UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA NEW MATERIALS FOR CONTROL OF THE MEALY PLUM APHID LESLIE M. SMITH and CURTIS A. FERRIS BULLETIN 671 October, 1942 UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE Annual cycle 3 Materials and methods used 5 Control studies, 1937-38 7 Control studies, 1938-39 9 Concentration and field efficiency of material no. 9 10 Use of dinitro-o-cyclohexylphenol without petroleum oil 11 Dinitro-o-cyclohexylphenol used with asphalt vs. paraffin oils 12 Use.of acid or base with dinitro-o-cyclohexylphenol 12 Mixtures prepared in the spray tank 13 Other materials tested in 1938-39 14 Control studies, 1939-40 15 Concentration and field efficiency of material no. 13A 15 Effect of wetting agent in no. 13A 15 Use of oil with material no. 13A 17 Comparison of materials no. 11 and no. 13A 17 Effect of rain on materials no. 13A and no. 13C 17 Other dinitro phenols tested in 1939-40 19 Control of two scale insects on plum trees 21 Control of brown apricot scale 21 Control of Italian pear scale 23 Effect of dinitro compounds on covercrops and trees 25 Care in handling dinitro cresols and phenols 28 Summary 28 Acknowledgments 30 NEW MATERIALS FOR CONTROL OF THE MEALY PLUM APHID 1 LESLIE M. SMITH 2 and CURTIS A. FERRIS 3 The mealy plum aphid, Hyalopterus pruni (Geoff.), may injure plum and prune orchards in three ways as discussed in Bulletin 606 4 : (1) curling and stunting of the foliage, together with a reduced growth in length of new wood and a general stunting of the trees; (2) soiling of the surface and bloom of table fruits by aphid excrement and the fre- quently associated black sooty molds ; (3) splitting of the fruit. Control of the mealy plum aphid has been studied at the California Agricultural Experiment Station since 1928. In Bulletin 606, spraying with coal-tar distillates was presented to the growers as a cheap and effective method of control on the basis of experiments conducted by the senior author prior to 1936. The chief disadvantage is that tar sprays are caustic to men. Since this report was made, other materials have become commer- cially available, some of which are allegedly aphid ovicides, while others are not so described by the manufacturers. Among these are a number of nitrated phenolic derivatives. One such material, 3, 5-dinitro-o-cresol (reported by Tattersfield, Gimingham, and Morris 5 ), was tested at this station as early as 1930-31 and found to be highly toxic to aphid eggs. But at that time the only source for this compound was quoted at a price of $10 a pound, so that the experiments were not continued. Present prices of similar compounds, however, are not preclusive to their use. During the winters of 1937-38, 1938-39, and 1939-40, a number of new spray materials were tested. Some of these proved superior to coal- tar-distillate sprays. This bulletin presents the results of that research. ANNUAL CYCLE Before control studies can be properly presented, however, the com- plicated annual cycle of this aphid must be reviewed. This has been done rather completely in previous papers 6 ; the following brief summary is taken from Bulletin 606. 1 Received for publication August 7, 1941. 2 Assistant Entomologist in the Experiment Station. 3 Technical Assistant in Entomology; resigned June 30, 1940. 4 Smith, Leslie M. Control of the mealy plum aphid. California Agr. Exp. Sta. Bui. 606:1-34.1937. 5 Tattersfield, F., C. T. Gimingham, and H. M. Morris. Studies on contact insecti- cides. Part III. Ann. Appl. Biol. 12:218. 1925. 6 For a more complete discussion of the life history of this pest see : Smith, Leslie M. Biology of the mealy plum aphid, Hyalopterus pruni (Geoff roy). Hilgardia 10(7) H67-211. 1936. Smith, Leslie M. Growth, reproduction, feeding, and wing development of the mealy plum aphid in relation to climatic factors. Jour. Agr. Res. 54(5) :345-64. 1937. [3] 4 University of California — Experiment Station The mealy plum aphids pass the winter in the egg stage on the plum trees. The eggs (fig. 1) are found near the bases of the buds, and most commonly between the bud and the twig. They hatch in the spring shortly after the buds start to swell, and are practically all hatched by the time 5 per cent of the flowers are in bloom. The aphids which emerge from the overwintered eggs are known as the stem mothers. They are wingless, green in color, and match the color of the young leaves. Unlike the genera- Fig. 1. — Egg of the mealy plum aphid, Hyalopterus pruni (Geoff.), at the base of a bud. (From Hilgardia vol. 10, no. 7.) tions that follow, they are devoid of the white waxy powder