UNIVERSITY OF CALIFORNIA PUBLICATIONS. COLLEGE OF AGRICULTURE. AGRICULTURAL EXPERIMENT STATION. FUMIGATION DOSAGE. By C. W. WOODWORTH. The Fumigator in the Act of Charging a Generator Under the Hoop Tent. BULLETIN No. 152 (Berkeley, June, 1903,) SACRAMENTO: w. w. shannon, : : : : SUPERINTENDENT state printing. 1903. BENJAMIN IDE WHEELER, Ph.D., LL.D., President of the University. EXPERIMENT STATION STAFF. E. W. HILGARD, Ph.D., LL.D., Director and Chemist. E. J. WICKSON, M.A., Horticulturist, and Superintendent of Central Station Grounds. W. A. SETCHELL, Ph.D., Botanist. ELWOOD MEAD, M.S., C.E., Irrigation Engineer. R. H. LOUGHRIDGE, Ph.D., Agricultural Geologist and Soil Physicist. (Soils and Alkali.) C. W. WOODWORTH, M.S., Entomologist. M. E. JAFFA, M.S., Assistant Chemist. (Foods, Fertilizers.) G. W. SHAW, M.A., Ph.D.. Assistant Chemist. (Soils, Beet-Sugar.) GEORGE E. COLBY, M.S., Assistant Chemist. (Fruits, Waters, Insecticides.) RALPH E. SMITH, B.S., Plant Pathologist. A. R. WARD, B.S.A., D.V.M., Veterinarian, Bacteriologist. E. H. TWIGHT, B.Sc, Diploma E. A.M., Viticulturist. E. W. MAJOR, B.Agr., Dairy Husbandry. A. V. STUBENRAUCH, M.S., Assistant Horticulturist and Superintendent of Substations. WARREN T. CLARKE, B.S., Assistant Field Entomologist. H. J. QUAYLE, B.S., Assistant Entomologist. H. M. HALL, M.S., Assistant Botanist. GEORGE ROBERTS, M.S., Assistant Chemist in Charge Fertilizer Control. C. A. TRIEBEL, Ph.G., Student Assistant in Agricultural Laboratory. C. A. COLMORE, B.S., Clerk to the Director. EMIL KELLNER, Foreman of Central Station Grounds. JOHN TUOHY, Patron, ) y Tulare Substation, Tulare. JULIUS FORRER, Foreman, ) R. C. RUST, Patron, > >• Foothill Substation, Jackson. JOHN H. BARBER, Foreman, ) S. D. MERK, Patron, ) „ _ , . , > Coast Range Substation, Paso Robles. J. H. OOLEY, Workman in charge, ) -on, ) Y Southern California Substation, < J. W. MILLS, Foreman, ) { Ontario. S. N. ANDROU3, Patron, ) (Pomona. J. W. MILLS, Foreman, j V. C. RICHARDS, Patron, T. L. BOHLENDER, ROY JONES, Patron, WM. SHUTT, Forema Forestry Station, Chico T. L. BOHLENDER, m charge ' 1 t Forestry Station, Santa Monica. The Station publications (Reports and Bulletins) will be sent to any citizen of the State on application^ so long as available. FUMIGATION DOSAGE. Practical fumigators in California have been notoriously at variance with each other in their estimation of the dose of cyanide required for a tent of any given size. They all uniformly claim that they endeavor to place under each tent all that can be used with safety to the tree. Those using the larger dosage often claim that the others are not using enough, and these, on the other hand, usually maintain that under their local conditions a larger dosage is impossible without injury. The common method employed by fumigators to verify the correctness of their estimates is to examine the orchards the day after fumigation, and they are satisfied if here and there slight traces of injury to foliage can be seen. It was supposed by us that these differences of practice among fumi- gators were really justified by the facts, and the present investigation was undertaken to determine and record the best practice of the various regions. One would naturally expect that after all these years there would have come to be certain recognizable standards based upon practical experience. For the purpose of determining the actual practice, Mr. J. S. Hunter was sent into the field and spent nearly two months visiting practically every fumigation outfit operating in the State, making measurements of the tented trees and recording the doses assigned to them. In this way we have secured dosage and measurements of 2,314 trees, representing the judgment of thirty fumigators. The data thus obtained have failed to indicate that the practical experience has resulted in a satisfactory solution of the problems of dosage. We have found, as will be shown below, that the judgment of all the fumigators is thoroughly unreliable. It is doubtless a physical impossibility to guess with any degree of accuracy the capacity of a tent. The remarkable thing is that the results obtained in fumigation in the killing of scale insects have been uniform enough to be fairly satis- factory. They show that the process of fumigation allows a very wide margin between efficiency against the insect and danger to the plant. A reformation in the method of estimating the dose could not fail either to greatly diminish the cost of the chemicals used, or to improve markedly the certainty and uniformity of the results. 