UNIVERSITY OF CALIFORNIA 
 
 AGRICULTURAL EXPERIMENT STATION 
 
 E. W. HILGARD, DIRECTOR 
 
 ORCHARD FUMIGATION 
 
 C. W. WOODWORTH 
 Entomologist 
 
 The Cottony Cushion Scale 
 against which fumigation was first practiced 
 
 BULLETIN 122 
 
 BERKELEY 
 
 Zbe THntvevsit£ {press 
 
 January, 1899 
 
ORCHARD FUMIGATION.* 
 
 By C. W. Woodworth. 
 
 The fumigation of orchards has never been practiced in California 
 outside of the seven southern counties, and there only in the citrus 
 belt. It has supplanted spraying almost entirely in much of this 
 region, however, and there seems to be no reason why it should not 
 be found equally satisfactory in other parts of the State. 
 
 Though much has been written on this subject there is nothing that 
 gives a comprehensive account of the methods now in use. This 
 bulletin has been prepared to supply this information and to awaken, 
 a wider interest in the matter of fumigation. The experience with 
 fumigation in the East emphasizes its value as a means of utterly 
 destroying newly introduced scale insects; and there is greater reason 
 for hope to entirely eradicate such insects with this process than by 
 any other known method except the destruction of the infested trees. 
 
 Without any question, the most thoroughly effective of all the 
 insecticides which have been applied to plants is hydrocyanic acid 
 gas. The discovery of its value and the development of the method 
 of its application forms one of the most interesting chapters in 
 economic entomology. But for the ravages of the cottony cushion 
 scale the process might never have been discovered, and had not the 
 red scale become very destructive it might have been cast aside as 
 impractical; it required the invasion of San Jose scale to carry the 
 method into the Eastern States. 
 
 Historical. 
 
 As introductory to the review of our present methods it will be 
 advantageous to outline briefly the history of their discovery and 
 development. The cottony cushion scale which was introduced into 
 California from Australia, many years ago, gradually spread over the 
 State, reaching Southern California about twenty years ago; and after 
 a few years had so increased as to threaten the very existence of the 
 citrus orchards in that region. Almost driven to despair, the growers 
 made a very urgent appeal to the United States Entomologist, Professor 
 Riley, who detailed two assistants to undertake the study of the 
 methods of controlling the insect. One of these was Mr. D. W. 
 Coquillett, whose name will always be associated with orchard fumiga- 
 tion as the first discoverer of the value of h3 T drocyanic acid gas for 
 this purpose. 
 
 *A resume of this bulletin will be found on page 33. Most of the figures are from photographs 
 taken for this bulletin by Mr. J. W. Mills of the Station at Pomona. Fig. 12 is from the Report of 
 the State Board of Horticulture, and Fig. 13 from Bulletin 57 of the Maryland Agricultural Experiment 
 Station. 
 
The Department of Agriculture had no part in the discovery of 
 the value of this method, for after employing Mr. Coquillett for some 
 six months, during which time he experimented with various sprays, 
 he was "laid off" owing to an insufficient appropriation. Mr. Coquillett 
 continued to work on the problem of destroying the scale, though at 
 his own expense, and finally in September, 1886, he began seriously to 
 study the methods of fumigation. These had been inaugurated by 
 various parties, prominent among whom were Mr. J. W. Wolfskill and 
 his very able foreman Mr. Alexander Craw. At their place Mr. 
 Coquillett began his experiments, profiting by the work already done 
 by these gentlemen and by the facilities here provided, and here he 
 first conceived the idea of using hydrocyanic acid gas. Some six 
 months were devoted to the perfecting of the method, which they 
 hoped to patent and profit by, and it was therefore guarded as a 
 profound secret. 
 
 Mr. Coquillett did not give to the world the knowledge of the value 
 of hydrocyanic acid gas, but it came from another discovery which 
 resulted through the public spirit of certain growers. The success of 
 fumigation at the Wolfskill place became widely known, and those who 
 .were seeing their trees die from the effect of the scale were naturally 
 impatient to know a remedy. Finally, a number of growers about 
 San Gabriel appealed to Professor Hilgard and asked for a chemist to 
 experiment with gases to find out what would best effect the results 
 desired. Mr. F. W. Morse was delegated for this work and found, 
 like Mr. Coquillett, that hydrocyanic acid gas was by far the most 
 satisfactory. In the course of these experiments certain parties 
 who had witnessed some of the former experiments, recognized the 
 odor of the gas, and thus the secret that was so jealously guarded 
 became known to the public. The honor of making known the value 
 of this insecticide thus lies with Mr. Morse and Professor Hilgard, 
 under whose directions the experiments were made. 
 
 The experiments conducted by Mr. Morse were reported by him in 
 Bulletin 71 of this Station, and thus vanished for Mr. Coquillett both 
 the honor and hope of profit from the discovery made six months before. 
 Mr. Coquillett, however, continued to experiment, becoming again an 
 assistant in the Department of Agriculture, and did more than any 
 other person to develop and perfect our present methods of fumigation. 
 
 Injury to Foliage'. — The problem of fundamental importance in 
 fumigation is that of preventing injury to the plant. It is not a hard 
 matter to kill an insect with almost any chemical, if used strong 
 enough; but to do this, without also at the same time injuring the tree, 
 is often a difficulty that cannot be overcome. This difficulty has been 
 the chief one to contend against in perfecting the method of fumiga- 
 ting with this gas. 
 
 The first method by which the reduction of injury was accomplished 
 was the soda process of Morse, which consisted in adding ordinary 
 baking soda to the cyanide solution, using something like two and a 
 half times as much soda as there is cyanide in the solution, the result 
 being the production of carbonic acid gas, thus diluting the hydrocyanic 
 acid gas. 
 
 Previous to the time of the publication of this method Mr. 
 
Coquillett accomplished a similar diminution of the injury, by the 
 slow generation of the acid, which he accomplished by means of a 
 generator consisting of two parts, from one of which the sulphuric 
 acid passed in a fine stream, regulated by a stopcock, into the other 
 containing dry cyanide. This was made known through a paper, by 
 Mr. Alexander Craw, read before a meeting of fruit growers held at 
 Los Angeles in October, 1887. 
 
 A third plan was soon devised by Mr. Coquillett, called by him the 
 "dry gas process," which consisted in passing the gas from the 
 generator through sulphuric acid before allowing it to come in contact 
 with the foliage. In this he followed Morse's idea of using a solution 
 of cyanide. This was the situation at the time of the publication of 
 Mr. Coquillett' s first paper, wherein these three processes were de- 
 scribed quite fully, as here outlined. He strongly recommended his 
 last process as the cheapest and most convenient; and Mr. Morse, in a 
 later paper, practically abandoned his soda method in favor of the dry 
 gas process. 
 
 The reasons for the injury have been, from the first, matters for 
 speculation and controversy, and even to-day it must be confessed that 
 we are far from possessing sufficient data to enable us to solve any 
 considerable part of the problem. From the first the results have 
 been very uncertain, proving that there are a number of factors 
 involved. One of the earliest to be suggested was that faulty dis- 
 tribution of the gas would tend to cause burning wherever the pure 
 or slightly diluted gas came in contact with the leaves. The experi- 
 ence in the field bore out this idea, so that in most of the earlier work 
 elaborate provision was made for the mixing of the gas and the air 
 contained in the tent. These provisions were generally some form of 
 blower connected with the generator. Later work has demonstrated 
 that this is of minor importance. 
 
 Mr. Coquillett 7 s first theory was that the mixing or perhaps the 
 combination of the gas with water rendered it more injurious, and 
 both of his processes were based on this idea; he explained the 
 effectiveness of the soda process as arising from the affinity of the 
 carbonic acid for water. 
 
 Mr. Morse's original ideas are not made plain in his writings, but 
 his later studies led him to believe that the development of ammonia in 
 the gas was the most important cause of injury. The injurious effects of 
 ammonia are well known, and he demonstrated the presence of ammonia 
 in the gas, especially in that generated from a solution of cyanide. 
 Thus we have two theories accounting for the good effects of the 
 methods then known, and both agreed in favoring the dry gas process. 
 The latter theory seems to have had more foundation in fact, but it 
 soon became evident that there were other still more important factors 
 determining the injury to the foliage. 
 
 The results, as regards the injury to the trees, continued to be 
 unreliable to a certain degree, and this fact, coupled with the wonder- 
 fully promising results of the importation of ladybirds from Australia, 
 caused the method to be laid aside to a good extent. 
 
 Fumigation for Red Scale. — The revival of the interest in fumigation 
 arose from the fact that the red scale soon became very troublesome in 
 
Orange County. Mr. Coquillett was invited to conduct experiments 
 in the orchard of Mr. A. D. Bishop with his apparatus, and here great 
 steps were made towards the perfection of the method. 
 
 The Most Destructive Scale Insects in California. 
 
 Fig. 1.— The Black Scale on Lemon, 
 
 Fig. 2.— The Red Scale on Lemon. 
 
