LitSKAK I STATE PLANT BOARD May 1946 United States D apartment of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine CONTROL OF ORCHID-INFESTING INSECTS BY VAULT FUMIGATION WITH METHIL BROMIDE During 1941 and 1942 extensive experimentation was performed at and near Hoboken, N. J., on the fumigation of growing orchid plants with methyl bromide. These studies were planned to provide data upon which treatments could be recommended for the fumigation of orchid plants imported into this country under the provisions of the Nursery Stock, Plant, and Seed Quarantine No. 37* 'administered by the Bureau of Entomology and Plant Quarantine. Since it was impractical to obtain plants of foreign origin for these studies, domestic orchid plants were used. Cooperation was arranged with several orchid growers at Summit, West Orange, Bergen- field, and Woodcliff, N. J., whereby plants could b® borrowed for these studies. A number of cases of methyl bromide injury to orchid plants had been reported, particularly on Cymbidium and Cypripedium, where such * plants were included with plant material treated for other than orchid insects. The dosage schedules in the present studies were from 1.25 to 2 pounds of methyl bromide per 1,000 cubic feet of vault space for from 1.5 to 2 hours. These amounts, which were relatively light in comparison with dosages of methyl bromide used for other purposes, were effective against insects on orchid plants, and the orchids in general reacted favorably to these schedules. The results of these studies not only provided a basis for recommendations relative to the treatment of imported orchid plants, but suggested a possible means of practical control for scale in- sects, mealybugs, or other insects which cause a considerable loss to domestic orchid growers each year. Studies on insect mortality and plant tolerance were carried on simultaneously, usually on the same plants* By Jacob W. Bulger Division of Control Investigations Experimental Procedure ftUN 1 5 1946 - 2 Each fumigation was assigned a number, and all plants in the test were labeled with this number. A record was prepared, giving data on the date, temperature, dosage and exposure, varieties of plants and numbers of each included, and any other pertinent infor- mation. Later records on insect mortality or plant reaction were identified with the fumigation test number. All fumigations were performed in gastight vaults. The potted plants were removed from the benches and placed in the vault. Methyl bromide was carefully measured in a special applicator, and introduced into the closed vault, where it immediately volatilized. A small fan within the vault kept the air-gas mixture agitated for the first 15 minutes of fumigation. At the end of the exposure period the gas was removed from the vault by a venting system, and the plants were removed to a shaded place for a period of aeration before being returned to the greenhouse. In each test, after being returned to the greenhouse benches, the plants were kept isolated until final observations on mortality were made 10 to 20 days following treatment. This post fumigation holding period allowed affected scales to change appearance, and any remaining viable eggs to hatch. Counts on mealybugs were made IS to 72 hours after treatment, since they tended to fall off the host plants if left longer. Mealybug eggs were observed for 10 days or longer. Most of the studies on insect mortality were directed toward the various species of scale insects found in New Jersey orchid establishments. As soon as the approximate lethal dosage to these species was determined, studies on plant tolerance were expanded. At the beginning of the investigation limited numbers of plants were used, and careful records kept on each plant* As the studies progressed, larger numbers of plants were used, and it became imprac- tical to keep such detailed records; therefore, notes were restricted to more general observations. Complete records were kept of the varieties treated, however. Fumigation tests in the fall of 1941 were performed at the Plant Inspection House at Hoboken, The plants were replaced in their owner's establishments within a day or so following treatment, so that they could be kept for observation under their usual greenhouse environment • Opportunity was afforded for studying the reaction of one lot of fumigated plants before proceeding with the fumigation of others* By this cautious approach the tolerance of many orchids was obtained. By February 1942 continued favorable plant reaction to dosages lethal to most of the scale insect e involved prompted one grower to offer a complete house of assorted orchids for experimental treat- ment in return for the benefit to be derived from a cleanup of this greenhouse. Accordingly, a vault of 33 cubic feet was installed in the head house of his range, and the contents of one house (fig. 1) were methodically treated, from 30 to 200 plants at a time. This grower handled all the plants, and shortly after the start of this program also took over, under supervision, the application of the fumigant. All subsequent reference to'*the grower 1 ' in this paper re- fers to this operator. The cooperative arrangement covered approximately 18 