This brief paper is dogmatic in treatment, simply because my audience knows already the declarations to be true, and I offer it merely as a reminder and generalization of already acquired knowledge. FUMIGATING GREENHOUSES WITH HYDROCYANIC ACID GAS. BY R. WELLINGTON, Experiment Station, Geneva, N. Y. The fumigation of greenhouses with hydrocyanic acid gas for the destruction of insects is by no means a new subject, for at the present time it is extensively employed in Europe and North America. Yet, previous to 1895, when Woods and Dorsett (1) of the United States Department of Agriculture, commenced their experiments, no recommendations for its use were in existence. These men, after a series of carefully conducted experiments, arrived at the conclusion, that as a rule, plants were less injured by short exposure to a relatively large amount of gas than by long exposure to a relatively small amount. In an exposure of twenty minutes with 0.075 grams of potassium cyanide (ninety-eight per cent purity) per cubic foot of space the following ferns, Davallia mooreana, Adiantum cuneatum and Adiantum Ballii, were unharmed. One-tenth of a gram of KCN with the same length exposure caused no injury to several varieties of coleus. Single violets, as California. and Princess of Wales, however, were injured with a short exposure to 0.15 gram KCN per cubic foot, while the double English varieties were unaffected by the same treatment. The young growth of roses was also found to be particularly sensitive to the hydrocyanic acid gas. In these experiments ninety per cent of the plant lice were killed, but the thrips were unharmed. Two successful "all night" fumigations with hydrocyanic acid. gas are cited. In one case 0.09 gram per cubic foot produced no injury to grape vines grown under glass in New Zealand, and in the other a dose of 0.028 gram killed the white fly (Aleyrodes vaporariorun Westw.) and caused no injury to a house of tomato plants. This method of treatment was mentioned as interesting, but not as an established practice. A. W. Morrill (2, 3), who has made extensive studies of the white fly, credited this insect with feeding on about sixty different kinds of plants-probably the number of known kinds is now much greater. As this insect causes the death or impairs the vitality of many of the main greenhouse crops in this and other countries, and as potassium cyanide is the only known successful combatant, the value of this chemical as a fumigant is very high. By the employment of three treatments at intervals of twelve days to two weeks apart, Morrill found that he could practically control this pest, even in very badly infested houses. Although 0.005 gram of potassium cyanide to a cubic foot was found sufficiently strong to kill many of the larvae and all the adult white flies-not the eggs and late pupal stage-0.007 gram per cubic foot with an exposure not exceeding three hours, was recommended as the best known strength for the fumigation of either cucumbers or tomatoes. However, for an initial treatment, the 0.005 gram per cubic foot was recommended, with the provision that if this amount did not kill the insects, to increase the same by 0.001 gram on each subsequent trial (which should be at least three days apart so that the results can be noted), until a strength was obtained which would destroy the larvae and not injure the tender leaves of the plants. C. O. Houghton (4), of the Delaware Experiment Station, severely injured a house of lettuce by fumigating during the day time with 0.1 gram KCN per cubic foot of space for a period of fifteen minutes. The same treatment, on another occasion, produced no injury when the foliage was dry. In his later experiments, he fumigated the greenhouses with 0.005 gram KCN per cubic foot for periods of twenty-five minutes, thirty-five minutes, and all night duration. These treatments killed all the aphides and most of the aleyrodes. Rose bushes, tomatoes, lettuce, carnations, hydrangas and calla lilies suffered no injury in these later trials. From Houghton's work, we can conclude that it is dangerous to fumigate during the day time and when the foliage is wet. W. V. Tower (5), after performing several experiments on the amount of potassium cyanide requisite for controlling the white fly, arrived at the same conclusion as Houghton, that less injury to the plants was produced when the fumigation was performed at night-the safest treatments being on cloudy nights following dark days. Tower noted little effect of temperature on the amount of injury to plants. The common opinion, however, is that less injury is produced when the house is on the "cool side." As a general rule, Tower found that prolonged exposures to weak strengths of gas were more injurious to the plants than shorter exposures with greater strengths. Dr. H. T. Fernald, who