June, 1933 (161 (175 (18) (19) (20)
INDUSTRIAL AND ENGINEERING CHEMISTRY
Onn. E. R. de. TND. ESG.CHEX..22.836 (1930). Roa& R. C.,’U. S. Dept. Agr., Misc. Pub. 120 (1932).
R. C., Ibid., Yearbook, pp. 177-9, 1927. C., U. 5. Patent 1,524.884 (Feb. 3, 1925). Shafer, G. D., hIich. Agr. Expt. Sta., Tech. Bull. 11 (19111, Roark,
Roark, R.
21 (1915).
633
(21) S m u t h , H . F., IND. EXG.CHEM..24, 229 (1932). (23) Wileoxon, Frank, and Harteell, Albert, Contrib. Boyce Thompson Inst., 3, 1-13 (1931). (23) Woodruff, “Foundations of Biology,” Maemillan, 193 1.
RECEIVED March 29,
1933.
Selenium Insecticide Ma-terial for Controlling Red Spider (2.B. GNADINGER,McLaiighlin Gormley King Company, Minneapolis, Minn.
T
plant bugs, leaf rollers, and many HE v a r i o u s species of A new selenium insecticide f o r the control of mites, c o m m o n l y r e various speciesof red spider is described. The others. This fact has also been confirmed by Richardson ( 7 ) . to red spiders’ results so f a r obtained with this material are xicotinel veratrine, cresol, and are widely d i s t r i b u t e d a n d cause great damage to a large promising but further work must be done, emmany other contact insecticides variety of plants. The comploying it on a commercial scale over a period of are useless against red spiders a t several years. Experimental work of this kind concentrations commonly e m mon or greenhouse red spider, is now in progress on ,.itrus and deciduousfruits ployed to control other pests. Tetranychus telarius Linn., is known to feed on nearly two Fumigation with hydrocyanic hundred kinds of plants, and it and the effect Of this Of On the acid will not control citrus red has been estimated that the loss different citrus scales is also being incestigated. mider. The most satisfactory control it causes to the cotton crop alone may reach a total of $2,000,000 in a single year (3). heretofore has been obtained with oil sprays. Unfortunately, It is found in greenhouses throughout the Cnited States concentrations of oil that will control the greenhouse spider and has caused serious injury to small fruits and deciduous will also frequently damage tender greenhouse plants. Oil fruits. It is said to have caused nearly as much damage sprays also remove the silvery “bloom” from the leaves of to the 1931 apple crop, in the State of Washington, as the carnations and blue spruce, and from the fruit of grapes codling moth. The so-called two-spotted mite, Tetranychus and prunes, thus reducing their commercial value. Oils are bimaculatus Harvey, is held by some authorities to be the much less effective against the web-spinning species of spiders because they do not readily penetrate the webs. same as the common red spider. Another species, which like T . telarius Linn. spins a heavy Oil has been used extensively for the control of citrus web, is the Pacific mite, Tetranychus pacificzis MeGregor. red spider. Woglum, La Follette, Landon, and Lewis (11), This has caused enormous damage to the vineyards of however, find that: California and to certain deciduous fruits. The European The use of oil sprays on citrus trees is associated with conred mite, Paratetranychus pilosus Can. and Fanz., is an siderable hazard. Perhaps the most outstanding ill effect, important pest in the Pacific Northwest, attacking most more or less experienced in sprayed orchards, is reduction of deciduous fruit trees (6); the citrus red spider, Paratetrany- fruit quality. Increased dead wood is also a source of much chus citri ItlcG., is one of the most important citrus pests (11). complaint, especially on oranges in the interior areas. Injury to foliage is almost entirely absent and fruit burn exceptional. It closely resembles the European red mite, and some ento- Fruit drop may occur, especially when the fruit is small. Overmologists consider the two identical. The clover or brown spraying, dry soil, extreme weather, or too heavy oil accentuate mite, Bryobia praetiosa Koch., is a common pest of fruit drop. In the case of lemons, oil sprays may influence coloration, trees (6). A number of other species of less economic im- also produce excessive drop of tree ripes. The use of oil sprays on oranges in late autumn or early winter, especially the medium portance than the foregoing is also shown. t o heavy, tends t o produce reduced blossoming and crop the Red spiders feed by thrusting the lancelike mouth parts next season, also is likely to affect quality through interfering into the leaf and extracting the plant juices and chlorophyll. with proper coloration, influencing the texture and internal The leaves become browned or bronzed, and, if the infesta- quality. Analyses have shown in both the case of Valencias and navels that oil sprays tend to reduce the acidity and soluble tion is not