m w* WS , \:ii "LI 5 R.ARY OF THE UNIVERSITY OF ILLINOIS di-, ' ~*^5 --^-^ r*^*? - 1 _^r fcJL "J7x i* ^-' m RCULATING^COPY: ^ T-^^SY^ - UNIVERSITY OF ILLINOIS Agricultural Experiment Station, URBANA, APRIL, 1902. BULLETIN NO. 71. EXPERIMENTS WITH INSECTICIDES FOR THE SAN JOSE SCALE. BY S. A. FORBES, STATE ENTOMOLOGIST. The "California wash" of lime, sulphur, and salt, and the "Oregon wash" of lime, sulphur, and blue vitriol, have been for many years the general reliance of the fruit growers [of the Pa- cific Coas.t for protection against the San Jose scale. In a letter to me dated October 22, 1901, Prof. C. W. Woodworth, of the Ento- mological Department of the University of California, said that "the lime, salt, and sulphur mixture is the sole dependence in this state for killing the San Jose scale;" and under the same date Prof. A. B. Cordley, of the Entomological Department of the Oregon Agricultural College and Experiment Station, wrote: "With us the lime, salt, and sulphur compound is a very satisfactory remedy for the San Jose scale, and is used very extensively. In fact, this and the lime, sulphur, and blue vitriol compound are practically 241 242 BULLETIN NO. 71. [April, the only ones used for winter sprays for this insect.' 1 As early as 1889 the California wash was the only winter remedy recommended for the San Jose scale by the Secretary of the State Board of Hor- ticulture, in the Annual Report of the Board for that year; and in 1896 Prof. John B. Smith, State Entomologist of New Jersey, who visited California for a special study of the San Jose scale and its treatment there, found the lime, salt, and sulphur mixture one of the "favorite insecticides" for that scale in California and on the Pacific Coast generally.* The introduction of these insecticides in the East has been long- delayed, probably owing 1 in large measure to unfavorable re- ports of experiments made in the Atlantic states. In articles pub- lished in Bulletin 3 of the U. S. Division of Entomology, issued in 1896, and in Bulletin 30 of the same series, 1901, p. 34, the re- ported failure of the California wash in the East is attributed to the frequent occurrence of rains shortly after the insec- ticide had been applied, and chemical testimony is brought forward in support of this supposition. USE OF CALIFORNIA AND OREGON WASHES IN ILLINOIS. In the fall of 1901, when an appropriation of $15,000 for in- secticide work on the San Jose scale became available to my office, I was embarrassed by the fact that no effective insecticide pre- viously used by us had been found free from serious liability to injure the more tender fruit trees, or at least their fruiting- buds. The peach and the plum were especially liable to serious damag-e by both the kerosene sprays and the whale-oil-soap solution, the first being injurious to the tree, and the second very commonly de- structive to the fruit buds and, of course, to the crop of the follow- ing- year. At this time I received from Professor Cordley, of Oreg-on, the above-mentioned letter, in which he sugg-ested that I should give the lime, sulphur, and salt compound a thorough test in Illinois, and further said that in Oregon, where this mixture is thoroughly effective, the climate is as moist during- the winter when the spray is principally used as in any part of the East. I had additional testimony to the same effect from a former student and assistant of mine, Mr. Fred .McElfresh, who informed me, after a year's experience in 'entomological work at the Oregon Agricultural College, that the weather of western Oregon is very similar to that of the greater part of Illinois. *Rep. Ent. Dept. N. J. Agr. Exper. Station, 1896, p. 551. IQ02.] EXPERIMENTS WITH INSECTICIDES FOR THE SAN JOSE SCALE. 243 Under these conditions I decided last fall to use the lime, salt, and sulphur mixture, standard in the Pacific states, for all our Illi- nois insecticide work on the peach and plum, preferring to take the risk of a possible inefficiency of the insecticide rather than the much greater one of serious injury to the orchard tree. The sea- son seemed favorable to the treatment, and highly encouraging re- ports came in from the field throughout the entire winter up to early March. At this time, in order to secure more precise and comprehensive information as to the value of the Oregon and Cali- nornia washes, I detailed one of my office assistants, Mr. E. S. G. Titus, to carry out a series of experiments with them under various conditions, and sent him to Sumerfield, in St. Clair county, where he remained for three weeks, supervising the treatment of the trees, and making counts of scales and other observations of the results. SECONDARY RESULTS OF THE EXPERIMENTS. It was the principal object of these experiments to test the ef- fects of rains on the two washes used, but other important results appeared in the outcome besides those immediately aimed at. Counts of dead and living scales on the check trees not treated and on the experimental trees before treatment, showed a surprising percentage of half-grown scales already dead, the ratio of dead young to living scales varying on different trees and on different parts of the same tree from twenty-one per cent, to sixty-nine per cent. This fact had already been observed in other localities where our insecticide work was in progress, and had, indeed, been noticed and reported as early as 1898 by another assistant of the office, Mr. E. B. Forbes, engaged in distributing to infested trees in southern Illinois the spores of a fungus parasite of the San Jose scale. This spontaneous death of many of the scales which might have been expected to pass the winter alive, was apparently due in great measure and in both instances to a severe drouth of the pre- ceding year. Consistently