formulated these conclusions from Tower's work, recommended the use of 0.015 gram of KCN per cubic foot for a period of from forty-five to sixty minutes, even though he thought this strength might slightly injure tomato foliage under certain conditions. C. W. Hooker (5) in his cucumber fumigation experiments found that a clear, dry evening without moonlight, with a temperature in the house of from fifty-five to sixty-five degrees, or a cloudy evening with the same temperature, offers the best conditions for fumigation. Hooker's experiment indicated that a small amount of potassium cyanide with a longer exposure is preferable to a large amount for a shorter exposure. The difference in behavior of the tomatoes and cucumbers to the effect of the hydrocyanic acid gas was explained by the greater hardiness of the latter. Constantin, Gérome, and Labroy (6) of France, have secured interesting and favorable results in their potassium cyanide fumigation work. But unlike their American co-workers, they used much stronger doses of gas from 2% to 3% grams of KCN per cubic mètre of space, or in other words, about 0.07 to 0.1 gram per cubic foot. The length of the exposures varied from thirty to sixty minutes, the time and amount of KCN used depending on the hardiness of the treated plants. In their work they killed the hardy red spider, thrips, mealy bug and other pests and injured only a few of the many treated ornamental plants. For a day or two after fumigating, they noted that their plants transpired with difficulty and consequently diminished the amount of watering until the plants had regained their normal condition. It is rather difficult to understand why such strong dosages did not severely injure all the treated plants. This fact, however, is interesting, as it illustrates how dangerous it is to put too much confidence in a few experiments, especially, when they apply only to certain conditions. The usage of sodium cyanide, as a greenhouse fumigant, instead of potassium cyanide, has been reported with success by English growers, but little work seems to have been done in America with this chemical (7). A brief review of several investigators' results with hydrocyanic acid gas fumigation has been given with the purpose of pointing out the variability of results that have been obtained in different places and under varying conditions. The writer has no new discoveries to add to the ones already presented but he wishes to state his experiences in order to confirm and substantiate the statements made by other investigators. During the spring of 1907, the greenhouses at the New York Agricultural Experiment Station were so badly infested with the aleyrodes that it was impossible to carry on experiments with any degree of success. Tobacco fumigants had been tried repeatedly. but had given poor or not any results. On April 12, a house of cucumbers with plants averaging about eight inches in height, was fumigated with 0.01 gram of potassium cyanide per cubic foot of space with an exposure lasting through the night. The gas killed all the white fly and slightly injured the edges of a few leaves, the injury appearing two or three days after the date of fumigation. A few potted lettuce plants and a few young cabbage plants in the same house had their leaves severely injured. On May 11 another house containing mostly musk-melons and a few pepper, tomato and egg plants, was fumigated all night with a weaker strength, viz., 0.0075 gram to the cubic foot. This dosage apparently killed all the aleyrodes and caused no injury to the plants. On May 29 a third house devoted mainly to ornamental plants was fumigated with the same strength of potassium cyanide as the second one, and for the same length of time. The treated ferns, palms, begonias, asters, geraniums, nasturtiums, cauliflowers and several other plants showed no injury. A few leaves of alfalfa seedlings and chrysanthemums, however, developed a slight injury. Since 1907, these three houses producing crops of lettuce, cucumbers, melons, tomatoes and ornamentals, have been fumigated sev eral times each year with the same strength, 0.0075 grams* KCN per cubic foot, and with very creditable results. Only once have the tomato plants shown a marked injury to the terminal leaves and the extremities of the stems and, at this time, the injury occurred when the vines were fumigated by a new man. The same amount of potassium cyanide to the cubic foot was used by the writer in fumigating a greenhouse at Bussey Institution, Jamaica Plain, Massachusetts, and results similar to those in New York, were obtained. The foliage of Nicotiana glutinosa, Salanum Pseudo, Capsicum, and a begonia species developed after a few days a slight injury; and yet, sixteen species of Nicotiana, Salvia involucrata, Boston Ivy, Boston ferns, a cactus, a pineapple