checked, there is more or less defoliation. In solids, frequently leading to a weakening of the juice and detriheavy infestations of the spinning species, the foliage and ment t o flavor. flowers are covered with webs. Annual plants rnay be killed outright or so stunted that the crop has no commercial It is generally admitted that oil cannot be applied to citrus value. Deciduous trees are frequently so severely injured trees a t certain seasons of the year, nor when high temperathat little or no crop is obtained the following year because tures are accompanied by low humidity, although heavy the formation of fruit buds is prevented. The foliage of infestations of spiders may be present. citrus trees becomes yellowed and the peel of the fruit harCommercial lime-sulfur has been used to control red spider dens; there is considerable leaf drop, resulting in dead twigs on hops and on citrus. It gives fair control of spiders, but and branches, does not kill the eggs and hence is of only temporary value. Its effectiveness may be greatly reduced by weather condiPRESEKT METHODS OF CONTROL tions. Since the spiders do not chew the foliage, they are little Sulfur dust, like lime-sulfur, will control the spiders but affected by stomach poisons, and control must be obtained has little or no effect on their eggs; hence several applicaby contact insecticides. The red spiders are peculiarly tions are necessary for good control. Moreover, sulfur is immune to the powerful contact insecticides, pyrethrum ineffective if the temperature is less than 80” F. (26.7’ C.) and rotenone, which readily kill such resistant insects as and may injure the plant if the temperature is more than Japanese beetles, potato beetles, cockroaches, tarnished 100’ F. (37.8” (2.). Potassium sulfide has been used for
INDUSTRIAL AND ENGINEERING CHEMISTRY
634
red spider control on cotton (S), but the concentration recommended is too high for greenhouse plants. USE OF SELENIUM FOR RED SPIDERCONTROL The writer made several hundred tests on red spiders with sulfides of ammonia, sodium, and potassium, with and without added sulfur. Among the sulfides investigated were sodium and potassium hydrosulfides and the sulfide of ammonia formed by saturating ammonium hydroxide with hydrogen sulfide. Some experiments were made with monosulfides (potassium, sodium, etc.) and the polysulfides prepared by the reaction of alkali hydroxide solutions with sulfur. Solutions of the polysulfides were also made by dissolving varying amounts of sulfur in solutions of the monosulfides. The hydrosulfides were not sufficiently toxic to spiders or eggs. The monosulfides were more toxic, but were too caustic for use on greenhouse plants. The polysulfides were also quite toxic to spiders but, a t the required concentration, caused serious injury to the plants. Several of the sulfides tested appeared to be quite promising at first, but further experiments in every case brought to light objectionable features which made the product unsatisfactory for commercial use; for example, a polysulfide formed by dissolving sulfur in potassium ammonium sulfide solution was well tolerated by most plants and killed adult spiders, but was not sufficiently toxic to the eggs. Several months were spent in working with this compound in the hope that some modification might increase its toxicity. Finally, as a last resort, the polysulfide sulfur was replaced by selenium, resulting in a marked increase in toxicity both to spiders and eggs. The element selenium is closely related to sulfur chemically and forms analogous compounds. Selenium dissolves in solutions of the alkali hydroxides forming complex selenides. The nature of these compounds appears to depend largely on the concentration of the solution. Selenium is also soluble in boiling barium hydroxide solution, but, on cooling, most of the barium selenide is deposited.
Vol. 25, No. 6
different selenium compounds,l that best suited for greenhouse plants was found to be selenium dissolved in potassium ammonium sulfide solution, in proportions corresponding to the formula (KNH8)SSe. A 30 per cent solution of this material was designated Selocide and was submitted to a large number of tests against different mites. Compounds of tellurium were tried, but they were not as toxic, as stable, or as easily prepared as those of selenium. LABORATORY AND
GREEXHOUSE SPRAYING EXPERIMENTS
Selocide was subjected both to laboratory and commercial tests on greenhouse plants. The 30 per cent solution was diluted with 100 to 400 parts of water, and 0.2 to 0.4 gram of high-grade soap flakes per 100 cc. of spray solution was used as spreader. The laboratory tests are described in Table I. TABLEI.
LABORATORY TESTSWITH SELOCIDE SPIDER(2'. telarius L.)
PLANT DILCTION INFESTED SOAP KILL Gram/100 cc.