with this explanation the dead scales were most abundant on trees worst affected by the drouth, and on parts of trees to which the flow of sap would naturally be least. Another observation of importance to the investigator was made with reference to the action of the insecticide in loosening the scales of the insects killed by it. In most cases where the ap- plication took fatal effect the scales were so far loosened from the bark that they were easily rubbed off, and might be washed away in large numbers by an ordinary rain. As a consequence, if counts were made of dead and living scales upon a tree before treatment, and again after a treatment and after a heavy rain had fallen, the ratio 244 BULLETIN xo. ji. [Apri/, of living- to dead might be as great in the latter case as in the former. It will be seen that by overlooking- this circumstance an investig-ator might easily be led to very erroneous conclu- sions as to the effects of moisture on the insecticide. GENERAL FEATURES OF THE EXPERIMENTS. The actual effect of rains was experimentally ascertained by heavily spraying- the trees with water at selected intervals after treatment with the wash, and by making- careful counts of dead and living- scales in each case and comparing- the ratios so arrived at with those found in the beginning-. The trees sprayed with each mixture were treated exactly alike except as to the subsequent application of water, and in this latter respect the different trees received very different treatment. Some, for example, were watered but once, and that the next day after the application of the insecti- cide wash; and others were watered daily for the seven days next following- it. In order to avoid interference with the experiments by rains, which fell three times during- the fortnig-ht covered by the greater part of the experiments, some of the trees were covered by canvas tents at night and whenever rain threatened. GENERAL STATEMENT OF RESULTS. Details of all forms and variations of the experiment will be given further on, but it is sufficient for this general statement to say that the general averag-e result of a single spraying of twenty trees with lime, sulphur, and salt was the destruction of 90.6 per cent, of the scales when no water was applied within five days, and of 86 per cent, when water was used. The corresponding result of the application of lime, sulphur, and blue vitriol to fifteen trees, was the destruction of 93 per cent, of the scales without water, and 92.2 per cent, when water was applied within the first five days. PERIOD AND METHODS OF THE EXPERIMENTS. The experiments on which the above statement rests may be conveniently described in five lots: two with lime, sulphur, and blue vitriol; two with lime sulphur and salt; and one, a special ex- periment, with both these washes on trees covered by tents. Two of the four experiments above mentioned one with the California wash and one with the Oregon wash were begun March 3, and the other two (in which also both washes were used) were begun March 5. The tent experiment was begun on the 21st of the month. Observations on all the lots treated were continued until I9O2.] EXPERIMENTS WITH INSECTICIDES FOR THE SAN JOSE SCALE. 24$ March 25; that is, twenty-two days for the first two lots, twenty days for the third and fourth, and five days for the lot under tents. The experiments consisted of a single application of the insecticide in every case, with varying 1 subsequent treatments of the different trees with water. Frequent counts of dead and living- scales were made for all of the trees, no attention being paid in these counts to old scales, outworn and dead, but only to those whose size and immature character showed that they belonged to the new generation of the preceding fall. Counts of dead and living scales were made in all cases either before or shortly after the applica- tion of the insecticide spray. It was. in this way ascertained that an average of about fifty per cent, of the immature scales were al- ready dead on these trees before the insecticide was applied; and that the action of the insecticide was scarcely perceptible within the first twenty-four hours. EXPERIMENTAL TREES USED. Forty-three trees were used in all the experiments, twenty-five of them apple-trees and eighteen -peach. They varied in height from twelve to eighteen feet; in spread of top from eight to twenty feet; and in diameter of trunk from four to nine inches. The av- erage height was fourteen feet, and the average spread, thirteen. The general condition of these trees varied from "very poor" to "excellent," six of them being described as "very poor," eight, as "poor," sixteen, as "fair," ten, as "good," and three, as "excel- lent." Some of the peach-trees were more than half dead, and many of them in such a condition that the owners were about to remove them. The dry weather of the preceding summer had killed the young growth even on otherwise healthy trees, and in some cases much of the older wood had also died from drouth. All the trees were, of course, infested with the San Jose scale, eight- een of them badly so, and the others to a medium degree. WEATHER OF THE PERIOD. The weather of the experimental period was the ordinary variable weather of an Illinois March, the temperature at seven o'clock a. m. ranging from 18 F., on the 18th, to 54, on the 15th, and at noon, from 34, on the 18th, to 88, on the 25th. There was an unusual amount of wind from the southeast on not less than fourteen days out of the twenty-two. Rain fell on six days, and a light snow on one other. The first rain, on March 7, lasted for two and a half hours, but was very light about two gallons for each experimental tree according to Mr. Titus's estimate. The 246 BULLETIN NO. Jl. [April, temperature at the time