperature of 110° to 111° F. was the most favorable. This temperature has been used as a standard in the hot-water treatment also. The minimum durations at this temperature necessary for complete mortality of the insects and mites were determined as follows: (1) Nar- cissus fly, Iji hours; (2) lesser bulb flies, l'A hours; (3) bulb scale mite, one-half hour; (4) bulb mite, one-half hour. In the experimental results thus far obtained, almost complete control of the bulb nematode has been produced by 8-hour treatments at 110° to 111° F. during the earher part of the storage season. When bulbs are intended for greeidiouse-flower production, satisfactory results may be obtained by treating the bulbs for not more than 2 hours at 110° to 111° F. for insect and mite control, during the first half of August, after at least 3 weeks of drying. Attention must be given to varietal difl'erences in tolerance. Poétaz, poeticus, polyanthus, and tnzetta types respond favorably only to early-season treatments. Bulbs intended for field planting for bulb production tolerate treatments of long duration and the effect on flowers is not associated with the effect on bulb increase. Although the period during which treatments may be given with satisfactory results was found to be extensive, the preliminary results obtained in the nematode-control studies indicate that treatment should be given soon after the bulbs are dug. For planting stocks the 8-hour duration at 110° to 111 ° F. necessary for nematode control is desirable as a protective measure. Bulbs may be treated in consecutive seasons without fear of detrimental effects. Ceresan treatment for control of basal rot is compatahle with vapor- heat treatment. When properly applied, vapor-heat treatnuMit of planting stocks niay he expected to result m vigorous giowlli and an above-normal increase m l>ull) ¡¡roduction.

LITERATURE CITED (1) C'KEAOEH, D. R., and SPRDLJT, F. .J. 19.3.'-). THE REL.VrlON OP CERTAIN FUNGI TO LARVAL DEVELOPMENT OP EDMERUS TUBERCDLATU.S ROND. (KYRPHIDAE, DIPTERA). Ann. ,„, „ ^i'lit. Soc. Amer. 28: 425-437, ilhis. (2) HAWKINS, LON A. ]!);í2. STERILIZATION OF CITRUS FRUIT BY HEAT. Tex. L'itric. 9 (1): VAPOR-HEAT TREATMENT FOR KARCISSUS BULB I'ESTS 53

(3) LATTA, RANDALL. 1932. THE VAPOR-HEAT TREATMENT AS APPLIED TO THE CONTROL OF NARCISSUS PESTS. Jour. PJcoii. Eilt. 25: 1020-1026, illus. (4) 1932. THE VAPOR-HEAT TREATMENT FOR NARCISSUS BULBS. Wash. State Hort. Assoc. Proc. Ann. Meeting 28: 294-297. (5) SPRUIJT, F. .!., and BLANTON, F. S. 1933. VAPOR-HEAT TREATMENT FOR THE CONTROL OF BULB PESTS AND ITS EFFECT UPON THE GROWTH OF NARCISSUS BULBS. JoUr. Econ. Ent. 26: 613-620. (6) RAMSBOTTOM, J. K. 1918. EXPERIMENTS ON THE CONTROL OF EELWOEM DISEASE OF NARCISSUS. .Jour. Roy. Hort. Soc. 43: 65-78. (7) SLOGTEREN, E. VAN. 1919. DE TOEPASSING VAN WAHMTE ALS BESTIUJDINGSMIDDEL VAN EENIGE BLOEMBOLLENZIEKTEN. Weekblad voor BloeniboUenciilt. 30: 63-66, [691-71. (8) 1920. DE NEMATODEN-BESTRMDING IN DE BLOEMBOLLENSTREEK. Tijdschr. Plaiitenzicktcn 26: [118J-138, 161-171, 177-188, illus. ORGANIZATION OF THE UNITED STATES DEPARTMENT OF AGRICULTURE WHEN THIS PUBLICATION WAS LAST PRINTED

Secretary af Agriculture HENKY A. WALLACE. Undersecretary M. L. WILSON. Assifstant Secretary HAHRY I>. BKOWN. Coordinator of Land Use Planning and Di- M. S. EISENHOWER. rector of Information. Director of Extension Work C. W. WARBURTON. Director of Finance W. A. JUMP. Director of Personnel ROY F. HENDRICKSON. Director of Research JAMES T. JARDINE. Solicitor MASTíN G. WHITE. Agricultural Adjustment Administration^. _ H. R. T01A.YIY, Administrator. Bureau of Agricultural Economics A.G.BLACK, Chief. Bureau of Agricultural Engineering S. H. MCCRORY, Chief. Bureau of Animal Industry JOHN R. MOHLER, Chief. Bureau of Biological Survey IRA N . GABRIELSON, Chief. Bureau of Chemistry and Soils HENRY O. KNIGHT, Chief. Commodity Exchange Adtninistration J. W. T. DTJVEL, Chief. Bureau of Dairy Industry O. E. REED, Chief. Bureau of Entomology and Plant Quarantine^ LEE A. STRONG, Chief. Office of Experiment Stations JAMES T. JARDINE, Chief. Farm Security Administration W. W. ALEXANDER, Administrator. Food and Drug Administration WALTER G. CAMPBELL, Chief. Forest Service FERDINAND A. SILCOX, Chief. Bureau of Home Economics LOUISE STANLEY, Chief. Library CLARIBEL R. BARNETT, Librarian. Bureau of Plant Industry E. C. AUCHTER, Chief. Bureau of Public Roads THOMAS H. MACDONALD, Chief. Soil Conservation Service H. H. BENNETT, Chief. Weather Bureau F. W. REICHBLDERPER, Chief.

Thi.s liuUctin is a cciitriljutioii from

Bureau of Entomology and Plard Quarantine LEE A, STRONíí, Chief. Division of Track Crop and Garden W. H. WHITE^ Principal Ento- Insect Investigations. mologist, in Charge. 54

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