 Here was tried the generation of the gas in a simple generator be- 
 neath the tent, and the production of the gas according to the formula 
 now in use, and better results were obtained than had hitherto been 
 known. Both Mr. Coquillett and Mr. Bishop claim to have originated 
 the changes, but we will not attempt to decide where the honor 
 belongs. 
 
 All who had tried fumigation had noticed that the trees were more 
 injured during the middle of the day than at other times, and it was 
 usually attributed to the heat in some way causing the gas to act on 
 the foliage; but at this time Mr. Coquillett began to work on the 
 theory that it was the actinic rather than the heat rays of the sun that 
 produced this effect, and a black tent was used in the work on Mr. 
 Bishop's place, which confirmed him in this idea. The idea seems to 
 have been first suggested by Mr. Bishop, judging from the subsequent 
 decision of the Commissioner of Patents, though Mr. Coquillett claims 
 to have originated it. At any rate Mr. Bishop was the first, who, 
 acting on this theory, inaugurated night work, upon, as he claims, 
 the suggestion of his wife; but Mr. Coquillett claims to have 
 stated to Mr. Bishop that better results would be obtained by night 
 work. It will not be necessary to enter further into this controversy, 
 and it will be sufficient to point out that at that time in the orchard of 
 Mr. Bishop there were originated three items that form the foundation 
 of the present practice of fumigation in California, the formula, the 
 method of generating, and the night work. 
 
 Whether the theory upon which night work was tried is correct or 
 not it would be difficult to decide, but in practice such uniform and 
 satisfactory results have followed its adoption that it is regarded as 
 essential to good fumigation. The success of the idea, and the council 
 of his neighbors, led Mr. Bishop, in company with them, to apply for 
 a patent, which was granted in spite of the vigorous protests of Mr. 
 Coquillett and Professor Riley, communicated to the Commissioner of 
 Patents by the Assistant Secretary of Agriculture. The courts, how- 
 ever, later declared the process unpatentable, and thus ended the 
 second attempt to control the process for profit. 
 
The Tent. — At first there was a great deal of diversity in the 
 construction of the tent and the means of manipulating it. It was 
 usually some form of bell shape, and generally constructed of bed tick- 
 ing, oiled after making. 
 
 The Wolfskill fumigator was a bell tent manipulated by a derrick 
 mounted on a wagon, and having an arm on each side extending over 
 the tops of the trees when driven between the rows. The tent was 
 lifted by means of a rope attached to the top and extending to a loop 
 at the end of the arm of the derrick, through which the tent was drawn 
 as it was removed from the tree. It is illustrated in the Report of the 
 United States Department of Agriculture for 1887. 
 
 The Titus fumigator was a similar tent, but supported by a large, 
 square frame with braced legs at each corner, mounted on wheels, and 
 with a piece across the top, on which the tent could be wound in 
 removing it from a tree. This is also shown in the above-named report. 
 
 The Culver fumigator consisted of two light frames having the 
 shape of a half-bell and covered with a cloth, forming a complete 
 tent when closed together around a tree. This is also figured in the 
 report mentioned above, but it was later simplified and the cloth 
 allowed to rest on the sides of the tree. 
 
 These were all provided with the old generators with blowers, and 
 have all been replaced by better tents as described below in this 
 bulletin. 
 
 The Dose. — Of fundamental importance is the quantity of chemi- 
 cals to be used. This has been a matter of considerable variation, and 
 because of its importance will be discussed quite fully. The original 
 table given by Morse, but with the addition of a column giving the 
 amount of dry cyanide, is as follows: 
 
 Size of 
 
 Cyanide of 
 
 (Equivalent to 
 
 Bi-Carbonate 
 
 Sulphuric 
 
 Tree. 
 
 Potassium. 
 
 Dry Cyanide.) 
 
 of Soda. 
 
 Acid. 
 
 Feet. 
 
 Fluid Ounces. 
 
 Ounces. 
 
 Pounds. 
 
 Fluid Ounces. 
 
 4 
 
 .7 
 
 .28 
 
 .05 
 
 .4 
 
 5 
 
 1.6 
 
 .64 
 
 .11 
 
 .9 
 
 6 
 
 2.5 
 
 1.0 
 
 .20 
 
 1.3 
 
 7 
 
 4.0 
 
 1.6 
 
 .29 
 
 2.1 
 
 8 
 
 6.0 
 
 2.4 
 
 .44 
 
 3.1 
 
 9 
 
 8.5 
 
 3.4 
 
 .63 
 
 4.5 
 
 10 
 
 11.5 
 
 4.6 
 
 .87 
 
 6.2 
 
 11 
 
 15.5 
 
 6.2 
 
 1.14 
 
 8.2 
 
 12 
 
 20.0 
 
 8.0 
 
 1.50 
 
 11.6 
 
 13 
 
 25.4 
 
 10.16 
 
 1.90 
 
 13.5 
 
 14 
 
 31.6 
 
 12.64 
 
 2.50 
 
 16.6 
 
 15 
 
 39.2 
 
 16.48 
 
 2.92 
 
 20.7 
 
 16 
 
 47.5 
 
 19.0 . 
 
 3.55 
 
 25.2 
 
 17 
 
 57.5 
 
 23.0 
 
 4.23 
 
 30.1 
 
 18 
 
 67.7 
 
 27.08 
 
 5.05 
 
 35.8 
 
 19 
 
 70.9 
 
 28.36 
 
 5.93 
 
 42.1 
 
 20 
 
 90.5 
 
 36.2 
 
 6.93 
 
 49.2 
 
 The latter-half of the table is by no means accurately calculated, 
 and is probably safest between eight and twelve feet. The table was 
 calculated for trees about as broad as high, such as naval oranges. 
 
8 
 
 Mr. Coquillett gave the same year the following amounts of chemicals: 
 
 
 
 
 
 In Dry Ga 
 
 s Process. 
 
 
 Height 
 
 Diameter 
 
 Cyanide 
 
 Sulphuric 
 
 
 
 
 (Equiv. to 
 
 of Tree. 
 
 of Tree. 
 
 Solution. 
 
 Acid. 
 Fluid Ounces. 
 
 Sulphuric 
 Acid. 
 
 Bi-Caebonate 
 
 of Soda. 
 
 Dry 
 Cyanide.) 
 
 Feet. 
 
 Feet. 
 
 Fluid Ounces. 
 
 Fluid Ounces. 
 
 Ounces. 
 
 Ounces. 
 
 6 
 
 5 
 
 2 
 
 li 
 
 If 
 
 H 
 
 li 
 
 10 
 
 10 
 
 12 
 
 7 
 
 11 
 
 11 
 
 n 
 
 12 
 
 8 
 
 9 
 
 5 
 
 8 
 
 8 
 
 3i 
 
 16 
 
 12 
 
 28 
 
 16 
 
 25 
 
 27 
 
 m 
 
 20 
 
 14 
 
 47 
 
 26 
 
 40 
 
 43 
 
 * 
 
 We do not understand exactly the method of calculating this table, 
 but it uses distinctly more chemicals than the previous one. These 
 are the tables given in the Report of the State Board of Horticulture, 
 printed in 1888. 
 
 In 1889, Mr. Coquillett gave another table, according to the new 
 formula developed by the work in Orange County, and is the first one 
 for that formula. The table is as follows: 
 
 Height of 
 
 Diameter of 
 
 Cyanide of 
 
 Water. 
 Fluid Ounces. 
 
 Sulphuric 
 
 Tree. 
 
 Tree. 
 
 Potassium. 
 
 Acid. 
 
 Feet. 
 
 Feet. 
 
 Ounces. 
 
 Fluid Ounces. 
 
 10 
 
 8 
 
 2i 
 
 41 
 
 2i 
 
 12 
 
 10 
 
 41 
 
 9 
 
 4*. 
 
 12 
 
 14 
 
 81 
 
 m 
 
 81 
 
 14 
 
 10 
 
 54 
 
 ii 
 
 51 
 
 14 
 
 12 
 
 n 
 
 15 
 
 1\ 
 
 16 
 
 14 
 
 12 
 
 24 
 
 12 
 
 18 
 
 14 
 
 15 
 
 30 
 
 15 
 
 The amounts given in this table are from a quarter to a third less 
 than for the former process, and somewhat less than the Morse table. 
 
 The next table to appear was the one given by Mr. Craw in his 
 pamphlet on Destructive Insects, and is as follows: 
 
 Height of 
 Tree. 
 
 Diameter 
 
 THROUGH 
 
 Foliage. 
 
 Water. 
 
 Sulphuric 
 Acid. 
 
 Cyanide of 
 Potassium. 
 
 Feet. 
 
 Feet. 
 
 Fluid Ounces. 
 
 Fluid Ounces. 
 
 Ounces. 
 