Gladiolus Gladiolus Aster Aster Gladiolus Aster Aster Carnation Aster Gladiolus 1:lOO Gladiolus 1 : 100 1:lOO 1:lOO 1:lOO 1 : 100 1 :200 1:200 1:200 1 : 200 1:200
0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
% 99 100 99 97 99 99 93 83 90 85 97
AGAINST
RED
PLANT DILUTION INB~STEDSOAP KILL 1 : 100 1 : 100 1:200 1:200 1:200 1:200 1 :300 1 :300 1 :400 1 :400 1:200
Aster Gladiolus Aster Mum Carnation Gladjolus Gladiolus Aster Gladiolus Aster Gladiolus
G 100 a mcc. /0.2 0.2 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4
?& ._ 98 99 95 94 88 90 30 80 15 60 86
Some of the tests reported in Table I were made on spiders raised in the laboratory. Others were on spiders, obtained from different greenhouses, which were sprayed in the laboratory within a few minutes after collecting the plants. All laboratory tests were made with a compressed-air sprayer with a uniform pressure of 12.5 pounds per square inch (0.88 kg. per sq. cm.). The kill was calculated 24 hours after spraying by actual count under the binocular. The average number of spiders per test was 576.
TESTSWITH SELOCIDE AGAINST REDSPIDER(2'. telarius L.) TABLE 11. COMMERCIAL DILUTION PLANT
SOAP
REMARKS
KILL
%
1:128
Carnation
Gram/lOO cc. 0.2
1 :200
Carnation
0.4
95
1:200
Carnation
0.4
90-95
1 :200
Carnation
0.4
..
1 :200
Aster
0.4
98
1:200
Buddleia
0.4
95
99
Bench-sprayed 10/8. Observed at intervals of 3 or 4 days until 12/1; few spiders could be found although lants were badly infested when sprayed Sprayed 1 O A 3 at noon, s ringed with water at 5 P. M . Observed until 12/1, when only a few spiders were found in 1/2 bencg. No injury to plants; did not remove the "blqom" from leaves Bench-sprayed 10/14; badly infested. Observed 10/21; few young spiders and large number of unhatched eggs . Same bench as preceding experiment sprayed again 10/21. Observed l0/31; very few spiders on whole bench. Observed lZ/l; very few spiders; plants in excellent conditlon Two badly infested benches, upper parts of plants covered with webs. Sprayed 10/15; observed 10/16, practically no live spiders could be found. 10/26 only a few adult spiders could be found; a few r u n g spiders present and large number of unhatched eggs. Plants covered with flowers, color right, and foliage much better Entire bench moderately infested, sprayed 10/22. Very few live spiders 10/31. Very slight burn t o few of tenderer shoots. 12/1 ilants in excellent condition; very few spiders
Selenium is almost insoluble in solutions of hydrosulfides but dissolves readily in solutions of the monosulfides. It is soluble, but to a less extent, in solutions of the polysulfidesfor example, in calcium polysulfide or commercial lime-sulfur . The stability of the selenides varies considerably. If a concentrated solution of a monosulfide containing dissolved selenium is diluted with water, most of the selenium will precipitate immediately as red selenium if the ratio of selenium to monosulfide is high. If a low proportion of selenium is used, however, no precipitation will occur for several hours or even days. The selenides all appear to be much more toxic to red spiders than the corresponding sulfides. Moreover, their action is quite specific, since other insects-leaf hoppers and leaf rollers, for example-are not greatly affected by the selenium compounds. After a large number of tests with
The commercial sprayings, which were made with a pressure sprayer generating 180 to 200 pounds per square inch (12.7 to 14 kg. per sq. cm.) at the nozzle, are described in Table 11. The excellent control obtained in these commercial tests and the absence of spiders even after a considerable interval indicated that the eggs were killed as well as the spiders. Tests were conducted in a commercial greenhouse to determine the effect of Selocide on plants. After spraying, the plants were kept under commercial conditions normal for the particular plant. The results of these experiments are given in Table 111. From Tables I, 11, and I11 it is apparent that Selocide at a dilution of 1:200 with 0.4 gram of soap.per 100 cc. can be 1 Patents are pending covering the use of these selenium compounds as insecticides.