4 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. THE METHOD OF MEASUREMENT. The method used in making the measurements of the tents in this study was quite simple, and consisted in the use of a fishing-rod and wire line. A piece of electric drop-light insulated cord was used as the line. This consists of a cable of many fine copper wires covered with thread, which gives greater flexibility and is less liable to kink than a simple wire. The line was marked off' into one-meter lengths by knots. The metric system was used because of convenience in calculation. The rod employed was the ordinary jointed fishing-rod, which could be disconnected for transportation and adjusted to different heights of Fig. 1. The method of measuring tents employed in securing the data discussed in this bulletin. trees. The sections of the rod were marked off into centimeters for use in connection with the line in making the measurements. The procedure in making the measure of a tent is as follows: Having first attached the line at about its middle to the end of the rod, one end of the former is made fast to the tent. The most convenient way to accomplish this was found to be by means of a hook, like a fish-hook from which the barb had been removed. The most convenient place of attachment was at a point one meter from the ground. After attaching one end of the line to the tent the rest of that half is caused to lie up to and over the center and top of the tent by means of the rod. The one making the measurement then walks around to the opposite side of the tent, rod in hand, holding the line constantly in position over the top. The other end of the line is carried around FUMIGATION DOSAGE. O the tent at the same time and is then drawn taut, measuring the last fraction of a meter by means of the graduation on the lower joint of the rod. Adding now one meter, the distance the first end is from the ground, we have the measurement of the distance over the top of the tent from the ground on one side to the ground on the other. A second measurement was then taken by throwing the line off the top of the tent by means of the rod and holding it so that as the meas- urer proceeds around the tent to the point where the line is attached, it will encircle the tent at a point about one meter from the ground. The end of the rod is again brought into requisition and the last fraction of meter read in centimeters. Both measurements are thus made by one person in a single trip around the tent. Mr. Hunter found that he was able, after a little practice, to measure as rapidly as the tents could be shifted. This we believe is much more rapid than is possible by any other method that has ever been used for this purpose. It may, however, be more accurate than would be needed in actual fumigation practice, and the method suggested below is therefore more available. Some method of measure- ment, however, should by all means be adopted. CALCULATION OF VOLUME. The shapes of trees differ very greatly, and are, indeed, always more or less irregular. The exact calculation of the volume of a tent is a very difficult matter and is really never attempted. Two dimensions are measured and the tent calculated as a regular figure. The regular figure that comes nearest to the shape of a tented tree is that of a cylinder surmounted by a hemisphere. The mathematical formulas for the volume of a tent of this shape are: ^(A-0and£(o-^) In the first formula, h is the height and r one half the diameter. These are the dimensions usually given by writers on fumigation, but are not the measurements most easily made. The writer suggested, in Bulletin No. 122 of this Station, the two measurements that were employed in getting the data upon which this study is based. These measurements are indicated by c, circumference, and o, the distance over the top of the tent, in the second formula above. The actual capacity of tents of various dimensions was determined