was 56. On the ninth day after the begin- ning- of the first experiment (March 11) the weather was showery, with heavy mist most of the day, the temperature 60 to 64; and on the thirteenth day (March 15) a heavy shower of rain fell, with hail, for an hour in the afternoon, amounting to ten or twelve gal- lons to the tree. The 17th and 18th were cold 26 in the morning and 24 at noon on the 17th, and 18 in the morning and 24 at noon on the 18th. The wind blew strong and cold from the northwest, with a light snow on the first of these days. A slow drizzling rain fell on the 20tb, beginning at about five in the afternoon and continuing through the night and all the following day. The insecticide sprays were applied on the 3d, the 5th, and the 20th. March 3 was a partly cloudy day, with a cold raw wind from the east and northeast, the thermometer registering 30 at 7 a. m. and 40 at noon. The 5th was a clear day, with a northwest wind, fairly strong, the thermometer 30 at 7 a. m. and 45' at noon. On the 20th the wind was from the southeast, with a threat of storm which resulted in rain at five o'clock in the afternoon. The temperature was 34 at 7 a. m. and 57 at noon. PREPARATION OF THE INSECTICIDES. The insecticide washes were prepared in substantially the same manner. For the California wash, fifteen pounds of stone lime were slaked in a little very hot water, fifteen pounds of ground sulphur being slowly poured in during the slaking process with constant stirring of the mixture. This was then boiled for an hour, after which fifteen pounds of salt were added and the boil- ing continued for 'fifteen minutes longer. The whole was then poured into a barrel through a strainer, and enough boiling water was added to make fifty gallons. In the preparation of the Ore- gon wash a pound and a quarter of blue vitriol was used instead of the salt, the crystals of the blue vitriol being dissolved in hot water and the solution added slowly to the slaking lime. The ap- paratus used was a Morrill and Morley pump, with twenty-five 'feet of hose and a twelve-foot extension rod with a double Ver- morel nozzle. THE WATER SPRAYS TO TEST EFFECT OF RAINS. In wetting down the trees to imitate the effects of rain, fifteen gallons of water were used to a tree, as a rule, a double amount being occasionally applied as a variation of the experiment. For a tree of the average spread of thirteen feet, fifteen gallons of IQ02.] EXPERIMENTS WITH INSECTICIDES FOR THE SAN JOSE SCALE. 247 water was equivalent to a rainfall of a sixth of an inch, amounting to a sharp summer shower. The washing- and leaching- effect of the application was, however, greater than that of a correspond- ing shower, since the water spray was not distributed equally over the whole area covered by the tree top, but was made to wet the tree equally in all parts; the middle part of the tree much more freely, consequently, than the outer parts. It would doubtless be fair to say that the fifteen-gallon portion was equivalent in effect on the average experimental tree to a rainfall of a third of an inch, and the double portion, of course, to twice that amount. The time taken for the application of fifteen g-allons varied, according to the weather and the size of the tree, from twenty minutes to thirty or thirty-five, and for the thirty-gallon application it was never less than an hour. The water in all cases dripped freely from the trees for some time after spraying- ceased, carrying with it so much of the insecticide in solution that the drip was of about the color of the original mixture. The applications of water were varied systematically as to number, to frequency, and to period of time between the insecti- cide operation and the first general wetting 1 . Tree No. 1, for ex- ample, was wet every day for a week, commencing- the next day after the California wash was applied; tree No. 2 was wet but once, and that the day after insecticide treatment; tree No. 3 was sprayed on the 3d with the California wash, and with water on the 6th and every other day thereafter for three days; tree No. 6 was sprayed but once, and then with thirty gallons of water one week after insecticide treatment; and tree No. 9, the same, except that the water was applied at the end of two weeks. Further particu- lars may be obtained from the detailed accounts of the experi- ments. EXPLANATION OF TABLES. The four tables in the text have been prepared to present in summary form the detailed results of the treatment for each tree as shown by successive counts of scales on selected sample twigs and branches. Ag-ainst the number of each tree is placed for each date on which special observations were made, the number of scales counted and the percentage of scales killed by the insecticide up to that time. The first count shows always the percentage of scales found alive at the time of treatment. The last column in each table shows the final effect of treatment in the form of a gen- eral average of all the percentages of scales killed, excluding only the first seven days subsequent to the insecticide treatment. At the bottom of each table is a series of data for the entire lot of 248 BULLETIN NO. Jl. [April, trees, corresponding- in form to those given in the body of the table for each tree. EXPERIMENTAL DETAILS. First Lot of Trees. California Wash Nine apple-trees sprayed with lime, sulphur, and salt on the 3d day of March. Weather partly cloudy, with cold raw wind from the east-northeast; temperature, 30 9 at 7 a. m. and 40 at noon. Dead and living- scales were first counted on these trees the following- day, March 4. Although the fact was not known at the time, it became apparent later by comparison of percentag-es of scales on these trees with those found on check trees and on other lots counted before insecticide