which is characteristic of this species and which has given rise to its common name. All of the aphids from the overwintered eggs are females and give birth parthenogenetically (that is, with- out fertilization) to other wingless, parthenogenetic females. Several similar generations (3 to 7) occur on the plum trees, but with the advent of warm summer weather in June and July, the young, when matured, have wings and can no longer feed on the plum tree. These winged females fly to reed grass or cattails, where they give birth parthenogenetically to wingless aphids, identical in appearance to those of the spring generations on the plum. Here several generations of wingless females mature during the late summer and fall. In the latter part of October and throughout November, winged aphids are pro- Bul. 671] New Materials for Control of the Mealy Plum Aphid 5 duced on the secondary hosts. They are unable to feed on the secondary hosts, after reaching maturity, and must fly back to the plum trees. The first winged aphids that are produced are all parthenogenetic females, which after arriving on the plum give birth to young that mature to small, wingless, sexual females. The winged aphids produced somewhat later on the secondary hosts are males, which fly to the plums and mate with the wingless sexual females. After mating, these females lay the overwintering eggs. The movement of aphids from tree to tree and from orchard to orchard is of pri- mary importance in any consideration of control. Contrary to the popular belief, the winged aphids developed on the plum are incapable of feeding on or producing young on the plum and must migrate to the secondary hosts. This has been demonstrated by repeated cage tests and by field evidence. In certain orchards the aphids are found year after year on certain trees while other trees are always free from aphids. This fact has given rise to the popular mis- conception that the aphids complete their annual cycle on the plum, and doubt is thereby thrown on the necessity for secondary hosts. In cases of this kind, it can generally be shown that the infested trees are near a windbreak, such as a barn or row of tall trees. The aphids, returning from the secondary hosts in the fall, settle on trees in such sheltered situations. Conclusive proof has been obtained that the aphids cannot complete their annual cycle without passing a part of the year on a secondary host. 7 MATERIALS AND METHODS USED All of the control measures studied and reported in this bulletin con- sist of ovicidal sprays applied in the winter, or when the trees are fully dormant. The materials tested are as follows : 1. A proprietary petroleum-oil emulsion, said to contain secret toxic materials which might act as an aphid ovicide. 2. Phenothiazine (or thiodiphenylamine). 3. Dinitro-o-cyclohexylphenol. 4. Sodium salt of dinitro-o-cyclohexylphenol. 5. A solution of 2.5 per cent o-nitrophenol in an emulsive dormant oil. 6. Tar-oil vapor spray applied as an inverted emulsion. 7. A proprietary coal-tar-distillate emulsion. 8. Another proprietary coal-tar-distillate emulsion. 9. A proprietary solution of 4 per cent dinitro-o-cyclohexylphenol in dormant-grade, eastern, petroleum oil. 10. o-Nitrophenol. 11. Sodium dinitrophenolate, as a solution and suspension in water, containing 20 per cent by weight of sodium dinitrophenolate, and 10 per cent by weight of a secret "penetrant," hereinafter called a wetting agent. 12. A proprietary oil emulsion containing certain nitro compounds and said to contain 75 per cent petroleum oil. 13. A solution and suspension in water of sodium dinitro-o-cresolate, 7 Smith, Leslie M. Control of the mealy plum aphid. California Agr. Exp. Sta. Bul. 606:3-5. 1937. 6 University of California — Experiment Station 20 per cent by weight, with the remainder being water and wetting agent. The manufacturers furnished three types of sodium dinitro-o- cresolate mixtures : no. 13C, containing no wetting agent; no. 13H, con- taining 5 per cent wetting agent ; and no. 13A, containing 10 per cent wetting agent. (Nos. 13C and 13H were experimental mixtures and no.'13A was the proprietary mixture as marketed.) 14. Similar to no. 13A, except that the concentration of sodium dinitro- o-cresolate was 30 per cent and no wetting agent was added. 15. A triethanolamine salt of dinitro-o-cyclohexylphenol. 16. A proprietary mixture of 2,4-dinitrophenol (2,6 isomer less than 3 per cent) dissolved at the rate of 1.86 ounces of dinitrophenol per gallon of oil and emulsified. 17. Similar to no. 16, but with twice the concentration (3.72 ounces per gallon) of dinitrophenol. 