months, which allowed observations to be made on fumigations performed in both winter and summer, under various atmospheric and other condi- tions, and at temperatures ranging from 50° to 95° F. Studies on Insect Mortality Ten species of scale insects and one species of mealybug were found in orchid houses in the New Jersey area, and the effect of methyl bromide fumigation was studied on all of them. Scientific name Common name Found on- Chrysomphalus aonidum (L.) Coccus hesperidum L. Coccus pseudohesperidum -TckTiTT — Diaspis boisduvalii Sign. Lepidosaphes ?mackieana McKenzie Lepidosaphes machili (Mask.) Parlatoria proteus Curt. Pseudoparlatoria parla- torioides (Comst,) Pulvinaria floccif era (Westw. ) Saissetia hemispherica (Targ.) Pseudococcus sp. (close to maritimus) Florida red scale Qncidium sphacela- tum chiefly MaxiUaria, Bendro- bium and miscel- laneous orchids Most genera Soft scale Soft scale White scale All varieties Oyster shell scale Dendrobium Cymbidium Black scale of orchids Hemispherical scale Mealybug Cypripedium (Summit) Cypripedium (Bergenfield) Oncidium and mis- cellaneous orchids Ardesia To some extent on most varieties Further results of the studies are given in table 1. A dosage of 1*75 pounds of methyl bromide per 1,000 cubic feet of vault space for 2 hours consistently gave complete mortality of all armored scales and mealybugs. Complete mortality of soft scales was not ob- tained, but it was high enough to give practical control. Specimens of Lepidosaphes sp. from Dendrobium, sent to special- ists in the Division of Insect Identification, were returned as Lepidosaphes flnackieana UcKenzie*V In the meantime the infestation was apparently wiped out, as subsequent observations failed to reveal any live specimens* All stages of the mealybug proved to be killed readily with the dosages tested. Only one species appeared to be present in the orchid greenhouses observed in the New Jersey area, identified as Pseudococcus sp. (close to maritimus ) . One specimen of Cerataphis lataniae , an aphid, with a scale-like appearance, was killed by a dosage of 1.75 pounds for 2 hours. After a lot of plants had been fumigated, infestation was a long time in reappearing, and then it was restricted to isolated groups which were easily cleaned up by r ©fumigation of a small num- ber of plants. Studies on Plant Reaction A total of 16,172 plants, representing 56 genera, were included in the studies on plant reaction. Figure 1 shows a greenhouse filled with Cattleya, Stanhopea, Oncidium, Dendrobium, and miscellaneous types which were fumigated during July and August 1942, as they appeared 4 months later. The general condition was considered as excellent. It was observed that the older leaves or the injured leaves (fig. 6) of fumigated plants often became discolored and dropped off in a few days or weeks. While this condition was definitely asso- ciated with fumigation, no characteristic burn or injury was avi In fact each stage of discoloration could be matched with similar^ colored leaves from untreated plants, except that in the latter in- stance the process of discoloration and loss was spread over joonths instead of days. It was suggested that perhaps methyl bromide, caused a premature and rapid ripening of the older leaves. At first this occurrence was regarded as serious, but upon long and careful observation the grower concluded it to be of minor consequence, since fumigated plants tended to produce excellent new growth and, in some cases, appeared to be stimulated by the fumigation. 1/ McKenzie, H. L. Miscellaneous diaspid studies, including notes on Chrysomphalus (Homopteraj Coccoideaj Diaspididae). Calif. Dept. Agr. Bui. 32: H8-162, illus. 1943. The post fumigation handling of the plants influenced the plant reaction under certain circumstances. In two consecutive tests on a sunny day during the midsummer of 1942, plants of Cattleya Bowringiana were fumigated at 75° F. in the morning and at 88° in the afternoon, and immediately replaced in the greenhouse, where shading was normal for summer. The plants fumigated in the morning and replaced at about 11 a.m. showed injury to fairly sound leaves, whereas those fumigated in the afternoon and replaced about 5 p.m. . showed no injury. The injury was similar to that which orchid grow- ers attribute to too much sunlight. A review of all previous tests showed that the occasional in- stances of injury were usually in tests made in the morning, and that afternoon tests seldom showed any injury. This difference was attributed to the additional sunlight, or bright light, to which the plants from morning fumigations were exposed. Subsequently all plants were kept in deep shade (usually in the head house) for sev- eral hours following fumigation, and further injury of this type was prevented. The detailed results are given in table 2. Under the heading of injury, the loss of old leaves is not considered. All names are listed as shown in the growers 1 catalog and have not been checked botanically. For greater convenience, the response of plants is discussed by groups. Response of Various Groups of Orchids to Methyl Bromide Fumigation Cattleya . — -In general, plants of the Cattleya group responded well to methyl bromide