June, 1933
IXDUSTRIAL AND ENGINEERING CHEMISTRY
635
the spray as well as was expected. This was rather surprising in view of the fact that delicate greenhouse plants were not injured by the 1:200 dilution, and it was surmised that the injury to fruit trees was due to the effect of sunlight on the spray residue. About the same time Lamiman (3) working with Selocide on Pacific red spider infesting California vineyards, discovered that it could be used successTABLE111. EFFECTOF SELOCIDE ON GREENHOUSE PLANTS fully outdoors a t dilutions which the writer had found entirely ineffective in the greenhouse. Using a dilution of EFFECT ON PLANT PLANT SPRAYED DILUTION S O A P 1:800, Lamiman obtained kills of 95 to 100 per cent on Gram/100 cc. spiders and eggs. Whether this difference in behavior is 1:50 N o burn 0.20 Calceolaria due entirely to the action of sunlight or in part to the higher 0.20 No burn 1:dO Rex begonia 0.20 1:50 No burn Primrose pressures used in orchard and vineyard spraying has not been 0.20 N o burn Snapdragon seedling 1 : 5 0 No 0.20 1:50 . burn Carnation determined. 0.20 1:50 Burned young frands Holly fern Burned young leaves 1:5O 0.20 In the fall of 1932 California citrus growers suffered an Cineraria 1:50 0.20 Burned young fonds Boston fern exceptionally heavy infestation of citrus red spider. This No burn 1:lOO 0.20 Calceolaria No burn 1:lOO 0.20 Rex begonia afforded an opportunity for determining the value of Selocide 1: 100 0.20 No burn Primrose 0.20 No burn a t higher dilution against this mite. The writer conducted a Snapdragon seedling 1:lOO 1:lOO 0 . 2 0 to young fronds Very slight burn Holly fern number of experiments with Selocide on P. citri McG. in1:lOO 0.20 Very slight burn t o young fronds Boston fern 1:lOO 0.20 Very slight burn to young leaves Cineraria festing both lemons and oranges. The Selocide sprays were N o burn 1 : 100 0.20 Buddleia N o burn 1:lOO 0.20 Melior begonia tried a t such dilutions and in such combinations that the 1:lOO 0.20 No burn Carnation cost of spray material did not exceed $2.25 per 300-gallon 1 : 100 0.20 No burn Sweet pea 0.20 1:lOO N o burn Violet tank. It was generally agreed that this cost is satisfactory 0.20 1:lOO No burn Forget-me-not 0.20 1: 100 No burn for an efficient citrus spider spray. Selocide was tried with Cyclamen 0.20 1:128 No burn Carnation different spreaders and in combination with oil and with 0.20 1:128 Slight burn to tender shoots Buddleia 0.20 1:128 No burn Rose lime-sulfur. Dilutions of 1:500 and 1:600 were employed No burn 0.20 1: 128 Chrysanthemum 1 : 200 N o burn 0.20 Sweet pea instead of the 1:200 dilution previously used in greenhouse 1 : 200 Very slight burn, not important 0.20 Buddleia work. commercially 0.40 Very slight burn, not important Buddleia 1:200 Heavy infestations of citrus mite were located in three commercially No burn 1:200 0.40 . .-.~ Calla groves, and twenty-eight to thirty trees in each grove were 1:200 0.40 No burn Stevia blocked off for the experiments. From five to nine different 0.40 1:200 No burn to foliage or buds; open Aster flowers burned sprays were applied in each grove, using three to five trees 0.40 N o burn Holly fern 1: 200 No burn t o foliage very very Cyclamen 1 : 200 0.40 for each spray. The trees employed for each spray were sliaht burn to f l o w k selected a t random, and precautions were taken to prevent Calceolaria 1:200 0.40 N o 5urn 0.40 Cineraria 1:200 Bad burn reinfestation from the rest of the grove. Where necessary a 0.40 Rex begonia 1:200 No burn 0.40 No burn Snapdragon seedling 1 : 200 canvas screen was used to prevent spray material being blown 0.40 N o burn Rose 1:200 on the wrong tree. 0.40 No burn Sweet pea 1:200 0.40 N o burn (tenders leaves slightly) Rose 1:200 Before spraying, the degree of infestation was determined 0.40 No burn Violet 1:200 by counting the spiders on nine to twenty-one trees in each grove. The counts were made, in the field, on ten to twenty OUTDOORSPRAYINQ EXPERIMEKTS leaves from each tree, taken from all sides, a t a height of I n the spring of 1932 the writer conducted a number of 4 to 8 feet from the ground. The trees were then sprayed preliminary experiments with Selocide on other mites. The and tagged, and four counts were made a t intervals to deter30 per cent solution was diluted with 200 parts of water, mine the effect of the spray material. Similar counts were and 0.4 gram of soap per 100 cc. of spray was used as spreader. also made on control trees, which were not sprayed. All Commercial tank sprayers were used generating from 300 counts were expressed as the average number of eggs or to 500 pounds per square inch (21 to 35.2 kg. per sq. cm.) spiders per leaf. pressure. The citrus mite, brown mite, and certain rust The first experiments were made a t the Murphy Oil Commites were all as readily controlled with Selocide as T. pany Ranch, Whittier, Calif., through the courtesy of C. L. telarius. Holmes, in charge of pest control. The block of trees reTests for tolerance were also made on orange, almond, served for this test had been sprayed with oil 6 months apple, peach, prune, damson, apricot, and pear foliage and earlier. The rest of the grove had been oil-sprayed recently. fruit. In some cases lead arsenate was applied before or The average infestation per leaf in the reserved block was after the Selocide. In general the stone fruits did not tolerate 47.7 eggs and 10.2 spiders, which is considered heavy. The
used to control red spiders (T.telarius L.) without injury to tender greenhouse plants. It was found that good control could also be obtained by syringing 1 to 2 hours after spraying with even less danger of burning. I n the tests on sweet peas and roses it was noted that Selocide had considerable fungicidal value, giving excellent control of mildew.
