m< A ;, University of Illinois M Library at ^ Urbana-Champaign- '&&!$ ^-rmk^m^ '"%*» •j^1 »\x i &msmKBiBUt . \^j' v • "3*. /A" m*^ '^ ^x^h\ x: 30 1 2 Columns 1 2 3 4 5 6 Plot Times spray- ed Trees used Apples picked Injured per cent. No. C't'd Date Bushels Number [, Check Exp'er. 0 4 115 111 4 4 S. 16-20 S. 16-20 15.5 23.9 2,617 3,308 92.2 28.59 II, Check Exper. 0 6 34 32 3 3 Jl. 26-29 Jl. 26-29 11.4 16. 2,593 3,782 21.4 103 3 Ill, Check Exper. 0 6 20 20 3 3 S. 17 S. 17 16.25 22. 2,770 3,063 95.6 30.7 4 IV, Check Exper. 0 8 145 119 (9)4 4 Jl. 15 S. 16-20 6.44 24.44 1,540 3,198 91.1 185 270 BULLETIN No. 108. [May, CURCULIO SPRAYING EXPERIMENTS. — Continued. Sections 1 Columns 7 8 9 10 11 12 Plot Injuries prevented percent. Yield increased per cent. Bushels Value increased times No. 1 No. 2 No. 8 5 6 I, Check Exper. 69. 54. 1.5 17.16 6.2 5.5 7.8 1.16 2.75 II, Check Exper. 48. 40. 7 Ill, Check Exper. 68. 34. .75 12.06 3.75 3.25 11.66 6.66 2.5 8 IV, Check Exper. 80. Orchard I (Plot /.). — By an examination of this table it may be seen (Section i, Columns i to 5) that all the apples on 4 trees of Plot I. out of in of the Ben Davis variety which had been sprayed four times with arsenate of lead, were picked, measured, counted, and carefully examined between the i6th and the 2Oth of September, and that all the apples on 4 other trees of this plot out of 115 Ben Davises which had been left unsprayed as a check, were also picked, measured, counted, and similarly examined at the same time. These two lots of 4 trees each had been so selected at the beginning of the experiment from the whole number in each lot as to make the check lot the nearest possible duplicate of the lot which had been sprayed, except, of course, in the mere matter of spraying*. SPRAVED -4 TIMES NOT SPRAYED A • 4- • • . * . i i + • i [•••*••• • ^ • ^ A • -A- • -^ • -^ • ^ • ^ i • * ORCHARD NOI. APPL-ES COUNTED FROM STARRETD TREES *The four sprayed trees used for comparison with the four check trees are those starred in the sixth row from the middle line of the orchard. The four trees used as checks are among1 those starred in the fifth and sixth rows from the middle line. 1906.] SPRAYING APPLES FOR THE PLUM-CURCULIO. 271 The 4 trees not sprayed yielded 15.5 bushels of apples, and the 4 trees sprayed yielded 23.9 bushels (Section i, Column 4), the bulk of the yield being thus 54 per cent, greater for the sprayed trees than for those unsprayed (Section 5, Column 8). In other words the trees which had been treated, yielded one and a half times as large a quantity of apples as those which had not been sprayed. The number of apples from the 4 trees not treated (Column 5) was 2,617, while that from the trees treated was 3,308 — a difference of 26 per cent, in favor of the sprayed trees. That is, the sprayed trees bore a fourth -more apples than those which had not been sprayed. We should notice, in passing, that the apples from the trees not treated ran 169 to the bushel, and that those from the treated trees ran 139 to the bushel — a difference of 21 per cent, in average size of fruit in favor of the sprayed trees. That is, the ap- ples on the trees which had been sprayed were one fifth larger, on an average, than were those from the other trees. All these differences were apparent without any special examina- tion of the fruit with reference to injuries by curculios. When these curculio injuries were distinguished and tabulated (Column 6), it was found that 92.2 per cent, of the apples on the unsprayed trees had been injured by curculios making feeding-pits, egg punctures, or both, and that 28.6 per cent, of' the apples on the sprayed trees were so injured. A simple calculation from these data shows (Section 5, Column 7) that 69 per cent, of the apples which would have been in- jured if no treatment had been applied, had been protected from injury by the arsenate spray. Next, the total product of both lots of trees was separately and very carefully graded as No. I's, 2's, and 3's, by the standards of the American Apple Growers' Association adopted in 1903, (Section 5, Columns 9, 10, and n,) with the result to show that the 4 check trees yielded il/2 bushels of No. I's, and the 4 sprayed trees, 17.16 bushels; that the check trees yielded 6.2 bushels of No. 2's, and the sprayed trees, 5^ bushels; that 7.8 bushels of No. 3's were borne by the check trees, and 1.16 bushels by the trees which had been sprayed. (See Plates I. and II.) According to the best estimate we can make of the market values of these three grades, if the No. i apples sell for $i, No. 2's might be expected to bring 75 cents, and No. 3*3, 25 cents or thereabouts. Applying these estimates to these various lots of apples, it appears that the actual value of the crop from the treated trees was 2^4 times that from the trees which had not been treated (Column 12). 