by using the diagram, Fig. 2, the curves giving the volume in steres — that is, in cubic meters. A stere is approximately 35^ cubic feet. By the use of this diagram one may readily determine the volume of a tent if he have the dimensions according to either method of measuring, and in either the common or the metric system. The two oblique lines 6 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. represent the range actually found- in the shape of the trees being fumi- gated. The curved lines show the various volumes in the cube of the Distance over top of Tent Fig. 2. Diagram for calculating volume of fumigation tents. unit of measurement. Thus, a measurement made in yards would give the volume of a tent in cubic yards. FUMIGATION DOSAGE. 7 The theoretical shape of tent for which all these calculations are made represents the largest possible volumes for the given dimensions. Any variation, therefore, due to the irregularity of the tree decreases the actual volume of the tent. This is on the safe side, since the all- important thing in fumigation is to have the dose strong enough to insure the death of the insects. LOCAL VARIATION. The difference in the practice of different fumigators is very evident upon the most cursory examination of the data obtained, but the com- parison of the data in a way that will eliminate other causes of variation than the one under immediate consideration is far from easy. In order to ascertain if there is any variation distinctly associated with localities, comparisons were made between the recorded dosage of the same sized tents as estimated by the various fumigators. The trees varied so in height in the different orchards that in some cases most of the treated trees were below this size and in other cases above, indeed quite a number had to be left out altogether in this comparison. The dimension chosen for the comparison of localities was ten steres, and in the table that follows all measurements indicating the size between nine and eleven steres are included: Ounces Used. Number Locality. of Trees. Ventura County — Filmore 12 Los Angeles County- Pasadena _ _. 19 Sunny Slope.. _ 1 Arcadia 9 Duarte _ 11 Covina (1) 2 Covina(3).._ 11 Covina(4) ._ 2 Covina(5) 1 Glendora _ _ _ 3 Pomona 1 San Bernardino County- Ontario (1) 6 Ontario (2) 6 Ontario (3) 2 Ontario (4) 2 Orange County— Placentia 6 Anaheim _. 2 Santa Ana 14 Orange (1) _ 1 Orange (2) 12 Tustin 2 San Diego County — Escondido . 2 National City _. 9 Range. Minimum. Maximum. DO 2 3 2K 3^ 2.9] 2M 2K 2.5 3K 5 3.9 4K 5 4.8 4 4 4.0 3 4 3.5 4 4K 4.3 2K 2M 2.5 4 5 4.7 3 3 3.0 J 3 4 3.51 3 4 3.3 ! 3 3 3.0 ( 3 3 3.0 J 4 4K 4,7 1 4 4 4.0 3 6 4.8 7K 7K 7.5 3 6 4.8 3 4 3.5 J 1 1 1.0 J 2K 3y 2 3.0 f Average Dose. 2.4 3.6 3.2 4.8 2.0 8 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. Riverside County is omitted from the above table, since we have no estimates of dosage for trees as small as those included in the table. The arrangement of the table by counties is quite natural, as will be seen by the accompanying map. (Fig. 3.) The small dosage in Ventura and San Diego counties may account in part for the disfavor in which the process is held by many orchardists of those districts. It is at least interesting to note that in the counties where the process is least known the dosage is the smallest. The largest dosage is in the county where the orchardists to the largest extent manipulate their own tents, or rather have done so in the past. Most of the work here as elsewhere is now done by contract. The greatest uniformity is in San Bernardino County, where the county inspection appears to have borne fruit in a way that should SAN BERNARDINO CO MAP SHOWING LOCATION .Escondido ORCHARD FUMIGATION WORK \ ^ Q CO CALIFORNIA ^tic^i city Fig. 3. gratify the orchardists of that county. As a contrast to this stands Los- Angeles County. The parts of these counties in which fumigation is practiced lie immediately adjacent to each other, and the average dosage is about the same. The average is slightly higher than in the former county, but some fumigators run very low and others very high in their estimates. Here the work is often of the most satisfactory sort, and at other times but little good seems to be done. The measurements suggest a very possible explanation of the irregularity of the results obtained. A very exhaustive study of the killing dose of cyanide gas should be provided for the coming fumigation season, and the desirability of a very close inspection of fumigation operations is also evident. PERSONAL VARIATION. While fumigators of a locality may come to have some degree of agreement in the average size of the dose employed, each one exhibits a great deal of irregularity in his judgment of the size of the trees. One very prolific source of error in this respect is the practice, that has* now FUMIGATION DOSAGE. 