treatment that no discoverable effect of the insecticide had been produced at the time this first count was made. If any scale insects had been killed so soon, their appear- ance had not yet sufficiently changed to indicate the fact. The percentag-es found on this first day are, consequently, to be taken as indicating- the ratio, before treatment, of dead and living- scales among- the young- of the preceding year. One thousand three hundred and fifty such scales were counted in all, and 52 per cent, of these were alive, 48 per cent, having died from unknown causes, in most cases probably from drouth. In determining- the effect of the insecticide under the varying- conditions supplied, this first count of living- scales was made the starting- point for the calculation of the percentag-es of scales killed; that is, if only 50 per cent, of the scales were found alive at the beginning- of the experiment, the destruction of scales by the insecticide was figured on this 50 percent., those dead in the begin- ning- being-, of course, ignored. Counts were made upon carefully selected specimen twigs or branches, the number counted each time varying- from 100 to 400, and the totals for each tree, from 300 to 1,350. The total number of scales counted from this lot on nine trees was 9,000. The effect of the insecticide was only gradually made mani- fest, and was, as a rule, not fully produced until about the tenth day, although the difference between the final result and that ap- parent at the end of the first week was really but small. Conse quently, in describing- the different features of the experiment, the average of the counts after the first week will be taken to express the final effect of the insecticide in destroying the San Jose scale. As these various trees were treated subsequent to the insecti- cide spray by an application of various amounts of water at differ- ent intervals, it will be necessary to discuss each tree separately. J9O2.] EXPERIMENTS WITH INSECTICIDES FOR THE SAN JOSE SCALE. 249 LOT I. SPRAYED WITH LIME, SULPHUR, AND SALT, MARCH 3. N N V. a S u cti s u rt 2 03 s S a S a s rt s CS s rt s rt s ct 5 It '5 4 20 27 2 9 31 32 33 35 36 No. counted . . Per ct. alive . . 100 A2 2OO 400 2OO 250 850 Per ct. killed. . 83 8? 80 68 100 78 25O No. counted . . 7OO IW Per ct. alive . . 47 Per ct. killed. . Q2 08 200 95 450 No. counted . . Per ct. alive . . 2OO ?6 150 300 2t;o Per ct killed. . 62 2OO 80 78 88 150 83 750 No. counted . . Per ct. alive . . 200 4.2 200 200 2OO Per ct. killed.. No. counted . . Per ct. alive . . 300 -17 .... 80 2OO ICO 92 .... 87 2^O 98 93 200 93 450 Per ct. killed. 78 300 83 O2 78 300 85 IOOO No. counted . . 300 300 200 2OO Per ct. killed.. No. counted . . Per ct. alive 30O 4C 69 2OO .... 86 300 .... 79 2OO 89 .... 87 300 85 800 Per ct. killed.. No. counted . . Pet ct. alive 2OO 18 20O 70 200 80 300 .... 300 87 . 2OO 95 300 87 IIOO Per ct. killed.. No. counted . . Per ct. alive . 2OO ; I 62 300 00 2OO :: 00 200 99 .... .... 91 200 97 200 94 600 Per ct. killed. . 51 .... 85 .... 97 .... .... 94 99 97 ^ 5 I H ) No. counted . . Per ct. alive . . 2OOO 42 500 IO5C IOOO 1200 650 700 500 400 400 400 20OO 6250 Per ct. killed. . 56 71 84 86 93 86 88 84 94 93 89 89 remarked, that scales kil led the first day, if any, do not sufficient- ly change in appearance within that time to suggest the fact. Subsequent counts of scales were made for this lot on eleven later dates, the number counted, as before, ranging from one hundred to four hundred, and amounting for the lot to 10,500 specimens. Tree No. 4. An apple-tree, sixteen feet high, with a nine-inch trunk and a twelve-foot top ; in fair condition, but badly infested by the scale. This tree received but one water treatment, and that on the 7th of March, two days after the insecticide application and on the same day as the first light fall of rain. Fifteen gallons 1 902.] "EXPERIMENTS WITH INSECTICIDES FOR THE SAN JOSE SCALE. 253 were applied, and approximately two gallons must be added for the rainfall. Scales alive in the beginning 1 , 42 per cent. ; 83 per cent, of these killed on the sample for the fifth day, with an average of 78 per cent, as the final effect of the insecticide. Tree No. 20. A peach-tree, twelve feet high, with a six-inch trunk and a nine-foot spread of top ; in very poor condition, though but moderately infested by the scale. No water except the natural rainfall. Forty-seven per cent, of the scales were alive in the be- ginning ; 92 per cent, of these were dead on the thirteenth day, when the first subsequent count was made, and 98 per cent, on the sample for the twentieth day, the final average effect being reckoned at 95 per cent, destroyed. 7"rce No. 27. An apple-tree, fifteen feet high, with an eight- inch trunk and a seventeen-foot top ; in good condition, moderately infested with the scale. This tree was sprayed with water but once, and that five days after the insecticide application. Thirty- six per cent, of the scales were alive in the beginning; 62 per cent, of these were dead on the fourth day and 80 per cent, on the fifth, the average final effect being reckoned at 83 per cent, destroyed. Tree No. 29. An apple-tree, twelve feet high, with a seven- inch trunk and a fifteen-foot top ; in bad condition, and heavily in- fested. Twice treated with water, once on the fifth day after the insec- ticide spray and once on the tenth, in each case with fifteen gallons. Forty-two per cent, of the scales alive at the beginning of the exper- iment; 80 per cent, of these dead on the.fourth day and 92 per cent, on the tenth day ; the average final effect, the destruction of 93 per cent, of the scales. Tree No. j/. AD apple-tree, twelve feet high, with an eight- inch trunk and a nineteen-foot top; in good general condition, and