 6 
 
 4 
 
 2 
 
 1 
 
 1 
 
 8 
 
 6 
 
 4 
 
 2 
 
 2 
 
 10 
 
 8 
 
 6 
 
 3 
 
 3 
 
 12 
 
 10 
 
 10 
 
 5 
 
 5 
 
 12 
 
 14 
 
 14 
 
 7 
 
 7 
 
 14 
 
 14 
 
 16 
 
 8 
 
 8 
 
 16 
 
 16 
 
 18 
 
 9 
 
 9 
 
 18 
 
 16 
 
 20 
 
 10 
 
 10 
 
 20 
 
 16 
 
 22 
 
 11 
 
 11 
 
 22 
 
 18 
 
 24 
 
 12 
 
 12 
 
 24 
 
 20 
 
 26 
 
 13 
 
 13 
 
 26 
 
 20 
 
 27 
 
 m 
 
 134 
 
 30 
 
 20 
 
 28 
 
 14 
 
 14 
 
This table is the most faulty, in its calculations, of any that have 
 appeared, for the amounts of chemicals given varies as the vertical 
 section of the tent and not as its cubical contents. It is, therefore, 
 much too strong for the smaller trees and too weak for the larger. 
 
 Mr. T. B. Johnson, who superintended the fumigation work of the 
 San Diego County Horticultural Board, adopted a table which appeared 
 in the report of the State Board of Horticulture for 1894, as follows: 
 
 Height of 
 Tree. 
 
 Diameter 
 through 
 Foliage. 
 
 Water. 
 
 Sulphuric 
 Acid. 
 
 Cyanide of 
 Potassium. 
 
 Feet. 
 
 Feet. 
 
 Fluid Ounces. 
 
 Fluid Ounces. 
 
 Ounces. 
 
 6 
 
 4 
 
 3 
 
 li 
 
 1 
 
 8 
 
 6 
 
 6 
 
 21 
 
 2 
 
 10 
 
 8-10 
 
 12-15 
 
 4-5 
 
 31- 41 
 
 12 
 
 10-14 
 
 18-26 
 
 6-8f 
 
 5-7 
 
 14 
 
 12-14 
 
 26-30 
 
 81-10 
 
 7-8 
 
 16 
 
 14-16 
 
 33-37 
 
 11 -121 
 
 9 -10* 
 
 20 
 
 16-18 
 
 48-56 
 
 16 -18f 
 
 13 -15 
 
 24 
 
 18-20 
 
 67-75 
 
 221-25 
 
 18 -20 
 
 This table is based on the preceding one, indeed is practically the 
 same, but contains, as stated, increased doses for the larger trees where 
 the former table was most in error. The plan of calculating both 
 tables is entirely wrong; and it is not strange that with this table to 
 follow, fumigation should have fallen into some disrepute in San 
 Diego County. 
 
 In Bulletin No. 115 of this Station the following table is given: 
 
 
 Height 
 
 of Tree. 
 
 Amount of Cyanide of Potassium. 
 
 If as broad as 
 high (Navel 
 Oranges, etc.) 
 
 6 feet. 
 
 8 feet. 
 10 feet, 
 12 feet. 
 15 feet. 
 19 feet, 
 
 If § as broad as 
 high (Seedling 
 Oranges, etc.) 
 
 1 ounce 
 
 1 ounce 
 
 2 ounces 
 
 4 ounces 
 
 8 ounces 
 
 1 pound 
 
 8 feet, 
 10 feet. 
 12 feet. 
 15 feet, 
 20 feet. 
 28 feet. 
 
 The calculation of the above table is correct, but the amounts given 
 are altogether below the present practice of most California fumigators; 
 some, including the most successful, use nearly twice as much. It 
 was not prepared as the result of original work, but rather as a 
 re-calculation of the average of the two preceding tables. 
 
 The latest table that has been published is that calculated by 
 Professor Johnson of the Maryland Station, based on his work on the 
 San Jose scale. It is as follows: 
 
10 
 
 Height op Tree. 
 
 Diameter. 
 
 Cyanide. 
 
 Acid. 
 
 Water. 
 
 Feet. 
 
 Feet. 
 
 Grams. 
 
 Ounces. 
 
 Ounces. 
 
 4 
 
 3 
 
 6.17 
 
 .32 
 
 .48 
 
 5 
 
 4 
 
 12.82 
 
 .67 
 
 1 
 
 6 
 
 4 
 
 18.85 
 
 1 
 
 1.05 
 
 7 
 
 4 
 
 26.75 
 Ounces. 
 
 1.41 
 
 2.11 
 
 7 
 
 5 
 
 1.11 
 
 1.66 
 
 2.49 
 
 8 
 
 4 
 
 1.30 
 
 1.95 
 
 2.92 
 
 8 
 
 5 
 
 1.50 
 
 2,25 
 
 3.39 
 
 9 
 
 5 
 
 1.96 
 
 1.94 
 
 4.41 
 
 9 
 
 6 
 
 2.24 
 
 2.36 
 
 5 
 
 10 
 
 7 
 
 3.20 
 
 4.08 
 
 7.02 
 
 10 
 
 8 
 
 3.62 
 
 5.43 
 
 8.14 
 
 11 
 
 7 
 
 3.95 
 
 5.92 
 
 8.88 
 
 11 
 
 8 
 
 4.40 
 
 6.60 
 
 9.90 
 
 12 
 
 9 
 
 5.88 
 
 8.82 
 
 13.23 
 
 12 
 
 10 
 
 6.51 
 
 9.76 
 
 14.65 
 
 13 
 
 9 
 
 6.93 
 
 10.39 
 
 15.58 
 
 13 
 
 10 
 
 7.65 
 
 11.47 
 
 17.26 
 
 14 
 
 11 
 
 9.76 
 
 14.64 
 
 21.96 
 
 14 
 
 12 
 
 10.65 
 
 15.97 
 
 23.45 
 
 15 
 
 11 
 
 13.28 
 
 16.42 
 
 29.88 
 
 15 
 
 12 
 
 14.24 
 
 21.36 
 
 32.04 
 
 16 
 
 14 
 
 16.34 
 
 24.51 
 
 36.76 
 
 16 
 
 15 
 
 17.53 
 
 26.27 
 
 39.43 
 
 17 
 
 14 
 
 18.39 
 
 27.57 
 
 41.35 
 
 17 
 
 15 
 
 19.36 
 
 29.40 
 
 44.23 
 
 18 
 
 15 
 
 22.06 
 
 33.09 
 
 49.63 
 
 19 
 
 16 
 
 26.10 
 
 39.15 
 
 58.72 
 
 20 
 
 16 
 
 29 
 
 43.05 
 
 65.25 
 
 The above table is accurately made, but the amounts are very much 
 greater than used in this State. 
 
 In order to compare the above tables, the cubic contents of the tents 
 of the various dimensions given were calculated.* 
 
 The following table gives the results thus obtained: 
 
 Date. 
 
 Name. 
 
 Capacity per Ounce of Cyanide. 
 
 1887 
 
 F. W. Morse 
 
 145 cubic feet 
 
 1888 
 
 D. W. Coquillett 
 
 95 cubic feet 
 
 1889 
 
 D. W. Coquillett 
 
 165 cubic feet 
 
 1891 
 
 Alexander Craw 
 
 352 cubic feet 
 
 1894 
 
 T. B. Johnson 
 
 242 cubic feet 
 
 1896 
 
 C. W. Wood worth 
 
 300 cubic feet 
 
 1898 
 
 W. G. Johnson 
 
 80 cubic feet 
 
 It is interesting to notice that the best practice in this State at the 
 present time is scarcely at all different, in the amount of cyanide used, 
 
 * The manner of calculation is as follows : The top portion of the tent was considered a hemi- 
 sphere and the lower portion a cylinder. The formula is 7T r 2 (h—hr) in which h is the height of the 
 tent and r one-half of the diameter. The average capacity of the tents in each table was thus 
 determined and compared with the average dose. 
 
11 
 
 from the formula originally published by Mr. Morse in Bulletin 71 of 
 this Station. 
 
 The Present Practice. 
 
 Having followed the changes through which the process has 
 passed, we must consider in detail the apparatus and plan of procedure 
 used at the present time. There is, of course, no absolute uniformity, 
 for every outfit is made or handled in a somewhat different manner in 
 some of its details. 
 
 The Canvas. — Common duck is now uniformly employed for mak- 
 ing the tent, most of them being made of the 8-ounce canvas, such as 
 is used for light sails. The cloth is lapped and double-sewed in the 
 same manner as for tents or sails. The edge is usually simply 
 hemmed, but some bind it with rope. Whenever permanent rings for 
 handling are attached, the tent is reinforced, but this is a matter in 
 which there is much diversity. The details of the construction will 
 depend somewhat on the size and kind of tent, and will be referred to 
 again, below. 
 
 After the tent is made, it is treated in some manner to make it 
 gas-tight, so as to confine the gas better. Three methods are used for 
 this purpose, all of which seem to give good satisfaction. 
 
 The first method is to thoroughly treat the tent with boiled linseed 
 oil. It is applied freely with a brush, and the whole cloth becomes 
 saturated with it. The tent must be kept spread out till quite dry, 
 for the oil has a great tendency to heat if not exposed freely to the 
 air, and the cloth chars and becomes rotten. If properly done, the tent 
 remains strong and tight, and is not too stiff. 
 