9 become almost universal, of estimating the dose before the tent is on the tree. According to the arrangement of the branches, trees will respond very differently to the pressure of the weight of the tent. The diagrams (Figs. 4 and 5) illustrate the method of plotting the dosage of trees as used in the study of the data accumulated for this investigation. Fig. 4 shows the estimates of ***** forty-eight trees made by one of the fumigators at «i Ontario, and is about as "** uniform as any we have found. The oblique lines indicate the size of the tree, and the numbers the dose. It will be seen that the same sized tree was judged to require in one case a dose of 3 Fig. 4. Dosage of fumigation tents plotted on curves showing ounces and in others 3^ and 4. Likewise practi- cally the same sized tents might be supposed to require 4, 4-J, or 5 ounces; or again, we find 4-§, 5, 5-§, and 6^ ounces all for about the same sized tent. It is usual to find much worse cases than this, as is shown in Fig. 5. The success of any method of treatment depends in a large measure on the proper strength of the insecticide used. Fumigation particularly Fig. 5. Dosage of two fumigators plotted as above. requires this, because an under dose does not kill at all. It would appear that two changes must be made to insure uniformity in dosage: first, estimation after tenting, and, second, estimation from actual measurements. 10 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. SMALL VS. LARGE TREES. All the tables of dosage that have so far appeared for the guidance of fumigators have intended to give the volume of the tents in terms of ounces. Some have by faulty calculation increased the dose of smaller trees and decreased that of the larger ones. In actual practice this modification of the two ends of the table is regularly followed. No one has attempted to determine how much the practice of dosage varied from the calculated volume of the tent, but every one who has attempted to measure at all knows that such variation exists. In the following table we have attempted to tabulate the results of our measurements so that they will express it as accurately as possible: Approximate Dosage. Locality. ^/s. % Twice. % Average. % Half. % Quarter. % Eighth. £™ T&8 \ Orange (1) 9 72 §y 2 69 \y 2 30 70 Escondido (2) .... 6^ 62 4 63 2% 30 62 Covina (4) 6 91 b% 82 4% 86 3 25 86 Covina (5). 7 86 6 91 by 2 55 3 67 2 22 75 Tustin 7 86 6 83 5 50 2y 2 80 2 75 \y 2 20 74 Pomona... S l A 86 3 20 86 Placentia.... 6 91 by 2 15 91 Glendora 9 67 6 67 4 50 2 15 61 Ontario (4) 5 80 4 75 3 83 2y 2 15 79 Ontario (2) 4 75 3 15 75 Ontario (1) 6 67 4 75 3 15 71 National City .... 5^ 64 3^ 71 2^ 80 2 15 72 Pasadena...'. 4 88 3^ 68 2 15 75 Filmore Zy 2 86 3 83 2y 2 80 2 15 83 Arcadia iy 2 67 5 80 4 63 2y 2 14 70 Escondido 3 50 \y 2 67 1 12 58 Covina (6) 8 75 6 67 4 75 3 83 2y 2 80 2 10 76 Santa Ana 6 67 4 75 3 83 2y 2 80 2 10 76 Ontario (3) 5 60 3 83 2y 2 10 71 Anaheim 6 83 5 80 4 75 3 83 2y 2 80 2 10 78 Orange (2) 6 42 \y 2 77 3^ 71 2y 2 80 2 9 64 Duarte ... 5y 2 82 \y 2 77 ?»y 2 71 2y 2 7 77 Sunny Slope V/ 2 71 2y 2 80 2 6 75 Covina (1) 3^ 71 2y 2 80 2 75 \y 2 5 75 Monrovia 4 75 3 83 2^ 4 79 Glendora 3 83 2y 2 60 \y 2 67 1 4 70 Average 82 89 73 76 79 74 Had the fumigators indicated in the above table made their doses in proportion to the size of the trees, all the per cents given would have been 50. Thus, for instance, if the fumigator indicated as Covina (6) had followed the directions, supposing his tent to be 10 steres capacity, and required just the dose given, 4 ounces, then a tree twice as large should have received 8 ounces instead of 9, and one four times as large 16 ounces instead of 8. Likewise the smaller-sized trees should have received 2, 1, and \ ounces for the tents one half, one quarter, and one FUMIGATION DOSAGE. 