272 BULLETIN No. 108. [May, 1906.] SPRAYING APPLES FOR THE PLUM-CURCULIO. 273 274 BULLETIN No. 108. [May, To see whether the outer rows of trees were any more likely to be heavily infested by curculios than the inner, — whether curculios entering the orchard from outside would accumulate upon the outer rows, — three trees in the sprayed lot were examined, one from the middle and one from each end of the row farthest removed from the check. No differences in amount of curculio injury were found in these trees, as compared with the average for the plot in general, with the exception of one of the three, which stood at a corner of the orchard next a fringe of forest trees and brush. The fruit of this tree, notwithstanding the four thorough sprayings with arsenate of lead which it had received, had been injured by curculios to the amount of nearly 87 per cent., showing an extensive immigration into the orchard from the adjoining woodland. As this contained both hawthorn and wild cherry-trees it doubtless furnished a con- stant breeding ground for curculios. Foreseeing difficulties of this kind, and also the probability of a mutual influence of check and experimental plots, the precaution had been taken to select, quite early in the season, for comparison, four trees from the center of each plot, and it is thus quite certain that no outside interference or intermingling of effects influenced the contrast obtained in this experiment. Orchard 2 (Plots II. and III.}. — We turn next to the second or- chard (Sections 2, 3, 6, and 7), one half of which was sprayed six times in succession, the other half being left as a check. As a part of these apples were of an early variety (Benoni), and a part were of a late variety (Ben Davis), I will give the results for these two varieties separately. Thirty-two Benoni trees (Plot II.) were sprayed six times in this experiment, in comparison with 34 Benoni trees left as a check, and the apples borne by 3 trees from each of these two lots were picked, measured, counted, and examined July 26 to 29 (Section 2, Columns I to 5), the two sets of trees having been so selected as to make the check lot the nearest possible duplicate of those which had been sprayed. The 3 trees not sprayed yielded 11.4 bushels of apples, and those which had been sprayed yielded 16 bushels (Col- umn 4) — an increase of 40 per cent, in the bulk of the yield as a consequence of the spraying. The 3 trees which had not been treated bore 2,593 apples, while the 3 treated trees bore 3,782 (Column 5) — a difference of 47 per cent, in favor of the treated trees. That is, the sprayed trees bore nearly half as many apples again as those whicli had not been sprayed. The average size of the apples was approximately the same for both lots — 228 per bushel for the un- treated trees, and 236 for the treated. 1906.] SPRAYING APPLES FOR THE PLUM-CURCULIO. 275 Turning next to the ratios of curculio injury to these Benoni apples (Column 6), we find that 21.4 per cent, of the fruit of the un- sprayed trees had been injured by curculios, and 10.3 per cent, of that on the sprayed trees, 48 per cent, of the apples which would have been injured having been protected from injury by the arsenical spray. These Benoni apples were harvested in July, but were not graded into market classes. I consequently have no data as to the total money benefit of the spraying shown by this Plot II. On the other part of this orchard (Plot III.), sprayed six times ( Sections 3 and 7) , were 20 Ben Davis trees which are to be compared with an equal number of this variety left unsprayed as a check. From each of these lots again 3 trees were taken for critical com- parison of the product of those sprayed with that of those unsprayed (Section 3, Columns i, 2, and 3). The final count on all these trees was made September 17. The 3 trees not sprayed gave 16%. bushels of apples, while the 3 trees sprayed yielded 22 bushels (Column 4) — an increase of 34 per cent, in quantity of apples as a consequence of the spraying. The 3 Ben Davis trees which had not been treated bore 2,770 apples, while the 3 treated trees gave 3,063 (Column 5) — a difference of only n per cent, in favor of the treated trees. The unsprayed apples on these trees ran. i/o^to the bushel, and the sprayed apples, 139 to the bushel — a difference of 24 per cent, in size of fruit in favor of the trees which had been sprayed. With respect to the curculio injury to these Ben Davis apples we find that 95.6 per cent, of the unsprayed fruit had been injured by curculios, and 30.7 per cent, of that sprayed ; or, in other words, that 68 per cent, of the apples which would have been injured had been protected from injury by the treatment received. Looking now to the quality of the fruit from these Ben Davis trees, which had been sprayed six times in all (Section 7, Columns 9. 