 The second method consists in the use of sizing and paint. The 
 sizing is applied in the same manner as the oil, and penetrates the fiber 
 of the cloth in the same way. As soon as this coat is dry it is 
 followed by another of rather thin flexible paint, sometimes on both 
 sides; the result being a perfectly tight tent with a very smooth sur- 
 face and fully as flexible as the oiled tent. The sizing protects the 
 fiber of the cloth, so there is no danger of heating. 
 
 The third method is the saturation of the cloth by a decoction of 
 the chopped-up leaves of the common prickly pear cactus {Opuntia 
 engelmani.) This decoction is made by filling a barrel two-thirds full 
 of the chopped stems, adding cold water till the barrel is nearly full; 
 then letting it soak twenty-four hours, when it is drawn off and 
 strained, and is ready for use. This decoction is seldom used by 
 itself, but other substances are added according to the whim of the 
 person treating the tents. Very generally a pigment, like yellow ochre 
 or Venetian red, is added to give more body to the mixture; sometimes 
 glue is added also. There is some tendency in tents treated with the 
 cactus decoction, to become moldy when not in use, to prevent which 
 some prepare a tannin solution to add to the mixture. The decoction 
 may be applied to the tents with a brush, but a better way is to soak 
 them during the night in a trough containing the mixture. In the 
 morning they can be raised by means of ropes and pulleys and allowed 
 to drain for some time and then spread out to dry. Tents treated 
 with this mixture are scarcely at all stiffened and seem to be satisfac- 
 torily tight. 
 
12 
 
 The Bell Tent. 
 
 The tents known as bell tents are cylindrical in shape, with the top 
 ronnded over like a dome. They are used in connection with a der- 
 rick, by means of which they are placed upon and lifted from trees; 
 the derrick also supports the weight of the tent while it is upon the 
 tree. The bell tent was one of the original forms of tents, and while 
 mostly supplanted by other styles, is still used to a considerable extent, 
 especially for very large trees. It is the only form of tent now in use 
 where the whole weight of the tent is not carried by the tree, and 
 many favor it for this reason. 
 
 The derrick used with the bell tents at the present time is that used 
 with the Preble fumigator, or some modification of it. This is shown 
 in Fig. 3. It consists of a wagon, which supports a mast considerably 
 
 The Bell Tent. 
 
 Fig. 3. — Derrick with one tent nearly in place on a tree, 
 and the other drawn up ready for moving. 
 
 higher than the trees to be fumigated, and is braced at the bottom with 
 stays that hold it rigidly in place. Across the top of the mast a yard 
 is fastened and braced with trusses extending from the mast. The 
 length of the yard is about a third longer than the distance between 
 the rows of trees. Near each end of the yard are placed cross-bars as 
 shown in the illustration. The arrangement of the ropes can be under- 
 stood from a study of the figure. 
 
 The heaviest rope is attached to the top of the tent with double 
 pulleys. Along the lower edge, on the four sides of the tent, are 
 fastened boards, generally of ordinary six-inch fencing, which are 
 called trail boards, and from the center of each of these the trail 
 ropes pass upwards and over pulleys attached to the yard and ends 
 of the cross-bars. All these ropes follow the yard till near the mast, 
 then passing again over pulleys, they go down to the bed of the 
 wagon and are fastened over belaying pins. The trail ropes pass 
 
13 
 
 through thimbles along the side of the tent as well as through the 
 pulley at the center of the trail, so that when the latter is drawn up to 
 the yard or cross-bars, the sides of the tent are gathered in three or 
 four places and raised almost as high. The only other ropes are the 
 guide lines attached to the center of the trails and hanging free. They 
 are of such length as to reach the ground when the tent is elevated. 
 
 The manipulation of these tents can be readily understood from a 
 study of the engraving. While the tree is being fumigated the tent is 
 usually allowed to rest partly on the tree, and not drawn up to the 
 yard as shown in the illustration. Two persons can handle the 
 apparatus, but three or four greatly facilitate the work. The pro- 
 cedure in changing the tent is as follows: Supposing that both tents 
 are upon the trees and the time has arrived to make the change, the 
 first operation is to pull on the main rope attached to the center of the 
 tent and raise this as far as it will go easily, and then fasten the rope 
 again to the belaying pin. If short-handed, one tent is raised at a 
 time, but with plenty of help both go up at the same time. The trail 
 ropes are next taken in hand and pulled all together, and if this be- 
 comes difficult, two (or even one at a time) are pulled until the tent 
 on all sides is pulled up to the yard and cross-bars. While this is 
 going on one person (or perhaps more) is kept busy seeing that the 
 tent is clearing the tree properly. His first business is to see that the 
 edge with the trail boards is not caught inside of the tent; it should slip 
 up around outside of it. Later he will be occupied with making the 
 tent slip off the projecting branches. He can generally do this by 
 pulling on the guide lines, but on very large trees he may find a light 
 ladder necessary. The removal of the tent would be comparatively 
 easy but for the work at the ropes. After all the ropes are pulled tight, 
 including the main rope, and both tents are against the yard, the 
 apparatus is ready to shift to the next row. The wagon may be pulled 
 along by hand, or by a horse hitched to the end of the tongue. If the 
 ground is a little uneven, the apparatus can be kept from tipping over 
 by steadying it with the guide lines. Arriving at the proper position 
 between the next two trees, the first thing is to arrange the guide 
 lines in their places around the tree. The trail ropes are now released 
 and the tent is allowed to slowly descend upon the tree. While this is 
 taking place, one or more are busy with the guide lines, pulling the 
 trail boards this or that way as may be necessary to clear the branches. 
 
 If a branch is particularly spreading it may be necessary to use a 
 ladder, forcing it within the tent by hand. Should the trees be very 
 large the branches will extend over the wagon, causing much trouble 
 in pulling the tent down on that side. With a small symetrically 
 shaped tree the tent can be lowered rapidly into place without any 
 trouble whatever. After the trail ropes are all played out, the main 
 rope is loosened and the tent allowed to settle to the position desired, 
 and fastened there. There yet remains the job of seeing that the 
 tent is tight to the ground on all sides. The trail boards are made to 
 lie on the part of the tent that is on the ground, and earth is thrown on 
 any part of the edge of the tent that does not lie down well. When 
 both tents are thus in position they are ready for the "fumigator," or 
 man who charges the generator. 
 
14 
 
 The Hoop Tent. 
 
 The form most used in this State is the hoop tent, which is a devel- 
 opment from the bell tent and is of the same general shape. The 
 hoop was first used as a means of keeping the mouth of the bell tent 
 open, but it was soon discarded in favor of the trail boards. It was, 
 however, discovered that for rather small- sized tents the hoop afforded 
 a better means of handling than did the derrick. 
 
 The Small Hoop-Tent. 
 
 Fig. 4.— Throwing the tent over a tree. 
 
 Fig. 5. — Pulling down the tent. 
 
15 
 
 Fig. 6. — Ready for the Furnigator. 
 
 The hoop tents now in use range from eight to fourteen feet in 
 diameter. They are made in the same way as a bell tent, omitting, 
 however, the arrangements for suspending them, and possessing, in- 
 stead, a series of cloth loops for attaching the hoop as is shown in the 
 engraving. 
 
 The hoop is usually made of three-quarter-inch gas pipe; half- 
 inch pipe will do for the smaller sizes, but it is too weak for hoops 
 above ten feet in diameter, as it bends too easily and soon becomes 
 very crooked. To make the hoop, pipe is coupled together until the 
 proper length is reached according to the size desired, and then bent 
 into shape. The union is then made by inserting into the ends a piece 
 of iron rod a foot or less in length and just small enough to enter the 
 pipe. Holes are now drilled through the pipe and rod, and rivets are 
 inserted, thus making the joint fast. A coupling with right and 
 left-hand threads might be used instead of the rod and rivets. 
 
 
 
 Fig. 7. — Diagram illustrating the method of shifting a small hoop tent from one 
 tree to another. The letters indicate the x successive positions of the hoop as the 
 tent is first thrown off of one tree on to the ground, and then is picked up and put 
 over the next. 
 
16 
 
 The manipulation of a hoop tent varies according to its* size. 
 When the diameter of a tent is not much greater than the distance be- 
 tween the nearest branches of adjacent trees, the procedure is that 
 illustrated in the preceding diagram, Fig. 7, and depicted in Figs. 4-6. 
 
 To move such a tent from one tree to the next, two men place 
 themselves on opposite sides of it, grasp the hoop and raise the side 
 which is opposite the tree to which they intend to move it; they step 
 side- wise, dragging the side that is on the ground closer to the trunk, 
 and the hoop will be in about the position indicated by A in the dia- 
 gram. The men, still holding the hoop as they first grasped it, continue 
 to raise the free side until it passes over the top of the tree, when it is 
 allowed to fall to the ground between the two trees. In falling the 
 hoop naturally moves away from the tree from which it came, so that 
 the cloth falls over the edge of the hoop, as shown in the diagram. If 
 this does not occur, the tent is pulled into that position in order that, 
 when the hoop is raised, the center of the tent will be brought at once 
 to about the center of the top of the tree. 
 