11 eighth, respectively, of the average-sized tent, instead of 3, 2-J, and 2 ounces which they did receive. This fumigator used on an average 76 per cent as the ratio instead of 50 per cent as called for by the tables. Every fumigator thus reduces the dose for his largest trees and increases it for the smaller ones, so that if the practice shows an agree- ment in judgment upon any point this may be considered to be that one. It may be that this unanimity is explainable on the ground that it is difficult to conceive of the rate of increase in three dimensions when we really see but two. When looking at a tree one only sees the projected cross-section. The ratio which would express the difference between the volume and the area of the cross-section is about 67 per cent, a figure quite near the actual average ratio of the above table, 74 per cent. While it is thus possible that this variation of dose as between large and small trees may have arisen through an error in judgment, it may nevertheless be sound practice, as will be shown below. LEAKAGE OF GAS. Fumigation tents are never perfectly tight. The odor of the gas is always very evident outside of the tent, even in those that are tightest. The lightness of untreated canvas has caused many fumigators here and elsewhere to use tents that allow a very rapid escape of gas. This is upon the theory that the chemicals are cheaper than labor. Whether this is true or not it is evident that the dosage should be very different in tight and in open tents. Probably the efficiency of the gas ceases as soon as it reaches a certain dilution. The problem of dosage is then that of using enough material so that there will remain in the tent gas of the requisite strength to the end of the killing period. In order to learn how great in actual amount the leakage of the gas really was we secured the cooperation of Professor Colby of this Station, and determined the amount of cyanogen present in measured quantities of the air drawn from the tent at intervals. The results are as follows: Amount Present Amount Present in in First Period. Second Period Single tent, dry 0.07% 0.02% Single tent, wet 0.05% 0.01% Double tent, dry 0.21% 0.03% The tents used for the above tests were obtained through the kindness of Mr. C. M. Heintz, of Los Angeles, and Mr. W. F. Lawson, of Covina, and comprised some that had been in actual use and others that were new. They were of 6-ounce drilling, which is quite uniformly used for small tents. The old tents had been treated with a " tanning" solution. But little difference was noted between the new and the old tents in the escape of the gas. The gas was drawn slowly from the tent and repre- sents its average strength during the period. 12 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. The above experiments are not exactly comparable with each other, as the length of time in the two periods varied, though they represent approximately half an hour. The amount of chemicals used was suffi- cient to produce about 0.3 per cent gas. The rate of loss is therefore seen to be very great and rapid. The size of the tent used was quite small, only two steres in capacity, so that the rate of leakage would be much greater than in an average-sized tent. When the leakage is great, as in the above experiments, it becomes the most important factor to be considered in the dosage. Under any cir- cumstances the dose to be used should consist of the quantity of chemi- cals necessary to produce the desired density of the gas and enough more to allow for the leakage that will take place. The first item in- creases as the volume of the tent increases; the second, as the area of the canvas increases. In the case of two tents, one having half the volume of the other, the dose of the smaller tent should be one half, or 50 per cent, of that of the larger, if we considered only the first item. Since the area of canvas does not decrease so rapidly we would want a higher ratio to meet the requirements of the second item. This ratio is 70 per cent. The true ratio would seem, therefore, to be somewhere