UNIVERSITY OF CALIFORNIA. AGRICULTURAL EXPERIMENT STATION. BULLETIN NO. 71. The Use of Gases Against Scale Insects, the bottom of the tent and run through a lL Z " , _ at tne upper corners of the scaffold. T as insecticides— with special reference to the j scaffolding, one tent being left over the tree white scale, Icerya Purchasi. The following is while the scaffolding is moved to the next a summary of results, of which a full report! In adjusting the tent, the bottomiis placed on will be published hereafter. the ground about three feet from the tree and The use of gases for this purpose has been covered with earth. This brings the gas to long contemplated, and various appliances have bear upon the base of the tree and the surround- been suggested for the ready application of any ing soil. efficacious gas. The ease with which gas pene- The generator in which the gases were pro- trates to all parts of the tree naturally suggests duced consists of a,heavy sheet-iron cylinder, 11 its use as preferable to washes, which at best inches in diameter and 13 inches high. Thebot leave many parts of the foliage and infested torn rests on a plank, and to the top is fitted a branches untouched, even when sprayed with movable cover suspended in a frame by a the greatest care. In order that the gas may bench-screw. Into the cover are fitted two be an efficient insecticide, it must be so poison- pieces of gas-pipe — one for the exit of the gas ous that even when applied in small quantities toward the tent, and the other, connected with it produces fatal results; for in the application a pump, carries the gas which returns from the the air confined in the tent covering the tree tent. Two small reservoirs are also inserted in dilutes the gas to a great extent. Again, the the cover; in these are contained the solutions gas must be capable of being generated quickly which are to flow into the generator for the in sufficient volume. The record below shows production of the gas. that only one of the gases employed fulfilled In order to establish circulation and to force these conditions to a satisfactory extent. Pre- the gas into the tent, a pump is used, which liminary experiments with some others hav- also serves to exhaust the gas from the upper ing shown their unfitness for the purpose, part of the tent and to force it again through either on account of expense or because of in- the generator. It is proposed to replace the jury to the foliage, or imperfect action on the pump by a small fan-blower, which is much in8ec ts, their study was not pursued further. more expeditious than the common pump which Appliances for Application. wa8 U8e <** TJie tent for covering the tree is made of The Ga898 Experimented With. heavy bed-ticking, thoroughly oiled with linseed Among the gases used were chlorine, sul- oil. This cloth serves the purpose best, as it is phuretted hydrogen, ammonia, carbon bisul- very closely woven, is pliable and easily phide, carbon monoxide, carbonic acid, hydro- folded, cyanic acid, and carbolic acid vaporized by The support of the tent, devised by Mr. heat. Titus, is a very ingeniously contrived scaffold- Chlorine. — Some preliminary experiments ing mounted on wheels, which serve to move it were made in small vessels into which this gas from one tree to another. Its dimensions had been introduced. Some infested branches are 26 feet high, with a base 20x20 feet, were allowed to remain in them for times vary- Its upper part is 20x12, and carries upon ing from 5 to 35 minutes, without any notice the top a roller made of galvanized iron (6 able effect being produced on the insect. At- taches in diameter and 12 feet long), upon mospheres more strongly saturated with the which the tent is rolled when taken from gas proved fatal to the insect in a short time, the tree. Side guy-ropes are attached to In other treatments extending over 18 hours, with leas saturated atmospheres, only a smal percentage of the insects was killed. No decided| effects were noticeable on the foliage unless the) gas was very concentrated. Carbon Bisulphide.— A lime tree, 12 feet inj diameter of top, was treated with the vapor of! 2£ pounds of sulphide of carbon for 45 minutes.! At the end of this time the insects were lively, and during the treatment had crawled up and collected around a rope surrounding thar tree, at the point where the gas was being injected from the hose. It proved that the gas thus used injures neither the insects nor the foliage. It is upon record, however, that in cases where the vapor has not been thoroughly diffused, but was allowed to flow down from an open vessel placed in the top of the tent, serious injury was done to the foliage at points where the undiluted vapor flowed down. Sulphuretted Hydrogen.