 The men now grasp the hoop again, as before, carry it towards 
 the tree and lift up the further edge, then with one movement 
 throw it over the tree to about the position indicated by D. Often 
 it will go clear to the ground and needs no further attention. If it 
 stays at D, the men proceed to the point highest from the ground, and 
 pull on the hoop and canvas until the former rests easily on the 
 ground. The cloth which extends beyond the hoops forms a 
 sufficiently tight contact with the ground if the latter is ordinarily level. 
 
 The manipulation of the large hoop-tents differs from that above 
 described, from the fact that the proximity of the trees makes it 
 impracticable to lay the tent on the ground. The procedure in this 
 case is indicated in the accompanying diagram, Fig. 12, and by Figs. 
 
 8-11. 
 
 The Large Hoop-Tent. 
 
 : ; 
 
 X 
 
 Fig. 8. — Putting the tent on a tree. The tent in this case is being 
 lifted from the ground, and not shifted from another tree. 
 
17 
 
 The Large Hoop- Tent. 
 
 
 **ip— V 
 
 Fig. 9.— Pulling down the canvas so that the hoop 
 will rest freely on the ground. 
 
 Fig. 10. — Beginning to raise the tent. 
 
18 
 
 The Large Hoop-Tent. 
 
 Fig. 11. — Tent almost off the tree. 
 
 ■S *0 J&bL 
 
 
 
 
 I 
 
 
 _I 
 
 \d 
 
 -" "E 
 
 Fig. 12. — Diagram illustrating the method of shifting a large hoop-tent from one 
 tree to another. The letters indicate the successive positions of the hoop. 
 
 It is better to have three men to handle these tents, though two can 
 do it. When working three, two take hold in the same way as 
 described above for the small hoop-tents, and the third pulls on the 
 side that is raised to the position A. The latter then catches the hoop 
 with a fork at the end of a pole, and as the others lift he assists by 
 pushing. This is shown in Figs. 10, 11. 
 
 When the hoop has taken about the position shown at B, in Fig. 
 12, or a little past that point, the two men holding the sides of the tent 
 carry it to the next tree to the position C, and then without pausing, 
 and while the tent is full of air and streaming out behind with the aid 
 of momentum acquired, the upper edge of the hoop is forced over the 
 top of the tree and down on the other side. Generally it is possible to 
 
19 
 
 throw the hoop into the position D, when it can readily be pulled down 
 to the ground. 
 
 If there is any trouble in pulling the cloth over, the third man, hav- 
 ing tossed his pole to the next tent, goes around to the near side of the 
 tent just moved, and as the others pull on the far side, shakes the 
 cloth of the tent away from the tree, thus relieving some of the friction. 
 The weight of the hoop of these large tents greatly helps in the pro- 
 cess of slipping the cloth over the tree, the most energy being required 
 in removing the tent. The large tents are moved quite as rapidly as 
 are the smaller ones. It will be noticed that the cloth is turned inside 
 out with each change in the case of the larger tents, but with the 
 smaller ones the same side of the cloth is always next to the tree. 
 
 The Box Tent. 
 
 The latest development along this line is what is known as the box 
 tent. It is an Eastern idea devised for use on deciduous trees in 
 which the wood is less pliable and more easily broken than are citrus 
 trees. It may deserve a trial in our orchards, though, doubtless, we 
 would soon simplify the handling so as to work more rapidly than is 
 now possible. 
 
 The box tent is somewhat intermediate between the bell, or hoop 
 tent, and a sheet tent. It has something of the shape of the hoop 
 tent, but flaring beneath and without anything stiff at the bottom. It 
 is made with a square top-piece and with four sides, which are a half 
 larger at the bottom than at the top. 
 
 The manipulation of this tent is accomplished by the use of a pole 
 called the "lifter." This pole has a piece of scantling fastened to the 
 bottom and braced, as shown in Fig. 13, and in the accompanying 
 
 The Box Tent. 
 
 7 ",M 
 
 
 'M ~ * - *l» 
 
 mm* 
 
 t4^f)t/iili 
 
 Fig. 13. — Lifter in position over a tent ready to 
 remove it from the tree. 
 
20 
 
 diagram, Fig. 14. To the top of the pole is attached a guy rope and 
 a block pulley over which passes a rope for lifting the tent. A small 
 Y at a convenient height for fastening the rope completes the lifter. 
 
 F 
 
 Fig. 14. — Diagram illustrating the method of changing a box tent from one tree 
 to another by the use of the lifter. A, B, C, D, and E represent the successive 
 positions of the tent. F the lifter and G guy rope. F' G' the second position of 
 the same. 
 
 In changing the tent from one tree to another the process is to 
 place the lifter next to the tree to be uncovered. The guy rope is 
 then tied to an adjacent tree in such a manner as to allow the end of 
 the lifter to stand over the center of the tent. The end of the lifter 
 rope is fastened to the edge of the tent opposite the base of the lifter. 
 As the edge of the tent is being lifted by this rope, assistants pull the 
 edge of the tent aside, freeing the branches; small forked poles are 
 used to assist in this work. After all the branches are free the tent is 
 lowered to the ground beside the tree. 
 
 The lifter is now moved to the tree to which the tent is to be 
 placed, as shown at C. By pulling on the lifter rope, the edge of the 
 tent is raised again to the top of the pole, when the rope is fastened. 
 Two persons now take hold of the edges of the tent and pull them 
 around the tree, while a third pulls on the guy rope till the top of the 
 tent is over the top of the tree, when the tent is lowered and pulled 
 into position. The movement of the lifter by means of the guy rope 
 is not indicated in the drawing, but can be readily understood with- 
 out. The same movement is useful in untenting a tree. 
 
 After letting the tent down over the tree the lifter rope is untied 
 and the bottom of the tent pushed up towards the tree and made to lie 
 close to the ground. If necessary, a little earth is thrown upon it to 
 
 hold it down. 
 
 The Sheet Tent. 
 
 The form that seems most likely to replace all others is the sheet 
 tent. It is the simplest to make, the most readily adaptable to all sizes 
 of trees, and is almost as readily moved from tree to tree as the hoop 
 tent. It contains, however, a great deal of useless canvas, which is an 
 objection to the economical mind. 
 
21 
 
 Sheet tents are made either in a regular or in an ova.1 hexagon, and 
 perfectly flat. A pair of rings is often attached on each side, near 
 what is intended as the front edge; it is convenient to attach these 
 rings by iron links, so that they can be rattled and found in the dark 
 by shaking the tent. 
 
 The movement of the tent is accomplished by the use of two poles. 
 These are usually simple poles with a small rod projecting from the 
 upper end, over which the ring of the tent is slipped, a rope is also 
 fastened at the upper end. The length of the pole is slightly greater 
 than the height of the trees it is desired to cover. Sometimes the pole 
 has the same shape as the lifter used for the box tents, but the pulleys 
 and guy ropes are not needed, except for the largest trees. 
 
 The ordinary process of moving the sheet tent is shown in Figs. 
 16-19 and by the accompanying diagram Fig. 15. A bird's-eye view 
 
 
 
 ' IvtfS' 
 
 
 h 1 
 
 
 
 
 
 
 .!__, 
 
 m 
 
 Fig. 15.— Diagram illustrating the method of shifting a sheet tent from one tree 
 to another. The letters represent the successive positions of the end of the pole. 
 
 The Sheet Tent. 
 
 Fig. 16.— Beginning to lift the edge of the tent. 
 
99 
 
 The Sheet Tent. 
 
 Fig. 17.— Tent partly over the next tri 
 
 Pig. 18. — Tree almost covered, pole falling. 
 
23 
 
 The Sheet Tent. 
 
 Fig. 19.— Adjusting the bottom of the tent. 
 
 is also shown in Fig. 20. The men approach the tent to be moved, 
 poles in hand, and finding' the rings insert the small rods at the end 
 of the poles and take a hitch with the rope over the ring to prevent 
 the latter from slipping off. They then proceed to the other end of 
 their poles, which they have placed even with the trunk on opposite sides 
 of the tree to which the tent is to go. While taking this station they 
 have not let go of the rope, but have held it tight enough not to loosen 
 the tent ring. The next step in the process is to place one foot on 
 the end of the pole, to prevent it from slipping, and to pull on the 
 rope. This will lift up the edge of the tent as shown at A in Fig. 15. 
 As the men continue to pull on the rope the end attached to the tent 
 moves through the arc indicated by the line of arrows. As soon as the 
 pole becomes nearly enough upright, as not to slip when the foot is 
 removed from the end, the man backs off, away from the tree, and 
 thus gets a more direct pull on the tent which by this time has begun 
 to require some considerable effort. This becomes necessary also in 
 order that the pull from each side may stretch out the front edge of 
 the tent so that it may clear the top of the tree. 
 