~
~
TABLEIV. EFFECTOF SELOCIDE ON CITRUSMITE INFESTING LEMONTREES,WHITTIER,CALIF. INFEOTATIOXa
BEFORE
SPRAY COMPOSITION I Selocide 1:600. liquid soap 1.600 2 Selocide 1:60d; liquid s o a p 1:600; trisodium hosphate 4 O B . per 100 gal. 3 Serocide 1:600: liauid s o m 1:600: trisodium hosphate 8 01.per 100 gal. 4 Serocide 1:500. blood albumin 4 oz. per 100 gal. 5 Selocide 1:500! blood albumin S oz er 100 gal. 6 Selocide 1:SOO': oil 1:300; blood algumin 4 OB. er 100 gal 7 Sefocide 1:500. lime-sulfur 1 :300 8 Selocide 1:600! paste flour 16 02. per 100 gal. 9 Selocide 1 : 6 0 4 paste flour 8 oz. per 100 gal.; blood albumin 4 OB. per 100 gal. 10 Controls, not sprayed Average number per leaf. '
TREE :a 3 3
SPRAYINQ
11/13/32 Spiders 30.5 4.4 45.4 9.0
Eggs
11/16/32 Spiders 34.6 2.0 3.4 37.8
Eggs
INFESTATION" AFTER SPRAYINQ 11/19/32 Spiders 4.1 1.8
Eggs
15.9 20.1
11/24/32 Eggs Spiders 8.0 1.2 9.1 1.6
12/3/32 Eggs Spiders 3.3 0.6 5.8 1.1
3
43.3
14.1
42.9
1.6
25.3
3.7
20.0
3.0
6.1
1.3
3 3 3
23.3 59.9 84.8
7.5 11.8 13.0
17.2 30.1 52.7
1.6 0.3 0.0
11.3 17.6 47.7
2.6 4.1 0.0
11.2 7.9 28.1
1.9 4.1 0.0
1.8 3.1 2.3
1.6 3.6 0.0
3 3 3
41.5 68.7 24.7
11.8 12.4 5.7
32.5 52.6 19.4
0.2 1.4 0.4
23.3 41.7 22.1
0.0
1.6 1.5
13.5 10.7 6.2
0.1 2.5 2.1
3.1 4.2 1.9
0.0 1.5 1.3
3
54.3
12.0
9S.9
11.5
80.9
20.8
41.6
8.6
19.8
8.7
636
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY TABLE
v.
EFFECTO F SELEXIUM SPRAYS
ON
P.
Vol. 25, N o . 6
INFESTING NAVELORANGE TREES,RIVERA,CALIF.
&Ti
INFESTATION' BEFORE SPRAYINQ
SPRAY
11/15/32
COMPOSITION
TREES Eggs
I-L Selocide 1:600. liquid soap 1:600 Selocide 1:600! liquidsoap 1:600; trisodium phosphate 8'02. per 100 gal: 4-L Seocide 1:500; blood albumin 4 01. per 100 gal: 5-L Selocide 1:500; blood albumin 8 02. per 100 gal. 6-L Selocide 1:600; oil 1:300; blood albumin 4 02. per 100 gal. 11-L Lime-sulfur saturated with selenium 1:533: blood albumin 4 01. per 100 gal. 10-L Controls, not sprayed a Average number per leaf. 2-L
.
TABLEVI. EFFECTOF
gal. Lime-sulfur 1:300; blood albumin 4 per 100 gal. 10-H Controls, not sprayed a Average number per leaf.