— Several treatments with this gas were made on a small scale, the application lasting from 5 to 35 minutes. The effects produced either with diluted or concen- trated gas were similar to those produced by ohlorine, except that even the concentrated sul- phuretted hydrogen did not injuriously affect the foliage. An experiment in which a whole tree was treated in the tent for 45 minutes, with quite concentrated sulphuretted hydrogen gas, showed clearly that the effect was far from be- ing satisfactory; the insects for the moment were stupefied, but in the course of an hour and a half the majority of them were again moving about. Ammonia. — The vapor from one pound and a half of strong ammonia water was applied to an 11 -foot lime tree for 30 minutes. The re- sults were disastrous to the foliage; the leaves were all scalded, and in a few days all dropped from the tree, and even the newer growth of wood was injured. The insects, however, were not perceptibly harmed. Carbon Monoxide. — Very strong hopes have been entertained by many for the successful ap- plication of this gas. Its apparent cheapness and easy production, when the necessary plant is once erected, would recommend it. Unfor- tunately our experiments show that it is not sufficiently effective to warrant its use. The gas was obtained by forcing air through a small furnace filled with red-hot charcoal, care being taken to cool and to measure the gas before ap- plying it. No appreciable effect was noticeable after 40 minutes. In a duplicate experiment, in which the charcoal was more strongly ignited and continuously introduced into the barrel for 30 minutes, only slightly better results were ob- tained. Oxalic Acid. — It was thought that the pro- duction of carbon monoxide by decomposition of oxalic acid by heat might be substituted for the previous method of generating this gas. One-quarter of a pound of oxalic acid was ignited, and the gases applied in a manner sim- ilar to that of the preceding experiment. Neither the insects nor the foliage were harmed in the least. This experiment has incidentally shown that the vapor of formic and oxalic acids, also produced during the heating of the latter is likewise ineffective. Carbolic Acid. — It had been suggested that carbolic acid vaporized by heat would prove fatal to the insect. A dose of half a pound of liquid acid was volatilized in the furnace, and the vapor blown in the vessel containing the infected branch. At the end of 20 minutes all the old insects were still alive, and some of the young ones, just molted, were moving about. An hour later the foliage appeared as if scalded. Hydrocyanic Acid.— -It was only with hydro- I cyanic, or prussic acid (generated by the action i of sulphuric acid on potassium cyanide), that sufficiently fatal effects were secured to war- rant a more thorough determination of the time of exposure and quantities of material which would produce the best resultB. Numerous ex- periments were carried on for this purpose, and it was shown that even small amounts were ef- fective. It was also shown that even in these 8m all quantities an injurious effect upon the foliage was produced. In the beginning of the experiments, 11 mining cyanide" of potassium was used. It is a very impure material and contains along with the cyanide a considerable amount of carbonate of potassium. For this reason many of the first treatments were prac- tically ineffective. Later treatments with pure cyanide were more successful in destroying the insects, but the foliage was proportionally injured. Treat- ments varying in dose from 4 to 12 ounces of cyanide, and in time from 15 to 60 minutes, showed that the effect produced on the foliage by longer treatment was not proportionally greater than that produced by short treatment. Neither was the effect of longer treatments proportionally more fatal to the insects. It was thus clearly shown that the gas mixture should be of considerable strength in order to insure rapid action. The effect of the gas was so disastrous to the foliage that it became necessary to find some means of remedying this trouble. This was sought in applying a second gas, which might preserve the foliage. Sulphuretted hydrogen was therefore injected into the tent, together with the cyanide gas, both from the same gen- erator; a portion of the sulphuretted hydro- gen being introduced before the cyanide was generated. It was found that the insects ap- peared stupefied when the tent was raised, but large numbers revived in a few hours. The effect of the cyanide seemed therefore to have been decreased by the sulphuretted hydrogen. The foliage was not preserved, although not so badly affected as by