10, and n), we find that the 3 unsprayed trees examined gave a yield of % of a bushel of No. I apples, while the 3 sprayed trees yielded 12.06 bushels; that the unsprayed trees gave 3^4 bushels of No. 2's, the sprayed trees 3 *4 bushels ; that the unsprayed trees yielded ii^j bushels of No. 3's, and the sprayed trees 62/$ bushels. (See Plates III. and IV.) Reducing these quantities to comparable money values by the prices already assigned, we find that the actual value of the crop from the treated trees was 2l/2 times that from the trees which had not been treated. Orchard 3 (Plot IV.}. — In the third and last orchard on which I have to report, the check and the experimental sections do not cor- respond closely, the sprayed trees being all Winesap and Ben Davis, late varieties only, and the check lot almost entirely of early vari- 276 BULLETIN No. 108. [May, 1906,] SPRAYING APPLES FOR THE PLUM-CURCULIO. 277 278 BULLETIN No. 108. [May, eties. As the early varieties were harvested July 15, they were less exposed to injury than the fruit on the sprayed trees, which was harvested from September 16 to 20. This is a difference, however, which tends to diminish the contrast between the sprayed and un- sprayed trees, and thus to show, if anything, a smaller result from spraying than was actually obtained. The Winesap and Ben Davis trees, 119 in number, were sprayed eight times in succession, and the fruit from 4 of these trees (3 Ben Davis and I Winesap) was picked and examined with reference to curculio injuries. The unsprayed orchard used as a check on this experiment contained 145 trees, all Sops of Wine and other early varieties except 4 Ben Davis (see Section 4, Columns i, 2, and 3). The fruit from 9 of these check trees was examined July 15, all Sops of Wine except i Ben Davis. These yielded 3,463 apples, making 14% bushels, equal to 1,540 apples, or 6.44 bushels from 4 trees (Columns 4 and 5), while the 4 trees sprayed, the apples from which were picked September 16 to 20, yielded 3,198 apples, making 24^/2 bushels. These differences in number of apples and bulk of yield can not properly be taken into account in this case, because both might well be attributable, at least in part, to the difference in variety between the sprayed and the check trees from which the fruit was counted. The curculio injuries on the 9 unsprayed trees had affected an average of 91 per cent, of the apples (Column 6), and on the 4 sprayed trees, an average of 18^ per cent., from which it appears (Section 8, Column 7) that 80 per cent, of the apples which might have been injured by curculios if no treatment had been applied, had been saved from such injury by the arsenical spray. Here again it is possible that a varietal difference in susceptibility to curculio injury may have affected these percentages. COST OF THE OPERATION. The reader will be especially interested to know the cost of our operation, figured in terms practical to the fruit grower. I have worked this out in full detail for the 292 trees sprayed in these or- chards, including the actual price of materials purchased in the ordi- nary markets, the amount of materials used, and the labor of applica- tion at $1.25 a day and board for men employed, and $2.50 a day and feed for a team. Without entering into details, unnecessary for my purpose, I find that the total cost ranges from 4 to 5 cents per tree for each treatment, or 17 cents per tree for the four treatments found most effective. Of this only 2 cents was for materials, the remaining 1 5 cents being for labor of man and beast, much of which, in many cases, the fruit grower might supply without special outlay. 1906.] SPRAYING APPLES FOR THE PLUM-CURCULIO. 279 SUMMARY OF SPRAYING RESULTS. Finally, to sum up in a word the most important practical results of the orchard experiment with arsenate of lead, we may say that four sprayings of apple-trees of late varieties, exposed to a very heavy attack by the plum-curculio, the first spraying applied in early May just as the trees are coming into bloom, and the others at in- tervals of 10 days thereafter, the whole operation costing 17 cents per tree, may be expected to increase the yield of the orchard about one half, to increr.se the average size of the fruit by about a fifth, and so to improve the quality of the apples that they should be worth from 2^2 to 3 times as much as if the orchard had not been sprayed. POISON TESTS OF SPRAYED APPLES. The arsenate of lead used in experiments described in this paper is an unusually adhesive insecticide, remaining upon trees in visible quantity weeks and even months after it has been