11/18 32
Eggs
kpiders
11/26/32
7
12/4/32
Eggs
Spiders
Eggs
Spidere
11.3 9.6
2.5 1.1
3.7 2.5
2.8 0.9
20.9 3.6
27.7 13.0
3.5 1.3
8.0 10.3
2.7 1.5
3
41.6
11.3
20.0
0.7
11.0
1.7
9.1
1.6
2.8
1.6
3
24.5
10.8
16.4
0.3
16.2
1.7
13.9
1.8
2.1
4.0
4
45.2
27.8
57.1
0.0
33.0
0.0
30.9
0.0
2.0
0.1
4
55.7
19.0
40.2
0.2
34.9
0.2
21.4
1.8
8.5
2.4
4
28.5
14.8
29.6
10.2
32.3
12.4
22.0
13.9
10.9
5.3
P.
C h i
INFESTING NAVEL OR.4NGE TREES,PASADES.4, CALIF. INFESTATION" AFTER SPRAYING
BEFORE S P R A Y I N Q
02.
kpidera
47.4 21.5
INFESTATION" 11/23 32 TREES EEKS koiders -5 45.5 15.3 4 4
11/21 32
Eggs
3 3
VARIOUS SPRAYS ON
SPRAY COMPOSITION 6-H Selocide 1 :600; oil 1 :300; blood albumin 4 02. per 100 gal. 7-H Selocide 1:500. lime-sulfur 1:300 11-H Lime-sulfur said. with selenium, 1 :500; blood albumin 4 02. per 100 gal. 12-H Oil 1:300; blood albumin 4 02. per 100 13-H
INFEBTATION" AFTER SPRAYING
7
Spiders
11/25 32
Eggs
11/28 32
12/5/32
Eggs
kpiders
Eggs
Spiders
7
12/8/32
23.4
kpiders 0.00
Eggs
Spiders
26.2
0.00
5.8
0.10
3.6
0.08
41.6 32.1
14.3 12.8
16.9 38.3
0.03 0.40
11.4 16.4
0.06 0.50
3.6 6.1
0.40 0.80
2.7 7.7
0.20 1.40 0.50
4
46.2
26.4
47.6
2.60
26.5
1.30
12.9
1.0
14.3
4
36.7
12.9
18.3
1.50
14.1
2.60
8.0
3.10
4.5
2.60
6
48.7
12.6
40.1
16.00
37.4
12.80
32.7
13.60
18.8
8.50
solutions were applied with a sprayer a t a pressure of 450 pounds per square inch (31.6 kg. per sq. cm.). The experiments are described in Table IV. One of the primary objects of these experiments was to determine the spreader best suited for use with Selocide. In experiment 1 a 40 per cent coconut oil-potash liquid soap was used. The water a t Whittier was very hard; consequently, in experiments 2 and 3 it was first softened with trisodium phosphate. Although the infestation was greatly reduced, none of these three sprays was considered satisfactory. Much better control is necessary with citrus than with deciduous trees because the infestation will build up on citrus in the course of a year, unless nearly 100 per cent kill is obtained. With deciduous trees 90 per cent kill would be satisfactory because the tree will shed its leaves before the infestation can again become of economic importance. Blood albumin was used as spreader in sprays 4 and 5 . This blood albumin was a powder containing 25 per cent albumin and 75 per cent fuller's earth; it complied with the specifications given by Smith (8). The control in these tests m-as also unsatisfactory. Paste flour and paste flour with blood albumin were tried in sprays 8 and 9 with unsatisfactory results. Selocide with lime-sulfur gave excellent control (spray 7 ) . The lime-sulfur was a commercial brand, containing about 28 per cent calcium polysulfide and 3 per cent calcium thiosulfate. Selocide with oil (spray 6) gave complete control. The oil used was a light medium spray oil of 70 viscosity; it was emulsified with blood albumin as recommended by Smith (8),and the Selocide was then added. These experiments showed that a uniform film of Selocide spray, covering the leaf, is unnecessary. The best spreads were obtained with sprays 5, 3, 2, 9, 4, 1, and 8, in order: sprays 6 and 7 beaded considerably but gave the best control. No injury to blossoms, foliage, or fruit was observed in any of the tests. At Rivera, Calif., a block of twenty-eight navel orange trees was reserved in a corner, and the remainder of the grove was sprayed with oil. The average infestation in the reserved block was 30.3 eggs and 14.1 spiders per leaf. Six different sprays were applied, using a pressure of 400 to 450 pounds per square inch (28.1 to 31.6 kg. per sq. cm.). The results are summarized in Table V.