 The tent is now spread out over two trees and reaches the ground on 
 either side. As the men at the ropes continue to back away the tent 
 is slipped from one tree to the next and the poles fall to the ground. 
 In this last stage in the process care must be taken that both poles 
 reach the ground at about the same time. If this is not done the tent 
 will shift to the side of the pole which first reaches the ground, and if 
 that side is pulled very much too fast the tent may not reach the 
 ground on the opposite side, and sheet tents are rather harder to adjust 
 than other kinds. This same difficulty, in regard to the front and back 
 ends of the tent, often occurs when using a tent barely large enough for 
 the tree . If the tent is pulled too slowly the poles will slip when the 
 
24 
 
 tent is not quite over, and the front will not reach the ground; and on 
 the other hand, if it is pulled too rapidly, the tent will go too far, and 
 the back end be free from the ground. The oval tent was made to 
 overcome this difficulty, for with it care only need be taken to slide the 
 tent far enough. 
 
 When using a large tent for a very small tree the tent is pulled up 
 so as to have sufficient slack canvas to go over the tree, and this is 
 pulled over by hand. When being removed, the cloth is pulled back 
 in the same manner as it was put on, and dragged along the ground to 
 the next tree. 
 
 In the case of very large trees, which require the lifter style of pole, 
 the process is as follows: The poles are set up and the guy ropes 
 attached as described for the box tent, only that two poles are used. 
 The other ropes are now attached to the tent at the near edge and the 
 latter pulled to the top of the pole. The rope is then made fast, the 
 guy ropes pulled, and the tent slid in the same manner as with smaller 
 tents. Sometimes the pole is not set at such an angle but nearer the 
 tent, when it will be necessary, after sliding the tent part of the way, 
 to again tie the guy rope and lift the bottom of the pole over; it will 
 then be opposite the trunk, and the tent will be lifted high enough 
 when it is given the final shift. 
 
 When there is fear of breaking the branches in removing a tent, 
 the practice is to "skin it off," using a pole of the lifter pattern, 
 and carry the rope around to the far side and attach it to the edge 
 of the tent there. The tent by this method slides over itself and 
 saves the tree to that extent; it is pulled over on to the next 
 tree as in the preceeding methods. Since much of the tent by this 
 method falls to the ground, it is harder on the tree while it is being 
 tented. By this process the tent is reversed each time it is changed. 
 
 Procedure. 
 
 The cost of fumigation, and therefore the profit in its use, 
 depends in a great measure upon the arrangement of details, 
 especially in the economical use of time. This is more important 
 than in the case of most methods for killing insects, because of the 
 time, forty minutes, required for the operation of the gas. Fumiga- 
 tion may be economically done in one of two ways; with a small 
 outfit arranged to fit in with other work, or with a large number of 
 tents sufficient to keep all hands busy. 
 
 Work with a small outfit can be arranged so as to waste but little 
 time. Fortunately, the tent may even be left on all night without 
 danger, if desired, so that a strict record of the time is not 
 necessary, only that it be not too short. A good arrangement is as 
 follows: The tents are placed on at the close of the day's work; they 
 are changed after supper, and again just before bed-time, leaving them 
 on till morning, care being taken to pull them off before the sun gets at 
 them. This will give three fumigations each night. 
 
 Large outfits are so expensive that the owner generally feels like 
 keeping them in operation all night, though some are used only in the 
 evening. The number of tents necessary will depend on the size of 
 the tent and the number of the men. The smallest number of men 
 that can work to advantage is two; they could handle perhaps twenty 
 
25 
 
 tents of medium size. This would allow two minutes for each tent, 
 which ought to be sufficient to change the tent and introduce the 
 chemicals. It is doubtful, however, if the fumigator should take part 
 in the vigorous physical work of changing the tents where so much 
 depends on his judgment. 
 
 The number generally employed in a fumigating gang is four or 
 five, according to the size of the trees. One man introduces the 
 chemicals, another looks out for the generator and measures the acid, 
 and two or three handle the tents. Such a gang can handle from 
 thirty to forty medium sized tents and cover four to six acres of 
 orchard in a night. 
 
 There is much variation in the detail of procedure in fumigating; 
 one of the best methods is illustrated in the accompanying diagram, 
 Fig. 20. It is intended to represent a gang of four working with 
 
 Up 
 
 I, ^«^<r- / 
 
 
 
 ^^ 
 
 
 
 tm. 
 
 
 
 km 
 
 Fig. 20.— Bird's-eye view of a young orchard being fumigated under sheet tents. 
 F the Fumigator. H the Helper who carries the generators and measures the acid, 
 R and L the tent men. The arrow lines indicate the path traversed by each of 
 these parties. 
 
 sheet tents in an orchard of rather small trees. Three trees are shown 
 newly covered, one tent in the process of being shifted, and three 
 others ready to have the tents removed. The four dark spots indicate 
 the position of the men at the time the fumigator is about to go under 
 the tent, and the lines of arrows show the paths over which the men 
 will travel during the next minute. The fumigator enters the tent 
 (Fig. 21), introduces the chemicals and quickly withdraws, sees that 
 the tent is down tightly to the ground, and picks up his tray of 
 cyanide and proceeds to the next tree. The helper holds up the edge 
 
26 
 
 of the tent while the fumigator enters, and drops it as he comes out, 
 then turning he chirps to the horse in the acid wagon and drives along 
 to the next tree. He next removes the generator from beneath this 
 tree, pours out the contents (already used) on the ground, measures 
 out the water and then the acid according to the directions of the fumi- 
 gator. (Fig. 22. ) He then carries the generator to the fumigator who 
 is waiting by the next tent. 
 
 The Acid Wagon. 
 
 Fig. 21. — The helper in the act of measuring the acid in a graduate. A 
 generator is shown on the shelf below the water tank. The 
 torch is shown above and between the acid and water tanks. 
 
 The Fumigator. 
 
 Fig. 22. — The Fumigator in the act of charging a generator under the hoop tent. 
 
27 
 
 The tent men are shown in diagram (No. 20) as they are backing off 
 with the end of the rope. They continue to back off as indicated till 
 the tent is over the tree, then proceeding to the tent they adjust the 
 bottom as they pass around it, one on either side. Proceeding to the 
 next tent they attach their poles, then going to the other end of their 
 poles, hold them down with their feet as they pull on their ropes and 
 raise the edge of the tent. As soon as the pole is high enough they 
 back off, and the ends of the lines show the position corresponding 
 with that they had at first. The variations depend on differences in 
 the plan of estimation, and in the kind of tent. 
 
 Estimating the Dose. — The responsibility in the whole process rests 
 on the fumigator, for he is the one who chooses the quantity of the 
 dose; in practice the amount prescribed depends upon his personal 
 judgment. The fumigator looks at a tree and says eight ounces, six and 
 a half ounces or ten ounces according to his idea of its size. The result 
 is that a great deal of unsatisfactory work is done. The wonder is, that 
 the results are as uniform as they are. There are two ways of verify- 
 ing one's judgment as to the proper doses to be given. The one most 
 commonly used is a subsequent inspection of the trees; the practice 
 being to give a little more gas than the trees will stand without injury. 
 If the slight injury produced is the same on all the trees, the fumiga- 
 tor 's judgment is supposed to be working normally. This is very 
 misleading, for the larger the tree the greater the injury, if the dose is 
 properly proportional to the cubic content. The reason for this is the 
 difference in the generation of the gas in large quantities, and its 
 relatively slower diffusion in a large volume. 
 
 The other method is to measure the tree and find the amount of the 
 dose by consulting the tables. If the tables are correctly calculated 
 and the measurement accurately done, this is a safe method, but there 
 are grave difficulties in the way of accurately measuring a tree. If not 
 tented, it is difficult to judge how much to allow for the bending of the 
 branches under the weight of the tent. If tented, which is really the 
 correct way, there are practical difficulties in measuring the diameter 
 and height. To simplify the measurement and estimation of a tent 
 the following table is prepared. The center column gives the various 
 doses corresponding to the sizes of trees given in the columns on either 
 side. Those on one side have been calculated so as to give three parts 
 of hydrocyanic acid gas in 1000 parts of air (or 0.3 per cent.), on the 
 other side two parts in 1000 of air (or 0.2 per cent. ) . For winter treat- 
 ment for deciduous trees 0.3 per cent, gas is suggested, and is nearly 
 the strength recommended in the Eastern states for the San Jose scale. 
 One-half of this amount is not far from the commonest practice in this 
 State for the citrus trees. The 0.2 per cent, gas is suggested for 
 citrus trees and agrees with the amounts used by some of the most 
 successful fumigators, though others get fair results with scarcely 
 more than half this amount. 
 
 The measurements to be taken when using this table are, (1) around 
 the tent, and (2) over the tent from ground to ground. If these two 
 measurements are about equal, as they will be for many orange trees, 
 the number nearest the measurement is found in the circumference 
 column, and the corresponding dose will be seen in the center column. 
 
28 
 
 Table Showing Doses Suitable for Trees of Different Measurements. 
 
 0.3 Per Cent. Gas. 
 
 4 Ounce 
 Differential. 
 
 Circumference 
 of Tree. 
 
 Ft. 
 
 In. 
 