between 50 and 70 per cent, unless some other factor that we do not now suspect also enters into the calculation. This is considerably lower than the average of the actual practice. EFFECT OF MOISTURE. Fumigators differ fundamentally in their views as to the relation of moisture to the efficiency of fumigation. Some would be inclined to increase the dose and others to diminish it in foggy weather. This is a matter of theory rather than one of practice with them, however. Usually no attention is paid to the matter in the practical working of their outfits, except that when the tents become very wet and heavy fumigation is stopped because of the difficulty of handling them. The experiment given above with a wet tent shows that this may be a very important factor. The gas is so readily absorbed by moisture that it disappeared from the air within the tent more rapidly and com- pletely than through the walls of the dry tent. This is one of the points that should be carefully investigated. PRODUCTION OF THE GAS. The generation of the gas is a rather simple chemical reaction, but is not generally understood by fumigators. The chemical elements involved and their approximate atomic weights are as follows: Hydrogen ( H ) = 1 Sodium (Na) = 23 Carbon ( C ) = 12 Sulfur ( S ) = 32 Nitrogen ( N ) = 14 Potassium ( K ) == 39 Oxygen ( O ) = 16 FUMIGATION DOSAGE. ia If pure potassium cyanide were used the formula would read : CHEMICALS USED One Part Potassium Cyanide. by weignt. One Part 85 per cent Sulfuric Acid by volume or 1.8 parts by weight. Two Parts Water by volume or weight. K C N+H 2 S0 4 - H 2 7 H 2 39 12 14 2 32 64 2 16 2 16 • v ' v y ' * „ ' » v ' 65 98 18 7 X 18 no 7 726 Hydro- Cyanogen Gas. RESULT. Residue of Acid-Potassium Sulfate dissolved in HON H K S 4 1 12 14 1 39 32 64 Water. 8 H 2 2 1& 27 136 The material which is actually on the market and sold as pure 98 per cent potassium cyanide is really a mixture of potassium and sodium cyanides, and Professor Colby finds by analysis that it contains about 4 per cent of impurities and 30 per cent of sodium cyanide. Leaving out the impurities, the formula would be : One Part Sodium and Potassium Cyanide by weight. 85 One Part Two Parts per cent Sulfuric Acid by Water volume by volume or (1.8 parts by weight). weight. produces : 2KCN + Na C N + 3 H 2 S 4 + 3 H 2 + 22 H 2 = 39 12 14 23 12 14 2 32 64 2 16 2 16 * y ' » v > ^ , ' » y ' "• y ' 2X65 49 3 X 98 3 X 18 22 X 18 130 294 54 179 348 396 Hydro-Cyanic Acid Gas. 41 per cent of Cyanide used. and Residue dissolved in Water. Acid Acid Potassium Sodium Sulfate. Sulfate. Water. 3 H C N + 2 H K S 4 + HNa S 4 + 25 H 2 1 12 14 1 39 32 64 1 23 32 64 2 16 3X2T 2 X 136 120 272 25 X 18 81 392 450 In the above formulae the weight of the various substances is calcu- lated out by the atomic weights, and shows that the formula com- monly used — one part of cyanide, one of acid, and two of water — is correct whether one has the pure potassium cyanide or the mixed potassium-sodium cyanide now on the market. The sulfuric acid used usually runs nearer 90 per cent, which insures a sufficiency of the acid. PROPOSED DOSAGE SYSTEM. As the result of this study of fumigation methods we are in a position not only to call attention to the imperfections of the existing system of guesswork in the estimation of dosage, but to have some basis for definite recommendations. These recommendations must be considered as only tentative, since they are based chiefly on observations of actual field practice and the results have not been verified by careful deter- minations. 1 4 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. The base of the system of dosage suggested is that in which the prac- tice has most likely been correct, viz., the average dose of an average tent. The doses assigned to the average-sized trees with which the various fumigators were working is given in the diagram on page 6. By taking the average of these we obtain the starting point for the calcu- lation of the proposed scheme. This average is a 4^-ounce dose for a 14-stere tent. This might be considered a minimum dose, since it is possible that more have erred by using too little than too much. This dose, however, is nearly a third larger than the original recommendation