moderately infested by the scale. Once treated with thirty gallons of water, on the next day after the application of the insecticide spray. Thirty-seven per cent, of the scales were alive in the be- ginning ; 78 per cent, of these were dead on the fourth day and 83 per cent, on the fifth; the final average effect of the insecticide, 85 per cent, destroyed. Tree No. J2.A peach-tree, twelve feet high, with a six-inch trunk and a nine-foot top ; in fair general condition, but heavily infested. Treated with fifteen gallons of water a day for three days in succession, beginning the next day after the insecticide spray was applied. The second of these treatments coincided with the first day's rain. Forty- four per cent, of living scales at the be- ginning ; 69 per cent, of these dead on the fourth day and 86 per 254 BULLETIN NO. 71. [April, cent, on the tenth, according- to the sample for that day ; the final average effect, the destruction of 85 per cent. Tree No. jj A peach-tree, nine feet high, with a three-inch trunk and an eight-foot top ; in good condition, moderately infested by the scale. Sprayed twice in succession with fifteen gallons a day, following- immediately upon the insecticide treatment, the second application coinciding- with the first day's rain. Forty- five per cent, of the scales alive at the start; 70 per cent, of these dead on the fourth day and 80 per cent, on the tenth; final averag-e effect, the destruction of 87 per cent, of the scales. Tree No. jj. A peach-tree, fifteen feet hig-h, with five-inch trunk and a twelve-foot top; in poor condition, and moderately in- fested by the scale. Treated but once with water, and that on the tenth day after the experiment began, this treatment coinciding with the third day's rain. Thirty-eight per cent, of the scales alive at the time of the application of the insecticide; 62 per cent, of these dead on the second day and 90 per cent, on the fifth, with an average final destruction of 94 per cent, of the scales. Tree No. 36. A peach-tree, fifteen feet high, with a six-inch trunk and an eight-foot top; in poor condition, and heavily infested. Treated with water twice, once on the day following the insecti- cide treatment and once on the tenth day of the experiment, the last treatment coinciding with the third day of rain. Fifty-one per cent, of the scales alive in the beginning, and 51 per cent, of these dead on the second day after insecticide treatment; 85 per cent, dead on the fifth day, with a final average destruction of 97 per cent, of the scales. Taking this group of nine trees as a whole and averaging all statements concerning them, it appears that 42 per cent, of the scales were alive when the experiment began; that 56 per cent, of these had been killed by the treatment by the second day thereafter, 71 per cent, by the fourth and 84 per cent, by the fifth; and that the final average effect was approximately 89 per cent, destroyed. To this lot it will be convenient to add for discussion two other trees sprayed with lime, sulphur, and salt on the 7th of March, which, it will be remembered, was the day of the first rainfall occurring in the experimental period. These trees re- ceived no water treatment, but were intended as checks on the other experiments. Tree No. 38. The first of these was a peach-tree, nine feet high, with a five-inch trunk and a ten-foot top. It was in excel- lent condition, and only moderately infested. Thirty-eight per cent, of the scales were alive on the day preceding the insecticide 1902.] EXPERIMENTS WITH INSECTICIDES FOR THE SAN JOSE SCALE. 255 application, and on the day following 1 the treatment 31 per cent, of these were dead. No other count was made upon this tree until the eleventh day, when 96 per cent, appeared to have been killed. The final general effect was an average of 89 per cent, of the scales destroyed. Tree No, jg. The second tree of this pair was also a peach- tree, about nine feet high, with a five-inch trunk and a ten-foot top. It was in excellent general condition, and moderately in- fested. Only 27 per cent, of the scales were alive when the experi- ment began ; 29 per cent, of these were dead by the second day after treatment and 84 per cent, by the third day ; and the gen- eral final effect averaged 91 per cent, of the scales destroyed. GENERAL RESULTS OF EXPERIMENTS WITH LIME, SULPHUR, AND SALT. An analysis of the data contained in the above descriptions of Lots 1 and 2 and in the tables of percentages for those lots ena- bles us to distinguish two groups of trees ; those which received some treatment of water within five days after the insecticide ap- plication, and those which, if treated with water at all, did not receive it until the principal effect of the insecticide had already been produced. There are eleven trees in the first group, namely, 1, 2, 3, 4, 5, 27, 29, 31, 32, 33, and 36, and nine trees in the second, namely, 6, 7, 8, 9, 10, 20, 35, 38, and 39. The average final effect of the insecticide upon the nine trees of the second group was the destruction of 90.6 per cent, of the scales, and the corresponding destruction on the eleven trees of the first group was 86.1 per cent., making a difference of 4.5 per cent, due to the action of water on the insecticide when applied within five days after the original treatment. In other words and more generally stated, it may be said that in these experiments the effect of thoroughly watering the treated tree during the first five days after the experiment began, was to diminish the destructive effect of the insecticide by approximately 5 per cent. If, regardless of this difference, we take these twenty trees as a group, we find that 48 per cent, of the young scales of the pre- ceding year were dead when the experiment began ; and that 43 per cent, of these were killed by the second day after treatment, 60 per cent, by the third, 84 per cent, by the fifth, and 86 per cent, by the sixth. The average effect of the insecticide, as shown by counts made from the seventh to the twenty-second day, amounted to 88.4 per cent.; or, if we include only the counts from the tenth to the twenty-second day, it stands at 89 per cent. 256 BULLETIN NO. J\. [April, LOT III. SPRAYED WITH LIME, SULPHUR, AND BLUE VITRIOL, MARCH 3. il oo o N N N P4 rn N -t- M u-i 1/1 N (S a % rt % 03 s ct 2 a) 5 Rt E c9 a S n a & tt & a 2 18 21 23 24 26 28 30 22 No. counted . . Per ct. alive . . 