 Ft. 
 
 In. 
 
 3 
 
 5 
 
 19 
 
 1 
 
 3 
 
 
 20 
 
 6 
 
 2 
 
 7 
 
 21 
 
 11 
 
 2 
 
 4 
 
 23 
 
 
 2 
 
 2 
 
 24 
 
 1 
 
 1 
 
 11 
 
 25 
 
 1 
 
 1 
 
 10 
 
 26 
 
 
 1 
 
 9 
 
 26 
 
 10 
 
 1 
 
 8 
 
 27 
 
 8 
 
 1 
 
 7 
 
 28 
 
 5 
 
 1 
 
 6 
 
 29 
 
 1 
 
 1 
 
 5 
 
 29 
 
 9 
 
 1 
 
 4 
 
 30 
 
 4 
 
 1 
 
 3 
 
 31 
 
 6 
 
 1 
 
 2 
 
 32 
 
 7 
 
 1 
 
 1 
 
 33 
 
 8 
 
 1 
 
 
 34 
 
 8 
 
 
 11 
 
 35 
 
 7 
 
 
 10 
 
 36 
 
 6 
 
 
 10 
 
 37 
 
 5 
 
 
 9 
 
 38 
 
 3 
 
 
 9 
 
 39 
 
 
 
 8 
 
 39 
 
 9 
 
 
 8 
 
 40 
 
 5 
 
 
 7 
 
 41 
 
 2 
 
 
 7 
 
 42 
 
 8 
 
 
 7 
 
 43 
 
 11 
 
 
 6 
 
 45 
 
 
 
 6 
 
 46 
 
 1 
 
 
 6 
 
 47 
 
 2 
 
 
 5 
 
 48 
 
 2 
 
 2 
 
 2i 
 
 3 
 
 31 
 
 4 
 
 4i 
 
 5 
 
 5i 
 
 6 
 
 6* 
 
 7 
 
 n 
 
 8 
 
 9 
 
 10 
 11 
 12 
 13 
 14 
 15 
 16 
 17 
 18 
 19 
 20 
 22 
 24 
 26 
 28 
 30 
 32 
 
 0.2 Per Cent. Gas. 
 
 Circumference 
 of Tree. 
 
 Ft. In. 
 
 22 1 
 
 23 7 
 25 
 
 26 
 27 
 
 28 
 
 29 10 
 
 30 9 
 
 31 8 
 
 32 7 
 
 33 4 
 34 
 
 34 8 
 
 36 1 
 
 37 5 
 
 38 7 
 
 39 10 
 
 40 11 
 
 41 11 
 
 42 10 
 
 43 9 
 
 44 8 
 
 45 
 46 
 47 
 48 
 50 
 51 
 52 
 54 
 55 
 
 h Ounce 
 Differential. 
 
 Ft. In. 
 3 11 
 3 4 
 2 11 
 2 8 
 2 6 
 2 4 
 2 2 
 2 
 
 1 10 
 1 9 
 1 8 
 1 
 1 
 1 
 1 
 1 
 1 
 
 1 1 
 1 1 
 
 1 
 11 
 11 
 
 10 
 10 
 10 
 9 
 9 
 8 
 8 
 7 
 7 
 
29 
 
 If these two measurements are not nearly the same, the outside 
 columns become of use, for they show for each size how much differ- 
 ence must occur to make necessary a half ounce increase or decrease 
 in the dose. That is, for each differential there must be added or 
 deducted one-half ounce of cyanide. For instance, if the difference 
 between the distance over and around the tree is 5 feet, and the differ- 
 ential for that circumference is 3 feet 11 inches, then the dose must 
 be increased or diminished by a little more than one-half ounce; but if 
 that differential be 1 foot, then for each foot there must be added or 
 subtracted one-half ounce, or 2^ ounces for the five feet. 
 
 As an example, suppose a tree were 35 feet around and 36 feet 
 over the top, and a person were using the 0.2 per cent, table : Running 
 down the circumference column we find that 34 feet 8 inches (the near- 
 est to 35 inches) requires 8 ounces and that the differential is 1 foot 
 6 inches, that is, 35 feet requires a little over 8 ounces, and the 
 difference between the two measurements around and over the tree, 
 1 foot, is nearly enough to require another half ounce, so that 8 h 
 ounces would be about right. Suppose, again, the distance around 
 a tree to be 40 feet, and that over the top only 35 feet; using the same 
 table, we find opposite 39 feet 10 inches (the nearest to 40 feet) the 
 dose 12 ounces. But the distance over the top is 5 feet less, and a less 
 amount of cyanide will be necessary. We therefore use the differential 
 (1 foot 2 inches) and deduct one-half ounce for each 1 foot 2 inches 
 difference, or about 2 ounces altogether. This leaves 10 ounces as 
 the correct dose for this tree. 
 
 These measurements are not supposed to be taken with every tree, 
 but in cases of doubt, and occasionally to correct one's judgment; and 
 in the case of those beginning to fumigate, whose judgment is not yet 
 developed. 
 
 Estimating the size of the tree is usually done by one of three plans. 
 Some persons plot the orchard in the day time, indicating the dose for 
 each tree, and fumigating at night in accordance with this prearranged 
 plan. They claim, with some show of truth, that they are better 
 acquainted with the trees by daylight and can more accurately estimate 
 their size. Others do this at night, a row at a time, maintaining that, 
 with practice, it can be done with as much accuracy as when done in the 
 day-time, and that the danger of mistaking the rows is lessened. The 
 third plan, which seems the most rapid and accurate, is to make the 
 estimate after the tent is on the tree. The weighing of the cyanide is 
 done at night as a rule, but those working by the third plan generally 
 have it weighed in the day-time. 
 
 When the weighing is to be done at night, a base of supplies is 
 established as near the center of the field as possible, and the cyanide 
 and acid, as well as the water, are dispensed at that point, the gen- 
 erators being carried there on trays. A generator tray is a frame 
 holding four generators in a row, or eight if stacked two deep; a 
 person can carry two trays, or generators enough for sixteen tents. 
 After the chemicals are ready, the "fumigator" takes up his tray of 
 cyanide, and the helper two trays of generators, and they proceed to 
 tent after tent, leaving and charging a generator at each tent. When 
 half-way along the row, the helper drops a tray that has been emptied; 
 when he reaches the other end, both trays are empty. The generators 
 
30 
 
 are arranged on the trays, as are also the doses of cyanide on the 
 fumigator' s tray, in the order of the trees. The next work for the 
 fumigator is to estimate another row of trees, and while he is doing 
 this the helper gathers np the generators of the previous row. They 
 soon both arrive at the base of supplies and proceed to measure and 
 weigh the chemicals for a row on the other side. The details of the 
 third method have already been described. 
 
 When the weighing is done in the day-time, the average dose is 
 commonly weighed into each can or bag, and a little added or subtracted 
 from the dose as the size of the tree may indicate. When the trees 
 are very uniform, the dose thus varying but little, this may do very 
 well; but if the variation is greater, it will be well to have different 
 sized doses weighed out. When this is done the can or bag should 
 indicate clearly the amount of its contents by its different shape or 
 character. This method seems distinctly preferable to night weighing. 
 
 Charging. — The generator now universally used is the ordinary 
 earthenware vessel or chamber, the cheap yellow ware being generally 
 selected. Some use a perforated sheet-lead cover, but generally no 
 cover is used. The fumigator places the generator on the ground 
 near the trunk of the tree and is then ready to charge it, which he 
 accomplishes by dropping the cyanide into the diluted acid in the gen- 
 erator. He has the cyanide either in tin cans or in small paper bags; 
 in the former case he pours the cyanide into the acid, keeping the can, 
 which he replaces in his tray, but in the latter case breaks the bag 
 and drops it into the acid, bag and all. Some fumi gators prefer to 
 add the acid last, in which case the helper brings the generator with 
 only water in it, and keeps the acid in a small pitcher, one for each 
 generator. In this case the fumigator puts the cyanide in the gener- 
 ator, as before, and then pours in the acid. 
 
 Poisonous Nature of the Gas. — All the work of the fumigator under 
 the tent is done at arm's length. There is no poison more dangerous 
 or fatal than hydrocyanic acid. The danger from the gas is greatest as 
 it is coming up from the generator. This is so well understood that 
 though the gas has been used for years by a great many people, we 
 have never heard of an accident with it. There seems to be no injur- 
 ious effect from breathing the diluted gas that fills the air when the 
 tents are removed, even though it may smell very strong and one can 
 feel it very plainly in his throat and chest. Working every night, for 
 months at a time, does not develop any abnormal symptoms, so it can 
 be safely said that, with proper care, there is no particular danger in 
 the use of the gas. 
 
 Inspection. — Wherever fumigation is carefully done the tents will 
 be thoroughly inspected every day. To do this the inspector goes 
 beneath the tent as it lies on the ground, and any holes will be at once 
 seen by the light streaming through; these places are marked and 
 patches applied. Sometimes the patch is glued on, but the usual and 
 preferable way is to sew it on. Sewing is done by hand in the same 
 way as sails are mended, or sometimes a sewing machine is used. 
 