applied. Evident traces of the mixture were still visible in October on leaves which had fallen from trees sprayed with the arsenate of lead July 4. In view of this fact it seemed to me important that experiments should be made to determine the amount of poison carried by apples treated with this insecticide within a reasonable limit of time after the spray was applied. I consequently directed, in 1905, the spraying of apple- trees with various arsenical compounds, and among others with the home-made arsenate of lead, and obtained analyses of the peelings of apples so sprayed taken from 2 trees within a day of the applica- tion of the insecticide, and from a third tree 2 months thereafter. The first of these trees, of the Duchess variety, received 2 spray- ings with the arsenate of lead — the first June 9 and the second July 4 — not having been previously sprayed at all that year. In both these sprayings the insecticide was used at 4 times the common strength — 12^2 ounces of acetate of lead and 5 ounces of arsenate of soda to i2l/2 gallons of water instead of the usual 50 gallons. The next day, July 5, six apples, averaging two and a fourth inches in diameter, were carefully picked from this tree by the stem and peeled at once, the apple being held upon the point of one knife while it was peeled with another, to avoid removing any part of the poison unnecessarily. The peelings were then dropped into a dry, clean, new Mason jar and submitted for chemical analysis to Dr. Wm. M. Dehn, of the Chemical Department of the University of Illinois. It should be said that the weather in the interval between spraying and collection of the apples had been dry. According to Dr. Dehn's 280 BULLETIN No. 108. [May, report, these apple peelings thus collected yielded 36.6 parts per mil- lion of arsenious acid, enough to equal .2562 grains of arsenic to an avoirdupois pound of the sample peelings. This would mean that one would have to eat approximately four pounds of apple peelings to get a grain of arsenic if the fruit were taken the day after spray- ing from a tree which had received four times the usual strength of this insecticide. Another tree, a Benoni, differed especially in two respects from the foregoing. It had been sprayed three times by the owner earlier in the season, and it was sprayed twice by us — June 9 and July 4 — but with arsenate of lead in the strength usual in practical orchard work, that is, i2l/2 ounces of acetate of lead and 5 ounces of arsenate of soda to 50 gallons of water. The earlier sprayings were as fol- lows : First spraying about April 3, before the appearance of the bloom, with 3 pounds copper sulphate, 5 to 6 pounds lime, 2 ounces arsenate of soda, and 2 ounces Paris green, to 50 gallons of water ; second spraying about April 26, just after the bloom had fallen, with 2 pounds copper sulphate, i pound Lorenberg's arsenate of lead, 2 ounces Paris green, 3 to 4 pounds lime, and 50 gallons of water. Rain fell more or less for three days after this second spray- ing. The third spraying, about May 3, was with 2 pounds copper sulphate, 3 to 4 pounds lime, i pound Lorenberg's arsenate of lead, 2 ounces Paris green, and 50 gallons of water. From this tree six apples averaging two inches in diameter were picked July 5, the day after our own second spraying, with the precautions described above. The peelings tested by Dr. Dehn yielded 32.9 parts of arsenious acid per million, equivalent to .2303 grains of arsenic per pound of the samples. It will be noticed that, although the insecticide here used con- tained only one fourth as much of the arsenate as that applied to the Duchess tree, the percentage of arsenic remaining on the fruit was nearly as large. The third tree treated was a Rome Beauty, sprayed, like the preceding, three times, April 3, April 26, and May 3, approximately, with combinations of Bordeaux mixture and arsenical insecticides, and further sprayed, June 9 and July 4, with home-made arsenate of lead at the rate of 12^ — 5 — 12^2 ; that is, like the first tree, with four times the usual strength. The apples were picked from this tree September 4, two full months from the time of spraying. Those chosen showed more than the aver- age amount of residue of the insecticide on the fruit. They were picked into baskets, poured into a box where they were packed closely by hand, and shipped to the office at Urbana, being given average woe.] SPRAYING APPLES FOR THE PLUM-CURCULIO. 281 shipping treatment. Ten apples were later taken from the box and carefully peeled, the peelings being submitted, as before, to Dr. Dehn for examination. Notwithstanding the long exposure in the or- chard, the report on the arsenical contents of this material is very similar to that of the preceding determinations.