300 47 200 . 300 400 300 .... 200 200 1 100- Per ct. killed . No. counted . . Per ct. alive . . 100 ?! 15 IOO 83 IOO 89 150 150 87 91 87 2OO 88 500 Per ct. killed . No. counted . . Per ct. alive . . 300 40 o 300 90 98 96 200 97 300 97 800 300 Per ct. killed . No. counted . . Per ct. alive 6q 88 02 88 20O 89 550 2OO 4.2 206 200 150 200 Per ct. killed . No. counted . . Per ct. alive 300 j-l 38 2OO 200 92 2OO 92 300 00 300 9 6 2OO 93 800 Per ct. killed . No. counted . . Per ct alive 250 eg 35 68 84 150 2OO 93 200 97 87 2OO 92 600 Per ct. killed . No. counted . . Per ct. alive 7 6 300 91 oo 83 3OO 9i IOOO 200 AA 200 200 300 Per ct. killed . No. counted . . Per ct. alive 300 AA 9 2 3OO 86 300 .... 83 200 93 150 92 2OO 89 850 Per ct. killed . 88 00 98 94 98 95 - ( } ) H ( No. counted . . Per ct alive 1950 AA 700 500 1550 750- IOOO 800 400 500 950 I800 6200 Per ct. killed . 22 66 86 93 90 93 91 9i 94 91 9i March 4; 81 per cent, of these dead on the fifth day and 92 per cent, on the twelfth, with a general final average of 93 per cent, destroyed. The corresponding tree of the other lot is No. 9, which shows a final average destruction of 89 per cent. 1902.] EXPERIMENTS WITH INSECTICIDES FOR THE SAN JOSE SCALE. 259 Tree No. 77. An eighteen-foot tree, with a nine-inch trunk and an eighteen-foot top; in poor condition, and badly infested. A check tree, receiving 1 no water treatment, the effect of the insec- ticide being- consequently modified only by the three rains de- scribed. Forty-one per cent, of the scales alive in the beginning 1 ; 68 per cent, of these dead in three days and 95 per cent, in twelve, with a general average of 95 per cent, finally destroyed. This, it will be noticed, is the same final average result as that of the com- panion experimental tree, No. 10. Fourth Lot of Trees. Oregon Wash. This lot is essentially a duplicate of Lot 2 except with re- spect to the insecticide treatment, which was identical with that of Lot 3, and also with respect to the number of trees made use of, which was eight in this lot and nine in Lot 2. All variations of experiments with Lot 2 are represented in Lot 4 with the exception of that for No. 29. Tree No. 18. A sixteen-foot apple-tree, with a nine-inch trunk and a twenty-foot top; in fair general condition, but badly infested by the scale. Treated, like No. 4 of Lot 2, with a single applica- tion of fifteen gallons of water on the second day after the experi- ment, coinciding with the first shower of rain. Forty-seven per cent, of the scales alive when the insecticide was applied; 15 per cent, of these dead on the second day and 83 per cent, on the fifth, with a final average destruction of 88 per cent. The correspond- ing ratio for the companion tree, No. 4, was 80 per cent. Tree No. 21. A fifteen-foot peach-tree, with an eight-inch trunk and an eighteen-foot top; in good condition, and but moder- ately infested, This received the same water treatment as No. 27 of Lot 3, namely, one application of fifteen gallons of water on the fifth day after the insecticide. Thirty-one per cent, of the scales were alive in the beginning. None of them appeared to have been killed on the second day thereafter, but 90 per cent, of these were dead on the fifth day, and 98 per cent., according to the count made, five days thereafter. The general final average was 97 per cent, destroyed. The corresponding ratio for the companion tree, treated with the California wash, is 82 per cent. Tree No. 22. A peach-tree, thirteen- feet high, with a six- inch trunk and a twelve-foot spread; in poor condition, though but moderately infested. Treated but once, and that on the tenth day after the insecticide application, fifteen gallons of water being used. The corresponding tree of the second lot was No. 35. Forty-four per cent, of the scales alive in the beginning; 88 per 260 BULLETIN NO. Jl. [Apri/, cent, of these dead on the fifth day, and 90 per cent, on the thirteenth, with a final average ratio of 95 per cent, destroyed; this to be compared with a 94 per cent, average of the companion tree. Tree No. 23. A fifteen-foot apple-tree, with an eight-inch trunk and a fifteen-foot top; in poor condition, moderately infested. This, like 32, treated with three daily water sprays of fifteen gal- lons each on three days immediately following the insecticide treatment a duplicate in this respect of No. 32 of the second lot. Forty-nine per cent, of the scales alive in the beginning; 65 per cent, of these dead on the fourth day and 88 per cent, on the thirteenth, with a final average destruction of 89 per cent, that of the companion tree, treated with the California wash, being 85 per cent. Tree Xo. 2+. A sixteen-foot peach-tree, with a six- inch trunk and a nine-foot top; in fair condition, moderately infested. Treated on two successive days immediately following the insecti- cide application with fifteen gallons of water on each day, the second of these treatments coinciding with the first day of rain. Forty-two per cent, of the scales alive in the beginning; 38 percent, of these dead on the second day and 92 per cent, on the fifth, the average final result being the destruction of 93 per cent, of the scales to