fumigation. Vigorous plants responded better than weak ones. Growth buds and eyes were not injured, even at dos- ages in excess of those discussed in this article. Plants with heavy infestations of scale insects encrusted on the leaves shower spotting under such scale patches, but this was judged to be due insect injury. The loss of older or injured leaves was more pro- nounced on the Cattleya than upon other orchids. Plants with yellowed leaves showed greater loss than those with deep green leaves. Plants in full bloom were fumigated without injury to either plant or flowers. In one case a blossom just opened and not yet hardened was uninjured. A peculiar spotting appeared occasionally on the Cattleya hybrids Enid, Fabia, and Gigas, on the bud-sheath leaf at a point just below the top of the sheath. As the leaf elongated with the development of the bud, the spot appeared past the end of the sheath. No injury to the bud or flower was evident. The cause of the spotting was not determined. - 6 - Seedling Cattleya responded well and showed no adverse reaction to fumigation. The condition of plants improved after being fumigated. The prevention of insect injury apparently offset any fumigation injury to the plants. The grower repeatedly commented on this favorable reaction of fumigated plants. Cymbidium . — The orchids of the Cymbidium group, particularly the older plants, had a tendency to lose a considerable amount of foliage following fumigation. As with the Cattleya, the older, out- side leaves were lost. New growths, buds, and flowers were not in- jured (fig. 3)» Seedlings responded very well after fumigation, and lost few leaves. At first the loss of leaves was considered objectionable, but after seeing the later response (figs. 3 and 4) of fumigated plants the greenhouse operator fumigated all of his Cymbidium. Extreme care should be taken with plants of this group, how- ever, and preliminary tests should be made before fumigating any number of them. In early tests a few Cymbidium plants were fumi- gated with dosages above those discussed here, and severe defolia- tion followed. Some of these plants were killed, and the remainder were retarded for 2 years or more before regaining a semblance of normality. Dosages of more than 2 pounds per 1,000 cubic feet should not be used. Cypripedium .— With but few exceptions, orchid plants of this group were successfully fumigated with dosages up to 2 pounds per 1,000 cubic feet for 2 hours (fig. 5). Plants of C. Aureum Oedippe and C. Aureum Virginal e lost some foliage but within 2 months they were better than before fumigation. Plants of several varieties were not injured when in bud or in full bloom. . One plant of Selenipedium Urgandae Graves var. was seriously injured, but new growth survived. The plant recovered later but was retarded materially. Other varieties of Selenipedium showed no injury. Dendrobium. — In the initial tests upon this group of orchids the grower was concerned by the heavy loss of foliage. In some varieties all leaves dropped except the greenest ones at the tip of the canes. (Plants normally lose this foliage by the end of the season.) Within 2 months after fumigation the plants had produced such excellent new growth that the grower decided to fumigate his entire stock of Dendrobium. Plants in full bloom were fumigated without injury to the flowers. Oncidium .— Most species in this group responded well to dosages up to 2 pounds per 1,000 cubic feet for 2 hours. As with other genera, old and defective foliage was sometimes dropped, but no sub- stantial injury resulted. Generally the leaf loss was greater in the thin-leafed than in the thick-leafed varieties. One exception to this was with plants of 0. Ampliatum var. Majus* In one or two tests on this orchid with the maximum dosage there was a consider- able leaf injury. 0. Sphacelatum and Powelii (thin-leafed) in some tests also showed leaf loss. There is a question, however, as to whether this loss was not due to exposure to bright light following fumigation. In some cases these plants responded very well. Re- covery was rapid aiod injury was not considered serious. Caution should be exercised in the treatment of 0. Ampliatum Ma jus until more is known of its reaction to fumigation. Laelia . — No injury whatsoever was observed in varieties of this genus, with dosages up to the limit tried. The grower reported his plants in excellent condition, and that the yield of flowers had been exceptionally high. Phalaenopsls .-"Orchids in this genus also reacted favorably fol- lowing fumigation with the maximum dosages used. Some varieties showed no injury when fumigated with dosages considerably above this in other tests. Miscellaneous, orchids. — Miltonia orchids responded well in all test 8 (fig. 2), as did varieties of Odontoglossum, Angraecum, Calanthe, Phaius, and lycaste. The foliage of the last' three is similar* Plants of Calanthe, which appeared to have the most tender leaves, showed no injury in the experiments. Plants of Phaius, ap- parently harder leafed, showed some spotting, particularly where a leaf had been mechanically injured before fumigation. Plants of lycaste appeared to respond slightly better than Phaius, but occasion- ally showed some spotting. Epidendrum are rather tolerant and responded like Cattleya. The reaction of numerous other genera listed in table.) 