of Mr. Morse in Bulletin No. 71 of this Station. All the recent recom- mendations for fumigation work in California have been weaker than the Morse table. The present practice, however, as we found it the last season, has certainly approved the increase. The ratio, or the relation between the dosage of tents of different size, is indicated in per cents in the diagram just referred to. Here the ratio given is that between the dosage of tents of such size that one has half the volume of the other. This ratio in the present practice is probably much too large, still it is more than likely that a figure above 50 per cent, which is the ratio that has heretofore been recom- mended, is really justifiable. The writer would suggest tentatively the ratio 70 per cent, the largest figure for which there appears to be any reason. This figure, though a great departure from former recommen- dations, is still below the ratio of the actual practice of about three fourths of our fumigators. The following table will show how much the dosage system here suggested differs from previous recommendations: Size of tent, in meters- Distance over tent. ._ 13.73 10.86 8.64 6.87 5.40 4.32 3.39 Distance around tent 18.30 14.48 11.52 9.16 7.20 5.76 4.52 Volume of tent, in steres 108 56 28 14 7 3.5 1.75 Dose, in ounces — By Morse schedule . 25.6 12.8 6.4 3.2 1.6 0.8 0.4 Present suggestion 12.7 8.9 6.2 4.3 3.1 2.2 1.1 PROPOSED SCHEME OF MEASURING. The measurement and calculation of the dosage according to any of the proposed schemes present some very considerable practical diffi- culties. The measurement of height and diameter required for most tables of dosage can not be made rapidly enough to be satisfactory. The measurement suggested in Bulletin No. 122 of this Station (that is, the distance over and that around the tent) can be taken with sufficient rapidity by the method described on page 4 of this Bulletin. It requires, however, considerable skill and activity. By either method there remains, after the measurements are taken, the necessity of calculation. To do this by mathematics is of course out of the question. The actual FUMIGATION DOSAGE. 15 volume can be determined quickly and accurately by the use of the diagram (Fig. 2) given above, and a series of curves could be made which would give the dose at once instead of the volume. It is very desirable, however, to avoid, if possible, the need of the use of tables and measuring apparatus. Very decided progress in this direction has been made by Mr. W. H. Payne, of Monrovia, who has invented a tent marked off with concentric rings giving the distance over the top of the tent in terms of the dose required. This scheme should work well if proper arrangements are provided for coordinating the second measurement, that around the tent. A scheme devised by the writer several years ago in Florida for use in fumigating against the white fly seems to solve the problem quite -*SS3CV=>Lr Fig. 6. Fumigation tents marked to indicate dosage. satisfactorily. It consists in making a series of parallel lines near two opposite edges of the tent, which are so distanced from the center point that they shall correspond with the dosage of a tree of the average shape. Upon these lines will be placed numerals indicating the dose, the circumference in yards (paces), and the difference (that is, the amount the dose must be varied), should the distance around be more or less than the amount indicated for an average tent. This plan would permit the estimation of the dosage with sufficient rapidity and a fair degree of accuracy. If the tent is not put on the tree so that its center is directly over the center of the tree, the same dosage line may not touch the ground on the two sides, but the average of the two will 16 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. give approximately the correct measurement. A lateral displacement will give no trouble if the rule is followed when more than one line touches the ground on one side, of using the one indicating the highest dosage. The following table gives the scheme of marking tents: Numerals to be marked on the lines. Distance from Center of Tent. Ft. In. 2 5 3 1 5 3 6 5 7 6 8 5 9 3 10 10 8 11 4 12 8 13 10 14 11 16 17 18 18 11 Ounces. Paces. \ Difference. K 3 .1 1 4 .2 IK 5 .3 2 6 .3 2K 7 .4 3 8 .4 sy 2 9 .4 4 10 .4 4^ 11 .4 5 12 .4 6 13 .5 7 14 .5 8 15 .5 9 16 .6 10 17 .6 11 18 .6 12 19 .7 This whole series of lines would not be all placed on any one tent ordinarily, but only those useful for the given size of tent. Thus, for a 20-foot tent the lines corresponding to a dose of 1-J to 4 ounces would be useful; for a 30-foot tent, 2| to 8 ounces, and for a 40-foot tent, 4 to 12 ounces would be about the range. The appearance of these lines on a tent is shown in Fig. 6. The use of the tent will be evident from the following example: Suppose the lines on the ground at the two sides of a tree showed 7 and 9 ounces, respectively, and the number of steps around the tent was 17. The correct dosage would be 9 ounces. The average between 7 and 9 would have indicated 8 ounces, but the distance around was two steps more than 15, the number opposite the 8 ounces, and the difference that should be added for each of these is 0.5 of an ounce. RESUME. The present study is the result of an extensive series of measurements to determine what the present actual fumigation practice is in the matter of dosage. The apparatus used for measuring tents was a wire line manipulated by means of a fishing-rod. The dimensions thus obtained were then plotted on cross-section paper, and the volumes obtained by the use of a system of curves. FUMIGATION DOSAGE. 17 A striking difference in the practice of fumigators of the different counties was noticed, corresponding somewhat with the history of fumi- gation practice in their regions. No fumigator was found who could make accurate estimates of the volume of a tent, showing that uniform results require that actual measurements be made. All fumigators agree in giving large trees a relatively heavier dose than a small tree receives per unit of volume. The rate of leakage, which has not heretofore been taken into consid- eration in planning schemes of fumigation dosage, was shown to be very large, and gives some reasons for the larger dosage of small trees. Moisture was shown to have a great influence on the gas content, but how it might affect dosage remains yet to be determined. The calculation of the reaction in the generation of the gas shows that the proportions of cyanide and acid commonly used are correct. A system of dosage based on the average of the measurements, and with a ratio approaching the actual practice, is proposed; and finally — A scheme is presented for marking fumigation tents so as to insure accurate dosage. REPORTS AND BULLETINS AVAILABLE FOR DISTRIBUTION. REPORTS. 1896. Report of the Viticultural Work during the seasons 1887-93, with data regarding the Vintages of 1894-95. 1897. Resistant Vines, their Selection, Adaptation, and Grafting. Appendix to Viti- cultural Report for 1896. 1898. Partial Report of Work of Agricultural Experiment Station for the years 1895-96 and 1896-97. J 1900. Report of the Agricultural Experiment Station for the year 1897-98. 1902. Report of the Agricultural Experiment Station for 1898-1901. BULLETINS. No. 115. Remedies for Insect and Fungi. (Revised.) 121. The Conservation of Soil Moisture and Economy in the Use of Irrigation Water. 125. Australian Saltbush. 127. Bench-Grafting: Resistant Vines. 128. Nature, Value, and Utilization of Alkali Lands. 129. Report of the Condition of Olive Culture in California. 131. The Phylloxera of the Vine. 132. Feeding of Farm Animals. 133. Tolerance of Alkali by Various Cultures. 134. Report of Condition of Vineyards in Portions of Santa Clara Valley. 135. The Potato-Worm in California. 136. Erinose of the Vine. 137. Pickling Ripe and Green Olives. 138. Citrus Fruit Culture. 139. Orange and Lemon Rot, 140. Lands of the Colorado Delta in Salton Basin, and Supplement. 141. Deciduous Fruits at Paso Robles. 142. Grasshoppers in California. 143. California Peach-Tree Borer. 144. The Peach-Worm. 145. The Red Spider of Citrus Trees. 146. New Methods of Grafting and Budding Vines. 147. Culture Work of the Substations. 148. Resistant Vines and their Hybrids. 149. California Sugar Industry. 150. The Value of Oak Leaves for Forage. 151. Arsenical Insecticides. ^ Copies may be had by application to the Director of the Experiment Station, Berkeley, California. «