be compared with 87 per cent, finally destroyed on the companion tree, No. 33, treated with the California wash. Tree No. 26. A twelve-foot peach-tree, with a six-inch trunk and an eleven-foot top; in very poor condition though but moder- ately infested. Treated, like No. 36 of the second lot, with fifteen gallons of water on the day following the insecticide application, and another fifteen gallons on the ninth day thereafter, that is, the 15th day of March. This last treatment coincided with the third rainfall. Thirty-three per cent, of the scales alive at first; 35 per cent, of these dead on the second day, 68 per cent, on the fourth, 84 per cent, on the fifth, and 93 per cent, on the fifteenth when the next succeeding count was made. A general final average of 92 per cent, of the scales destroyed. The companion tree of the second lot gives a ratio of 97 per cent, finally killed. Tree Xo. 28. A fourteen-foot peach-tree, with a five-inch trunk and a ten-foot top; in very poor condition, though but mod- erately infested with the scale. This tree was reserved as a check upon the experiment, without water treatment of any kind, com- paring in this respect with No. 20 of Lot 2. Fifty-eight per cent, of the scales were alive on it in the beginning; 76 per cent, of these were dead on the fifth day, and 91 per cent, on the tenth, I902.J EXPERIMENTS WITH INSECTICIDES FOR THE SAN JOSE SCALE. 26l the final average destroyed being- 91 per cent. The corresponding ratio for the companion tree of the previous lot was 95 per cent. J^ree No. jo. A twelve-foot apple-tree, with an eight-inch trunk and a fourteen-foot top; in good condition, and but moder- erately infested. Treated but once, and that with thirty gallons of water on the next day after the application of the insecticide. Forty-four per cent, of the scales alive in the beginning ; 92 per cent, of these found dead on the sample examined on the fifth day after treatment, the final average effect being the destruction of 89 per cent, of the scales. On tree No. 31, corresponding to this in the second lot, the average final ratio was 84 per cent, destroyed. COMPARISON OF VALUES OF OKEGON AND CALIFORNIA WASHES. Comparison of Lot 3 with the companion trees similarly treat- ed in Lot 1 brings out very definitely the relative advantage of the Oregon wash. The general average of the ratios of final destruc- tion is 93 per cent, for the Oregon wash and 87 per cent, for the lime, sulphur, and salt. If we limit the comparison to the three pairs of trees which received the water treatment within the first five days after the application of the insecticide, that is, to Nos. 1, 2, and 3 of Lot 1, and to 1 1, 12, and 13 of Lot 3, we find that in the latter 94 per cent, of the scales were finally killed, and in the former only 82 per cent. an unmistakable indication that the Oregon wash was not at all affected in these experiments by water treatment ; while the effect of the California wash was considerably reduced, a clear difference of 12 per cent, of effectiveness in favor of the Oregon wash. , Comparing next the general averages of final effects shown by the ratios for corresponding trees of Lots 2 and 4, contrasting thus with respect to these two lots the advantages of the California and the Oregon wash, we find them to be as 88 per cent, and 92 per cent, respectively a difference of 4 per cent, in final effect shown by this group of experiments in favor of the Oregon wash. Bringing together the two lots representing each insecticide treatment and combining averages for the two insecticides as rep- resented by the four lots of trees, it appears that 92 per cent, of the scales were destroyed by the Oregon -wash on fifteen trees as compared with 87 per cent, on fifteen trees identically treated after spraying with the California wash a difference of 5 per cent, in favor of the former treatment.* *The slight difference between this statement and the one on p. 244 is due to the fact that in the former certain trees treated with the California wash were included which were not exactly duplicated as to treatment by any of those treated with the Oregon wash. 262 BULLETIN NO. Jl. [April, THE TENT EXPERIMENT. All the preceding- experiments were intended to test the ef- fect of artificial applications of water on the action of the two in- secticides, these applications being- made in a way to simulate the effects of rainfall. They were interfered with slightly by the three periods of light rain, the effects of which could not be clear- ly separated from those of the artificial treatment. With a view to a test of the effects of rainfall, a small experi- ment was undertaken in which two trees one treated with the California wash and the other with the Oregon wash were cov- ered with heavy canvas during the night and whenever rain threat- ened by day. Two other trees were similarly treated and left at all times exposed, and still two more, selected because of their close correspondence to the experimental trees, were reserved with- out treatment, as checks. This experiment was begun March 20. The trees selected (the only ones remaining available) were peach- trees on high ground and light soil, heavily infested, and in very poor condition. The drouth of the preceding season had affected them very seriously, the young wood being largely killed, and on- ly 29 per cent, of the young scales on them being still alive. The weather was favorable to the experiment. The insecti- cides were applied on the afternoon of March 20, and a slow fine rain began at 5 p. m. of the same day and continued until nine o'clock and for an unknown time into the night, Rain fell in a con- tinuous drizzle, broken by showers, the whole of the following day, March 21, to an amount estimated by Mr. Titus at more than thirty