2 was ger erally favorable, with one exception, Zygopetalum Mackayii, which was rather severely injured. More information is needed ob\ the tol- erance of this variety until the reason for injury is known. In some instances injury occurred which would prevent the immediate sale of the injured plants, but which did not causa last- ing detriment or interfere with division for propagation. Practical Application of This Method The foregoing experiments indicate that methyl bromide fumiga- tion has a distinct possibility of being adaptable for the use.) of . domestic orchid growers. - e - The data show that by this method mealybugs and armored scale insects can be completely cleaned up, and soft scales effectively controlled at dosages safe to most varieties of orchids. The data indicate> however, that the margin between insect con- trol and plant injury is harrow, so that practical fumigation must be performed precisely if injury is to be avoided. Some los3 of foliage may occur even if fumigation is precisely performed, but generally the degree of insect control and the response, of the plants offset the initial loss of older leaves. For practical use, a dosage of 1,75 pounds of methyl bromide per 1,000 cubic feet of vault space for 2 hours at 70° F. or above is recommended. This dosage apparently will cause complete mortal- • ity of armored scales and mealybugs, and effect as good control of soft scales as the next higher dosage tested. For growers who wish to maintain a greater margin of plant safety, a dosage of 1.5 pounds per 1,000 cubic- feet for the same period will apparently lower the efficiency of the treatment only slightly. Orchid growers utilizing this method are cautioned on the fol- lowing points: (1) Fumigate only small numbers of plants at first, until ex- perience is gained, and never fumigate more than modest numbers of plants. By dividing treatments into small lots the chance of an error that might cause consider- able financial loss is reduced. (2) Allow only a skilled operator to perform the fumigations* This task must be performed precisely at recommended dos- ages. An unskilled or irresponsible person may cause severe injury to plants by overexposure or overdosage. (3) Aerate plants well after the fumigation and keep them out of sunlight or strong light for at least 24 hours. Dur- ing this period there should be good air circulation around the plants. (4) When returning plants to the range, place them on clean benches and isolate them as much as possible from unfum- igated plants and other vegetation that may harbor in- sects. (5) The humidity in the vault during fumigation should be high and pots should not be dry. (6) Fumigation in the summer when temperatures are high and the sun bright may be hazardous. - 9 - The feasibility of this method of insect control in commercial orchid houses has been adequately demonstrated by the grower who cooperated in making these tests. A letter from him, dated January 1944, sums up his experience as follows: "We have been continuing our fumigation, although not in the proportions that I would like, right along and *** our work is more successful than ever now. It has been proving itself of immense value in many ways. A little instance of this is our Oncidiums, which were quite heavily infested with Mealy Bug and your long, woolly white friend with the yellow head. Pulvinaria floe cif era . This year we had a magnificent lot of spikes from our mixed Oncidiums, which include varicosum,f orbesi, crispiun, etc., and we have been cutting some beautiful spikes of splendidum. Of the latter, we are way ahead of anything we have ever had in both size of spike and quality of flower. "We have just finished fumigating our Oncidiums again, although *** 60 to 70 percent of them were very clean and free from any of the pests they previously had. We lose very few leaves now, as immediately upon completion of the fumigation we place them in a very shaded position and syringe thera at least twice a day for 4 or 5 days. We syringe all the plants that we are now fumigating before putting them in the fumigator. i do not think we lost 100 leaves out of the en- tire last fumigation of Oncidiums in which we must have had some 600 or 700 plants. have also increased the dosage and time, and do not give anything less than 2 pounds for 2 hours. "Another very nice proven result is our Laelias, ' which as you know, were in some cases completely covered with that hard, small scale that is so hard to kill by spraying ( Coccus ) . At this writing I doubt if you can find a more healthy, clean looking lot of Laelias anywhere. With very few exceptions, I have not been able to find a single scale or insect. *" JH{ They are absolutely clean of everything and are rewarding us beautifully in flowers. "Our Cypripediuras are very fine and as clean right now as the Laelias - 10 - •HHt* i *** would like to cite one more example in our Cymbidiums. As you know, I was never too enthusiastic about them and they grew and flowered quite well, and alto collected a great deal of various scale, including the same small one that the Laelias seem