The degree of control obtained with the different sprays described in Table V is about the same as was found in the first series of experiments (Table IV). Spray 6-L (Selocide with oil) gave more than 99 per cent kill, but the other solutions did not give satisfactory control. Spray 11-L was a commercial lime-sulfur solution saturated with selenium. During the last week of the experiment there was a marked decrease in the infestation of the controls, due to natural causes. The materials which had shown most promise in the preceding experiments were now subjected to a third test. Through the courtesy of H. C. Chaplin, of the Sierra MadreLamanda Citrus Association, arrangements were made to spray an isolated block of 39 navel orange and 90 lemon trees near Pasadena. The orange trees were in poor condition, largely because of the heavy spider infestation which averaged 42.6 eggs and 16.2 spiders per leaf. The lemons had been fumigated for red scale with hydrocyanic acid but were still heavily infested with spiders. The lemons were sprayed only with Selocide-oil solution 6-H. The experiments are described in Table VI. As in the previous tests the Selocide-oil spray gave the best control, with the Selocide and lime-sulfur spray second in efficiency. Lime-sulfur saturated with selenium did not give a satisfactory kill. Oil alone (12-H) and lime-sulfur (13-H) without Selocide did not give control when applied a t the concentrations used with Selocide in experiments 6-H and 7-H. This was anticipated because it is generally recognized that 1.5 per cent light medium oil or 2 per cent lime-sulfur are the minimum amounts necessary to control P. citri ( 2 , 10, 11). It is believed that the Selocide-oil spray containing only one-third per cent light medium oil can be applied a t any time without injury to the trees. A small orange tree examined several months after being sprayed with 1:50 solution of Selocide showed no injury. The control obtained on the lemon trees sprayed with solution 6-H was nearly as good as on the oranges. The lemons were sprayed, commercially; consequently, coverage was not so good as in the test sprayings. Sixteen days after spraying, the average number of spiders per leaf was 0.14. In addition to the information given in Tables IV to VI, data were collected regarding the ratio of newly hatched larvae t o
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1933
older stages of spiders in the different counts. The Selocideoil spray (6, 6-L, 6-H) killed both eggs and spiders promptly. The average kill for all experiments obtained with this spray was 99.4 per cent. The various lime-sulfur sprays did not destroy the eggs so efficiently, and considerable numbers of newly hatched larvae were apparently killed soon after hatching. The efficiency of such a spray might be greatly influenced by weather conditions. It should be mentioned that only those eggs were counted which were normal in appearance. Most of the sprayed eggs reported in the last column of Tables IV and V were probably dead, although normal in appearance under the low magnification used in counting; otherwise, they would have hatched in the 20to 21-day interval between the time of spraying and the final count. The prevailing humidity and temperature, during the period of the experiments on citrus, are given in Table VII. TABLEVII. PREVAILING HUMIDITY AND TEMPERATURE DURING CITRUSEXPERIMENTS DATE (1932)
Kov. 13 14 15 16 17 _. 18 19 20 21 22 23 24 25 26 27 28 29 30 Dec. 1 2 3 4 5
REL.ATIVE HEMIDITYc Min. Max.
%
%
16 32 14 19 21 23 23 26 32 32 13 15 14 16 44 42 49 4s 31 19 19 21 30
68 75 31 37 43 37 39 49 73 72 20 18 20 72 78 78 78 73 62 35 34 49 78
F. 46 49 60 59 60 63 59 55 48 54 62 62 63 52 51 44 52 46 46 54 58 50 47
Min.
TEMPERATCREMax.
C. 7.8 9.4 15.6 15.0 15.6 17.2 15.0 12.8 8.9 12.2 16.7 16.7 17.2 11.1 10.6 6.7 11.1 7.8 7.8 12.2 14.4 10.0 8.3
F. 83 74 88 83 88 90 87 85 81 78 88 82 85 86 72 73 77 66 69 75 81 83 73
--.
C. 28.3 23.3 31.1 28.3 31.1 32.2 30.6 29.4 27.2 25.6 31.1 27.8 29.4 30.0 22.2 22.8 25.0 18.9 20.6 23.9 27.2 28.3 22.8
TOXICITY OF SELENIUM SPRAYRESIDI-E Selocide, diluted and sprayed on fruit or foliage, leaves a rust-red stain of selenium. The effects of air, moisture, and sunlight on this spray residue are not definitely known. The toxicity of this residue to the consumer of the fruit is also unknown. Czapek and Weil ( 1 ) report that metallic selenium is nonpoisonous. Woodruff and Gies (12),experimenting with dogs, found that 4 grams of finely powdered selenium introduced into the stomach, manifested no toxicity whatever and passed out in the feces. They also found that 4 mg. of soluble selenite or selenate per kg. of body weight, given by mouth, caused death quickly. Solis-Cohen (9) states that the selenides and selenates are converted into selenites in the body and the selenite is then reduced to selenium which is deposited in the tissues. The formation of the insoluble selenium in the blood stream plugs the capillaries of the lungs, and the symptoms of poisoning are clue largely to the resulting mechanical obstruction. The fatal dose of sodium selenite for most mammals is said by Solis-Cohen to be 4 to 6 mg. per kg. of body weight; sodium selenate is about half as toxic as the selenite, and colloidal selenium is somewhat less toxic than either. Kelson, Hurd-Karrer, and Robinson (5) of the Department of Agriculture have studied the action of sodium selenate on wheat. Sodium selenate added to the soil in amounts equivalent to 15 p. p. m. of selenium produced distinct chlorosis and stunting of wheat plants. Morris and Snhgle (4) have observed a similar effect on oat plants grown in Shive’s nutrient solution containing arsenic trioxide equivalent to 5 p. p. m. of arsenic.