31 
 Concluding Remarks. 
 
 The uniform testimony of those that have used fumigation exten- 
 sively is that by no other means at any cost can as effective work be 
 done as by proper fumigation. It is also true that at no place where 
 fumigation has been followed for years is it believed that the method 
 is eradicative. Some, indeed, think that it would be if universally used, 
 but those longest acquainted with the process do not claim that for 
 it. When it is well done, the insects that escape are far below one per 
 cent; but with insects capable of increasing several hundred per cent, 
 in a single season, the destruction of over ninety-nine per cent, is 
 certainly not a bad result. 
 
 The question between fumigation and spraying will usually resolve 
 itself into this : If the interest of the tree or crop demands a degree of 
 freedom from scale insects that cannot be insured by one or two 
 sprayings, fumigation will be resorted to. The cost of cyanide has 
 been reduced about one-half since fumigation was begun, and if it 
 should be reduced to about one-half of what it is now, fumigation would 
 probably entirely take the place of spraying for scale insects on all 
 trees, as it has now done to such an extent in the case of citrus trees 
 that are so difficult to spray. 
 
 List of the More Important Articles on Orchard Fumigation. 
 
 1887 
 Morse, F. W. : The use of gases against scale insects. Bulletin 
 71, University of California, Agricultural Experiment Station, June 12. 
 
 Gives results of experiments with hydrocyanic acid gas as well as with seven 
 other gases. A tent of oiled bed-ticking was used, and the gases were produced in 
 a sheet iron generator and blown into the tent by means of a pump. Numerous 
 gases were used with the hydrocyanic acid to lessen the injurious effects, the 
 most satisfactory being carbonic acid gas. Tables and full directions are given 
 for use on trees of various sizes. 
 
 Morse, F. W. : The use of hydrocyanic acid against scale insects. 
 Bulletin 73, University of California, Agricultural Experiment Station, 
 August 27. 
 
 Contains a fuller description of the apparatus and method generally, and the 
 results of later experiments confirmatory of those previously arrived at. Most of 
 the work of these later experiments was upon minor matters of detail. 
 
 1888 
 Coquillett, D. W.: Report on the gas treatment for scale insects. 
 Report of the United States Department of Agriculture for 1887, pp. 
 123-142, PL 4-6. 
 
 This article gives an elaborate account of the methods of fumigation, and of the 
 experiments of the author with a large variety of gases, the most satisfactory of 
 which was hydrocyanic acid gas. He discusses the patent obtained by Hatch in 
 1867, the experiments of Dimmock in 1877, his own work in 1886-87 and that of 
 Morse in the latter year. The McMullen tent is described, and the Wolfskill, 
 Titus, and Culver fumigators are described and figured. Full directions are given 
 for the generation of the gas by the two methods devised by himself, and for the 
 soda method originated by Morse, including tables giving amounts of chemicals to 
 be used on trees of different sizes. He also discusses the methods of agitating the 
 air in the tent. 
 
32 
 
 Coquillett, D. W. : Supplementary report on the gas treatment for 
 scale insects. Insect life, vol I, pp. 41-42. 
 
 Gives the results of analyses of certain brands of cyanide, and certain details in 
 the generation of the gas. 
 
 Klee, W. G. : Report of the State Inspector of Fruit Pests. Third 
 Biennial Report of the State Board of Horticulture, pp. 242-258, PL 
 
 1-8. 
 
 Makes extracts from Bulletin 73 and from United States Report for 1887, and 
 figures the Wolfskill, Titus, and Culver fumigators, and the Morse generator. 
 
 Morse, F. W.: Experiments on the cause and avoidance of injury 
 to foliage in the hydrocyanic gas treatment of trees. Bulletin 79, 
 University of California Experiment Station, May 5. 
 
 An account of a series of laboratory experiments which led the author towards 
 the view that the development of ammonia was the chief cause of injury to foliage. 
 He was inclined to favor the second method devised by Coquillett as the best for 
 producing the gas. 
 
 1889 
 
 Coquillett, D. W.: Report on various methods for destroying 
 scale- insects. Report of the United States Department of Agriculture 
 for 1888, pp. 123-133. 
 
 In the part devoted to the hydrocyanic acid gas he speaks of some minor 
 details in the construction of the generator. The Leefeld fumigator is described, 
 and a new table given of the amount of chemicals to use. 
 
 Coquillett, D. W. : Hydrocyanic acid treatment for scale insects. 
 Insect Life, vol. I, pp. 286. 
 
 Gives experiments with the gas for red scale, its effectiveness and cost. Also 
 the effects of fumigation on lady-birds and other insects. 
 
 1890 
 
 Coquillett, D. W.: The use of hydrocyanic gas for the destruction 
 of the red scale. Insect Life, vol. II, pp. 202-207. 
 
 Full details of his experiments against the red scale, and of the simplified gen- 
 erator and new formula. A new table of amounts used for trees of different sizes 
 is given with general directions. He prefers a black tent. 
 
 Lelong, B. M. : Improved fumigating apparatus. Report of the 
 State Board of Horticulture for 1890, pp. 469-472. 
 
 Chiefly abstracts from Insect Life, vol. II, but contains working drawings of a 
 form of the Preble apparatus. 
 
 1891 
 
 Craw, Alexander: Destructive insects, their natural enemies, rem- 
 edies and recommendations, 51 pp., Sacramento, 1891. 
 
 On pages 33-36 the author presents brief but comprehensive directions for 
 fumigating, and gives figures of the Preble apparatus. 
 
 1894 
 
 Craw, Alexander: Gas treatment for destroying scale insects upon 
 citrus trees. Report of the State Board of Horticulture for 1893-4, 
 pp. 105-109, PI. 37-38. 
 
 Refers to the poisonous nature of the gas, and gives directions for its genera- 
 tion. Presents two tables of amounts to use on trees of various sizes. And 
 describes and figures hoop and sheet tents, and gives formulas for treating the 
 cloth of the tents. 
 
33 
 
 1898 
 
 Johnson, W. G. : Report of the San Jose scale in Marjdand, and 
 remedies for its suppression and control. Bulletin 57 of the Mary- 
 land Experiment Station, 
 
 Pages 72-95 are devoted to hydrocyanic acid gas, treating upon the early 
 history, the use in greenhouses, and presenting an account of the experiments in 
 Maryland. Very complete directions and reports of the experiments are given and 
 the whole is well illustrated. 
 
 RESUME. 
 Hydrocyanic Acid is the most effective insecticide known, (p. 3.) 
 
 Its value was first made known by a publication from this Station. 
 
 (p. 4.) 
 
 Injury to foliage can be prevented in a number of ways. (p. 4.) 
 
 Night work has proven to be a most important item. (p. 6.) 
 
 The tent and other apparatus has gone through an interesting course of 
 development, (p. 7.) 
 
 The dose of cyanide recommended, has varied considerably, but the 
 original prescription is about right, (p. 7.) 
 
 The tent as now made is of light duck, oiled, sized, and painted, or 
 treated with cactus juice to make it gas tight, (p. 11.) 
 
 Bell tents operated in pairs by means of derricks are much used for the 
 largest trees, (p. 12.) 
 
 Hoop tents are most used and can be moved from tree to tree with great 
 facility, (p. 14.) 
 
 Box tents are a recent Eastern device having some good points and should 
 be tried here. (p. 19.) 
 
 Sheet tents are held in great favor and may replace all other kinds, 
 (p. 21.) 
 
 Fumigating according to a well- arranged plan makes the labor a small 
 item in the cost. (p. 24.) 
 
 Accurate estimation of the area of the tent is essential to successful 
 fumigation, (p. 27.) 
 
 The danger from poisoning is chiefly when charging the generator, (p. 30. ) 
 
 The tents must be inspected daily and kept gas tight, (p. 30.) 
 
 Fumigation may finally entirely replace spraying for scale insects, (p. 31 . ) 
 
LIST OF STATION PUBLICATIONS AVAILABLE FOR DISTRIBUTION. 
 
 The edition of the Report for 1895-97 is exhausted. The supply of all other 
 Bulletins and Reports were destroyed with the Agricultural Building, which was 
 burned in April, 1897. 
 
 Report of Viticultural Work of the Station; 1887-93. 
 
 Resistant Vines; selection, adaptations, and grafting. 
 
 Bulletin No. 116: The California Vine-Hopper. 
 
 Bulletin No. 117 : The Control of Temperature in Wine Fermentation. 
 
 Bulletin No. 119: Vine Pruning. 
 
 Report on Grasses and Forage Plants: Reprint from the Annual 
 Report. 
 
 Bulletin No. 120: The Olive Knot, 
 
 Bulletin No. 121: The Conservation of Soil Moisture, and Economy 
 in the Use of Irrigation Water. 
 
 Circular: The Extermination of Weeds. 
 
 Seed Bulletin for 1898-99: Distribution of seeds and plants. 
 
 The Reports and Bulletins of the Station are sent free to all persons in the 
 State who apply for them.