to be fond of. Right now, we wouldn't take a back seat to anyone in condition of plants and magnificent flower spikes. The foliage just ac- tually shines and is of a good deep color with enormous leading bulbs and tremendous spikes. I have counted up to 32 buds in some instances on a single spike. "Of course, I feel very enthusiastic about this treatment and I know a good percentage of the improvement is due to fumigation*"**." Further information concerning the use of methyl bromide or the construction of a fumigation vault can be obtained by writing to the Bureau of Entomology and Plant Quarantine, U. S. Department of Agri- culture, Washington 25, D. C. « - 9 - The feasibility of this method of insect control in commercial orchid houses has been adequately demonstrated by the grower who cooperated in making these tests* A letter from him, dated January ,1944, sums up his experience as follows: "We have been continuing our fumigation, although not in the proportions that I would like, right along and *** our work is more successful than ever now. It has been proving itself of immense value in many ways. A little instance of this is our Oncidiums, which were quite heavily infested with Mealy Bug and your long, woolly white friend with the yellow head. Pulvinaria floccif era . This year we had a magnificent lot of spikes from our mixed Oncidiums, which include varicosura,f orbesi, crispum, etc., and we have been cutting some beautiful spikes of splendidum. Of the latter, we are way ahead of anything we have ever had in both size of spike and quality of flower. "We have just finished fumigating our Oncidiums again, although *** 60 to 70 percent of them were very clean and free from any of the pests they previously had. We lose very few leaves now, as immediately upon completion of the fumigation we place them in a very shaded position and syringe them at least twice a day for 4 or 5 days. *** We syringe all the plants that we are now fumigating before putting them in the fumigator. i do not think we lost 100 leaves out of the en- tire last fumigation of Oncidiums in which we must have had some 600 or 700 plants. have also increased the dosage and time, and do not give anything less than 2 pounds for 2 hours. "Another very nice proven result is our Laelias, which as you know, were in some cases completely covered with that hard, small scale that is so hard to kill by spraying ( Coccus ) ♦ At this writing I doubt if you can find a more healthy, clean looking lot of Laelias anywhere. With very few exceptions, I have not been able to find a single scale or insect. ***They are absolutely clean of everything and are rewarding us beautifully in flowers. "Our Cypripediums are very fine and as clean right now as the Laelias - 10 - ■«#■&* I *** would like to cite one more example in our Cymbidiums. As you know, I was never too enthusiastic about them and they grew and flowered quite well, and alto collected a great deal of various scale, including the same small one that the Laelias seem to be fond of. Right now, we wouldn't take a back seat to anyone in condition of plants and magnificent flower spikes. The foliage just ac- tually shines and is of a good deep color with enormous leading bulbs and tremendous spikes. I have counted up to 32 buds in some instances on a single spike. "Of course, I feel very enthusiastic about this treatment and I know a good percentage of the improvement is due to fumigation***." Further information concerning the use of methyl bromide or the construction of a fumigation vault can be obtained by writing to the Bureau of Entomology and Plant Quarantine, U. S. Department of Agri- culture, Washington 25, D. C. -II - © n o & «d 9 CO to o •d ti © 05 O •H •d +» AS >» *» •H ♦» o •d o CM « CM j3 O iH O £1 n •d o P. 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H CVJ S- VP sill ~ 4* 9 * p Pi a p w a c 4 u o 25 U j u J fa i ■2 i CVj CM iH CM WVO K> CM I O i-< rH CM I 1 1 1 1 I | J I I I 1 I i I i 1 1 1 [ 1 1 1 1 1 i I i 1 rH 1 1 1 1 1 i i i CM CM CM 1 1 m 1 1 r4 1 1 1 1 1 H m 1 1 1 1 1 i i 1 t t 1 1 t l 1 1 1 1 1 1 1 1 1 1 i 1 1 1 1 1 I i i 1 1 1 1 1 I i 1 1 1 1 1 i i 1 1 1 1 i i VD VX> r— VOVO CM vr> CM CM in o cm cm 5b cm m cm So CM iH vo r— I I d 81 d •*» «H U i-t -H « 3 • o fl O «H 3 •hS • d a tffttflS • . • «4 g • J ^ MdS««H«H«H«H 43 o fi +» o d ft 3 ft d OtT!J 8 5, ♦JOH MM H« ^ WHP Of3 <0 - 28 to UN to c •H 1 O I I • CM 0) rH a 1 o 8 Figure 1. — General view of a greenhouse in which all plants have been fumigated. Plants in the low bed at the left are seedling white Cattleya. . Those hanging overhead on the right are Cattleya Gigas. Plants on the inclined bench to the right are mostly Cattleya Enid hybrids. Those in willow baskets are Stanhopea. Elsewhere are many other species of orchids. Figure 2. — lliltonia orchid plants in excellent condition following fumigation. Figure 3» — Cymbidium plant fumigated twice, in October and in February, Plant was in full bloom when fumigated the second time. LIBRARY STATE PLANT BOARD Figure 4* — Other Cymbidium 7 months after fumigation. Figure 5» — Cypripedium Insigne fumigated without injury. - Figure 6. — Typical discoloration centering around a previous mechanical injury. V > t v UNIVERSITY OF FLORIDA \