18. A proprietary mixture of 2,4-dinitrophenol dissolved in oil at the rate of 3.0 ounces per gallon and emulsified. These materials are referred to elsewhere in the text by number. Materials 1 to 9 were tested during the winter of 1937-38 ; materials 10 to 14 during the winter of 1938-39; and materials 15 to 18 during 1939-40. The stock mixtures were prepared in the following manner : 300 grams of phenothiazine (material no. 2) was mixed with 8 liters of tank-mix oil with a specific gravity of 0.9. The phenothiazine was worked in 200 cc of oil to a thick paste with an electric mixer. The paste was worked through a % 4 -inch-mesh screen into the bulk of the oil. How much of the phenothiazine went into solution in the oil is not known, but prob- ably not more than 10 per cent by weight. The remainder was sus- pended in the oil by stirring, then poured into the spray tank with the agitator running. Dinitro-o-cyclohexylphenol crystals were added to cold tank-mix oil until a concentration of 3 per cent was reached. No more powder would dissolve in the oil. The sodium salt of dinitro-o-cyclohexylphenol (1,296 grams) was dis- solved in 9 quarts of acetone to which 163 grams of a wetting agent was added. When 2 quarts of this mixture was used per 100 gallons of- water, the molal concentration of the sodium salt was the same as when 2% gallons of 3 per cent dinitro-o-cyclohexylphenol was used per 100 gallons. In the field, dinitro-o-cyclohexylphenol crystals were added to the spray tank with the agitator running. Little, if any, of the crystals dissolved. Caustic soda was added slowly until all of the crystals dis- solved. When this was accomplished, 6 ounces of caustic soda per 100 gallons had been added. The dinitro-o-cyclohexylphenol reacts chemi- Bul. 671] New Materials for Control of the Mealy Plum Aphid 7 cally with the caustic soda to form the sodium salt. This salt is reddish orange, and when dry it is very irritating to the nose and throat. The method of preparing the sodium salt of dinitro-o-cyclohexylphenol in the spray tank is preferable to using the dry powder for this reason. In one case of the dinitro-o-cyclohexyphenol tests (plat 6, table 1) wherein the crystals were dissolved in the petroleum oil, oxalic acid was TABLE 1 Angier Orchard, Sprayed February 16 and 24, 1938 Plat Material and amount per 100 gallons of water (except as noted) sprayed Amount of spray per tree Trees Heavily infested Lightly infested Clean None, check No. 5, 2 gals None, check 4 per cent no. 5 in oil, 5 gals.; water, 5 gals, only No. 6, 10 gals.; water, 10 gals, only 3 per cent no. 3 in tank-mix oil, 1Yi gals. ; blood albumin, 6 oz.; oxalic acid, 4 oz.. . No. 4 in acetone plus wetting agent, 2 qts. None, check No. 9, 2 l A gals.; blood albumin, 6 oz.; oxalic acid, 4 oz None, check Tank-mix oil, 2H gals. ; blood albumin, 6 oz No. 1,2^ gals None, check 4 per cent no. 2 in tank-mix oil, 2 l A gals. ; blood albumin, 6 oz No. 3, \i lb.; caustic soda, 6 oz No. 8, 3 gals number 17 33 17 26 34 36 32 18 gallons 5.76 0.23 0.35 5.15 2.34 4.17 4.44 4.72 4.32 per cent 100.0 100 100.0 100.0 3.0 0.0 100.0 0.0 100.0 100.0 94.4 93.9 100.0 0.0 19.0 per cent 0.0 0.0 0.0 0.0 26.6 19.4 3.1 0.0 3.8 0.0 0.0 5.6 6.1 0.0 2.3 23.0 per cent 0.0 0.0 0.0 0.0 70.4 80.6 96.9 0.0 96.2 0.0 0.0 0.0 0.0 0.0 97.7 58.0 * Dashes indicate data not available. added to the water in the spray tank to neutralize any base present and thereby prevent the dinitro-o-cyclohexylphenol from leaving the oil and going into solution in the water. CONTROL STUDIES, 1937-38 The materials tested during the first winter were materials nos. 1 to 9. The sprays were applied to President plums on the Angier orchard at Lodi, San Joaquin County (table 1), and to Grand Duke and Diamond plums on the Lynwood (table 2) and Highland (table 3) orchards at Penryn, Placer County. Counts were made from May 1 to 15. Each tree was carefully inspected, and if no aphids were found, it was counted as "clean" ; if from one to three colonies were found, the tree was counted as "lightly infested" ; and if four or more colonies were found, the tree was counted as "heavily infested." 