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Iielson, Hurd-Karrer, and Robinson also report that wheat plants in soil containing sodium selenate, equivalent to one p. p. m. of selenium, grew and matured normally but the grain and straw from these plants were quite toxic to rats and guinea pigs, causing death in a few weeks. The selenium content of the straw and grain and the dosage of selenium administered to the test animals are not given. Wheat containing 8 to 10 p. p. m. of selenium produced macroscopic changes in the livers of test animals. The selenium in the wheat was found to be associated intimately with the protein, in some undetermined form. These investigators conclude that “Selenium can be assimilated from the soil by a t least some and possibly all plants, and the degree of toxicity of the particular compound used in spraying a plant is not a measure of the toxicity of the compound found in the plant.” It should be noted that the experiments of Nelson, HurdKarrer, and Robinson were made with sodium selenate, and hence their conclusions are not directly applicable to Selocide. Nevertheless, the toxicity of Selocide spray must be further investigated before it can safely be recommended for food crops. Although chemically selenium is closely related to sulfur, most investigators agree that the toxic action of the selenites and selenates is similar to that of the arsenites and arsenates. When Selocide is diluted 1:500, the spray solution contains 0.01 gram of selenium per 100 cc. The solution of arsenate ordinarily used contains 0.05 gram of arsenic per 100 cc. Moreover Selocide would be applied only once or twice a year, whereas arsenic is applied from four to nine times per year. It seems fairly certain therefore that Selocide would be much less dangerous than arsenical sprays even if all of the selenium in the spray residue were oxidized to selenite, which is not the case.
ACKNOWLEDGMENT I n conclusion the writer wishes to express his appreciation for invaluable suggestions and assistance in connection with this work to R. W. Haegele, in charge of Parma Entomological Field Station of the University of Idaho; J. F. Lamiman, Department of Entomology, University of California; Henry Rosacker, Hans Rosacker Floral Company, Minneapolis; and especially to H. H. Wilcomb, Deputy Agricultural Commissioner, Los Angeles County, Calif. Acknowledgment is also made to C. S. Corl, assistant chemist, McLaughlin Gormley King Company for assistance in preparing the various compounds used, and to R. W. Coulter and C. F. Ladeburg, of the same firm, for help in making the tests and counts on citrus. LITERATURE CITED (1) Czapek, F., and Weil, J., Arch. Exptl. Path. Pharmakol., 32, 438 (1893).
(2) Lamiman, J . F., Pacific Rural Press, 125, No. 6 , 94 (1933). (3) MeGregor, E. A . , U. S. Dept. Agr., Farm. Bull. 831 (1931). (4) Morris, H . E . , and Swingle, D . B., J. Agr. Research, 34, No. 1, 59-78 (1927). (5) Nelson, E . M., Hurd-Karrer, A. M . , and Robinson, W. O., Science, in press (1933). (6) Newcomer, E. J., and Yothers, M. A.. U. S . Dept. Agr., Tech. Bull. 89 (1929). (7) Richardson, H. H . , J. Econ. Entomol., 25, 592 (1932). (8) Smith, R. H . , Calif. Agric. Expt. Sta., Bull. 527 (1932). (9) Solis-Cohen, S., and Githens, T., “Pharmaco-therapeutics, Materia Medica and Drug Action,” Appleton, 1928. (10) Wilcomb, H. H., Calif. Cultivator, 78, 387, 403 (1932). (11) Woglum, R. S.,La Follette, J. R . , Landon, W. E., and Lewis, H. C., Handbook of Citrus Insect Control, Calif. Fruit Growers Exchange, 1932. (12) Woodruff, I. O., and Gies, W. J., Am. J. Physiol., 6 , xxix (1902). RECEIVED March 29, 1933.