gallons per tree. The temperature of the 20th was 34 at 7 a. m. and 57 at noon; that of the 21st was 44 at 7 a. m. and 52 at noon, the wind from the southeast both days. Observations on this experi- ment continued only until the 25th, but counts of the scales were made daily up to that time 3,000 scales for the four experimental trees, and 2,050 for the two checks. In thi s small experiment no differences of any significance were made out in the action of the insecticides, the total general effect being the destruction of approximately 95 per cent, of the scales, and variations from this average in the individual trees being too slight to take into account. So far as any conclusion can be drawn from an experiment on so small a scale, we can only infer that a rainfall such as described, occurring at the time of the insecticide treatment, would have no appreciable effect on the action of either of the washes. The apparent extraordinary efficiency of the 1902.] EXPERIMENTS WITH INSECTICIDES FOR THE SAN JOSE SCALE. 263 washes on these trees is plausibly explained by Mr. Titus as con- nected with the poor condition of the trees and the probable con- sequent low vitality of such of the scale insects as remained alive. EFFECTS OF RAIN AND WATER SPRAYS IN WASHING OFF DEAD SCALES. Noticing- that many scales were loosened and washed away af- ter insecticide treatment of the trees, Mr. Titus made some care- ful counts from day to day of selected lots of scales on the experi- mental trees to determine the circumstances and the ratio of their diminution in numbers. Selecting-, for example, a definite part of a branch, counting- a hundred scales on it when the insecticide was applied and marking 1 the area occupied by them, he counted them each day thereafter for several days and thus arrived at an exact conclusion as to the effect of the fluid applications and the incidental rains. Thus, on No. 1, 300 scales counted March 3 were reduced to 188 by March 15 a loss of 37 per cent. On No. 11, 400 scales were reduced in the same time to 223 a loss of 22 per cent. Both these trees, it will be remembered, were sprayed with the insecticide March 3, and daily thereafter for one week with fifteen g-allons of water. On No. 3, 100 scales were reduced in eight days to 72 a loss of 28 per cent., this tree having- been three times sprayed, with fifteen gallons of water each time. On No. 6, sprayed once with thirty g-allons. the loss was 25 per cent, in eight days; and on No. 14, receiving- the same treatment except that the insecticide used was the Ore- gon instead of the California wash, the loss for the same period was 11 per cent. No. 21, sprayed also but once, with 15 g-allons of water, lost 20 per cent, of its scales in seven days; No. 42, exposed to rains for a day and a nig-ht, lost in five days 11 per cent, of its scales; and No. 43, similarly exposed, lost 15 per cent. The check trees 40 and 41, on the other hand, kept without treatment of any kind, lost within five days but four scales out of five hundred counted. It was further apparent from observations made in the field that a brief but hard and dashing- rain would detach many more scales than a light rain longer continued and that a fine misty rain did not loosen the scales at all. PRACTICAL CONCLUSIONS. The foreg-oing- described observations and experiments gx> to show that the Oregon wash of lime, sulphur, and blue vitriol, pre- pared as described on p. 246, is a valuable insecticide for winter 264 BULLETIN NO. Jl. [April, use in the climate of Illinois for the destruction of the San Jose scale; that its full effect will be produced in about a week; and that frequent short rains will not noticeably diminish or delay its ac- tion, even when they come within the first five days after the in- secticide treatment. It is entirely harmless to any leafless tree, and hence may be freely used in winter (but in winter only) for all kinds of trees, shrubs, and vines. The California wash of lime, sulphur, and salt, prepared as described on p. 246, is a little less effective than the Oregon wash as a scale destroyer, and is considerably more likely to deteriorate after application if exposed to rains within the first few days. Otherwise its effects and characteristics are very similar to those of the Oregon wash, It should be generally known that both these washes corrode brass and copper rapidly, and that consequently an iron pump may be used to better advantage in spraying- them than one made in part of brass. With respect to the comparative effectiveness of these washes and the better known whale-oil soap and coal-oil mixtures we have as yet no accurate knowledge. There is nothing to indicate, how- ever, that the former are less effective here than on the Pacific Coast, where they seem to have been found very satisfactory in the hands of the ordinary orchardist for the destruction of the San Jose scale. Over both the latter applications they have the very great advantage that they are harmless to the tree, and that they do not endanger the crop of the following year. They are also de- cidedly cheaper than either the whale-oil soap or the kerosene emul- sion. In our winter's work the cost of the materials for these various mixtures has been $1.12 per hundred gallons of the Oregon and the California washes ; $2.80 per hundred gallons of kerosene emul- sion, diluted to contain twenty per cent, of kerosene ; and $6.50 for the same quantity of the whale-oil soap solution, at the usual strength of two pounds to the gallon of water. p,l > -^ / -AO^*-.! "OfV ;i l-C V /"", U " I' .. V^BKT ' , ^< ' r.V, # Mf^J^L^ J_ Mr^rv, Jit; KU\^ -s VJ ^ j ^ 1N X "-*F^ ?-sxj t>o* -w .^. ^T r^n^i ^.^o, &rt ^ Tkl ^W^ iwmlpj ^V>voZ v ^/s^B^^J- m^AtM *&& i*kJ^^^Ei ^Sit). 6 - k^2e>,f ^ UNIVERSITY OF ILLINOIS-URBANA