plant, geraniums, alfalfa, clover, and wheat seedlings, showed 'not the slightest effects from the fumigation. One must remember that these houses are not new and are of only average tightness. However, the results are significant, for they are representative of the average commercial plant. The methods of fumigation used by the writer are similar to those commonly recommended. Instead of lowering the paper bags containing the potassium cyanide, into the beakers or earthen-ware crocks by means of strings and pulleys, they were carefully dropped by hand into the acid and water. The materials used for fumigating were one part KCN (98 per cent purity), two parts (liquid measure) concentrated sulphuric acid (1.83 specific gravity), and four parts water. A 1-1-3 formula, however, was found by Woglum (8) to be very satisfactory in field practice. The acid was poured into the water, and not the reverse, as has been recommended, and still is, by occasional popular writers. The reasons for pouring the acid into the water are very obvious, for the water being much lighter spreads over the heavy acid and as soon as the steam is generated by the chemical action, the water and acid are splattered in every direction. The jars or beakers were placed at intervals of about twenty-five feet so that the diffusion of gas would be even. If possible, the receptacles should be kept a few feet from the plants, as the rising concentrated gases are liable to cause a slight injury. Although only "all night" fumigations were used in the writer's work and with success, the length of time necessary for the best results is still unsettled. In cases where large amounts of potassium cyanide are desired, the short period is of course obligatory. A question of this kind must be decided by the fumigator. Before leaving this subject, I suppose it would be imprudent not to warn the novices of the toxic properties of the hydrocyanic acid gas. One deep breath is said to be sufficient to kill a man, and although the recommended weak strengths might not cause the immediate death of a healthy individual, it is unnecessary to perform experiments in this phase of the subject. During the "all night" fumigations, most of the gas has probably disappeared through the *A gram may readily be changed to the term of an ounce by multiplying the former with 28.35; but in making such a transformation, the cubic foot of space must be multiplied with the same multiple. cracks in an average house, nevertheless, every fumigated house should be ventilated fifteen to thirty minutes before the air in it is breathed by a person. In conclusion, the following established principles should be kept in mind when fumigating greenhouses. 1. Determine the amount of hydrocyanic acid gas which is necessary to destroy the insects without injuring the plants. To find such a strength, it is advisable to commence with 0.005 gram KCN to a cubic foot of space, and if this amount is insufficient, to increase it by the addition of 0.001 gram at each subsequent fumigation (which should be at least three days apart) until the correct strength is obtained. 2. Make the house as air-tight as possible. 3. Fumigate only when the foliage and stems of the plants are dry. 4. Fumigate when the temperature and the humidity are not too high. 5. Fumigate preferably on cloudy nights following cloudy days. 6. Fumigate when there is little or no wind. Succulent plants as the tomato are more easily injured by hydrocyanic acid gas than plants with tougher issue like the cucumber, and consequently, the strength of gas should vary directly with the subject treated. 8. Lock the doors and put up notices so no one can enter the house accidentally. (1) SELECTED BIBLIOGRAPHY. Woods, A. F., and Dorsett, P. H., U. S. Dept. of Agr., Bur. of Ent., Cir. 37, 2nd Ser. 1899. (2) Morrill, A. W., Hatch Expt. Sta. of the Mass. Agr. Col.. Tech. Bul. 1, 1903. U. S. Dept. of Agr., Bur. of Ent., Cir. 57, 1905, (3) (4) (5) (5) Houghton, C. O., Del. Col. Agr. Expt. Sta. Rpt. 18: 85-88, 1906. Tower W. V., Mass. Agr. Expt. Sta., Pt. 1, Rpt. 22: 214-227, 1910 (issued. Hooker, C. W., Mass. Agr. Expt. Sta. Pt. 1. Rpt. 22: 227-247, 1910 (issued). (6) Constantin, Gerome, and Labroy, Gard. Chron. Vol. 35, 3rd. Ser. p. 328, 1904. (7) (8) Woglum, R. S., U. S. Dept. of Agr., Bur. of Ent.. Bul. 90, Pt, 2, 1911. WINTER INJURY TO FRUIT BUDS OF THE APPLE AND PEAR.* BY O. B. WHIPPLE, Montana Experiment Station, Bozeman, Montana. While the abundance of data upon winter injury to buds of stone fruits suggest that such injury is not uncommon, the lack of data upon the occurrence of such injury to pomaceous fruits naturally leads one to think that the dormant fruit buds of such plants are seldom injured in winter. In some sections of Montana, the winter of 1910-11 was especi *See Bulletin No. 91, Montana Agr'l Expt. Station. |