treatments with cyanide alone. Carbonic acid gas was next tried. Trees were treated with larger doses of cyanide than heretofore used, and the carbonic acid from 1£ pounds of carbonate of soda was at the same time introduced with these doses. The insects were killed and the foliage of a 12-ft. tree remain- ed unharmed, while that of a 14-ft. tree with the the same amount of carbonio acid was slightly injured. Thus it was shown that it would re- quire 1£ pounds of bicarbonate of soda to pre- serve tree-tops 12 feet in diameter, and that with this protection the deadly cyanide could be successfully used. The regulation of the doses for the different sized trees so as to produce uniform treatments is calculated on the basis of the results of thej liage is protected by the carbonic acid gas. experiments which determined the amount of each constituent for a 12-foot tree. The fol lowing table indicates the amounts for trees of different dimensions of top, based upon the rates of cubical contents: oize 01 Tree, feet. Cyanide of Potassium, fluid ozs. tSi-Carbonate of Soda, pounds. bulpnunc Acid, fluid ozs. 4 •7 •05 •4 5 1.6 .11 •3 6 2-5 .20 M 7 4.0 .29 2.1 8 6.o .44 3.1 9 8-5 .63 4-5 IO "•5 .87 6.2 ii 15-5 1.14 8.2 12 20.0 1.50 11,6 13 25-4 1.90 13-5 14 31.6 2.50 16.6 15 39-2 2 92 20.7 16 47-5 3-55 25.2 17 57-5 4-23 30.1 18 67.7 5.o5 35-8 19 70.9 5-93 42.1 20 90-5 6.93 49.2 In order to apply the doses easily they are prepared so that the required amounts of each ingredient can be directly measured. The cyan- ide solution is prepared by dissolving say 10 pounds of the solid salt in about 2£ gallons of water, warmed nearly to the boiling point, stir- ring at intervals, cooling, and then diluting to 2J gallons. This solution will contain about one It is advisable that the treatments should follow cultivation after about four days, so that all weeds and places where the insect may find lodgment would be destroyed. The insect will then be on, or very near, the tree; the fitting of the tent to the ground is thus also much easier. The eggs of the insect remained apparently uninjured, wherever protected by the woolly covering. A second treatment, to destroy such as may afterward hatch, will therefore be nec- essary. It must not be understood that these experi- ments definitely settle the mode of operation and the Bize of the doses to be used. They are merely suggestive of a general plan which can be so perfected in the future that the applica- tion of this remedy to other kinds of trees and insects must be attended with good results. It simply remains for the ingenious cultivator to devise the necessary appliances for its use, on a small scale, on all sorts of fruit trees, shrubs and plants. It must not be forgotten that extreme care in the handling both of this deadly gas and of the cyanide itself is necessary. To inhale the one, or to taste or touch a wound with the other, may lead to serious consequences. Berkeley, June 12, F. W. Morse. Aotion of the Los Angeles Supervisors. Just after the foregoing was written, the fol- lowing letter was received from A. Scott Chap- ounce of cyanide of potassium to 2J fluid ouncea ™ an .> ° f Sa ° G /{l rie !'. m f. mber of the California of the liquid. State Board of Horticulture: The bicarbonate of soda is pulverized finely rr %M San Gacriel, June 8, 1887. and measured off in a vessel marked, so as to e F > -Morse, University of Cah/ornia-DEAR designate pounds and fractions of a pound of SlR: ™e Board of Horticulture of Los Angeles , , 6 ,. , r . . , T . . , i • au county nave been out to examine the work done by the solid material. It is then placed in the gen- J Ml , Titus> lace and bave pronounced it th £ erator and the dose of cyanide mixed best .. killing - that they have ever seen> with it, and, if necessary, a little water added They asked my father (Mr. A. B. Chapman) to go to make it into a thin paste. ^ After before the Board of Supervisors and make a state- adding the measured dose of sulphuric acid, ment of your work. He went before the board and the pump is worked slowly at first, and more explained things to tnem. .They then agreed to pay rapidly after the gas has passed into the tent, all the expenses incurred by him and Mr. Titus; The time for each treatment must be deter- the y further agreed to ask you to come down again mined by future experiments; 15 minutes a J? d carr y y° ur P Ian *° completion, agreeing to pay seemed to be quite sufficient when the cyanide a11 your expenses and salary, the same as was done i i 1 t. si u a • ui 1 by Mr. Titus and my father, during your previous alone was used but it may be desirable to ex- ^ " v ^spectrally yours, tend the treatment to 30 minutes when the fo- A. Scott Chapman.