8 University of California — Experiment Station In considering the data in tables 1 to 3, more dependence can be placed on the Angier tests than those on Lynwood and Highland. The infesta- tion on the Angier orchard at Lodi was heavy and uniform, whereas at TABLE 2 Lynwood Orchard, Sprayed February 24, 1938 Plat no. Material and amount per 100 gallons of water Trees sprayed Amount of spray per tree Trees Heavily infested Lightly infested Clean 1 2 3 None, check None, check number 20 38 34 36 31 34 gallons 2.79 2.22 2.74 2.94 per cent 100.0 86.9 32.4 0.0 77.4 14.7 per cent 0.0 10.5 38.2 19.4 16.1 26.5 per cent 0.0 2.6 29.4 4 5 No. 9, 2y-cresolate (proprietary 20 per cent mixture in water) is marketed in 1-gallon cans, which are about half full of solid material that settles to the bottom. Before a representative sample is poured from the can, the sodium dinitro-o-cresolate must be unif ormily suspended in the solution. If the full cans are placed upside down on the spray rig, vibration and movement of the rig will wash the heavy material from the bottom of the can and deposit it loosely against the lid of the inverted can. When the lid is removed, the solid material is then much more easily mixed with the solution. When it is allowed to dry completely, in thick layers or chunks, it is highly flammable. Care must be taken, therefore, to avoid spilling the concentrate around buildings; and spray rigs should be thoroughly washed at the conclusion of the spray work. It should not be left in open cans and allowed to dry. This material is a dye with a particular affinity for woolen cloth. When strips of cloth were dyed in a saturated solution of this chemical and dried, they burned more slowly than untreated cloth. The dinitro phenols and cresols discussed herein will dye human skin and hair yellow. This can be removed only with difficulty by repeated washings with soap. SUMMARY This study pertains exclusively to winter sprays, applied when the trees are fully dormant, for the control of the mealy plum aphid, Hyalop- terus pruni (Geoff.), which is present on the trees during the winter, in the egg stage. Observations on scale control and effect on covercrop are included. Preliminary studies eliminated several diverse materials, and nar- rowed the possibilities to certain dinitro compounds. Two of these, namely, dinitro-o-cyclohexylphenol, and sodium dinitro-o-cresolate were studied extensively. Four per cent dinitro-o-cyclohexylphenol dissolved in petroleum oil (material no. 9) and emulsified as a tank mix yields satisfactory control when used at 2 gallons of this solution per 100 gallons of water. Twenty per cent sodium dinitro-o-cresolate (material no. 13A), used as a solution in water, yields a satisfactory control when used at 3 pints (12 ounces dry weight) per 100 gallons of water. Dinitro-o-cyclohexylphenol without oil (material no. 3) yielded better control than when oil was used with it. When tested in eastern, paraffin- base vs. western, asphalt-base oils, no difference in efficiency was found. Dinitro-o-cyclohexylphenol (material no. 3) was tested in acidic, in Bul. 671 ] New Materials for Control of the Mealy Plum Aphid 29 basic, and in unmodified water, and the efficiency increased with an increase in pH. Material no. 9 (a proprietary mixture of dinitro-o-cyclohexylphenol in dormant oil) was most efficient in unmodified water, less efficient in basic, and least efficient in acidified water. Sodium dinitro-o-cresolate (20 per cent by weight), as marketed (material no. 13A), contains 10 per cent "penetrant," or wetting agent. Tests of sodium dinitro-o-cresolate containing 0, 5, and 10 per cent by weight of wetting agent indicated that the wetting agent slightly reduces the efficiency of this material. Sodium dinitro-o-cresolate combined with oil was reduced in efficiency — the less oil, the lower the efficiency until an undetermined low was reached. The efficiency of this material with 2 gallons of oil per 100 gallons of water, however, nearly approximates that of the material alone. Sodium dinitrophenolate (material no. 11), was markedly inferior to sodium dinitro-o-cresolate (material no. 13A). The proprietary solution of 4 per cent dinitro-o-cyclohexylphenol in petroleum oil (material no. 9) used at 1 gallon per 100 of water yields a satisfactory control of brown apricot scale. Dinitro-o-cyclohexylphenol at 2 and 4 ounces per 100 gallons of un- modified, of acidic, or of basic water failed to yield a satisfactory control of scale. Dinitro-o-cyclohexylphenol at 4 ounces with 2 gallons of oil per 100 gallons yielded a satisfactory control of brown apricot scale. The addi- tion of acid or base to the above mixture decreased the kill of scale. Sodium dinitro-o-cresolate (20 per cent by weight) used alone at 3 pints per 100 gallons did not satisfactorily control brown apricot scale. When this concentration was used with 2 gallons of oil per 100 gallons of water, the control of scale was satisfactory. Neither of these dinitro compounds was effective against the Italian pear scale. Both of these compounds injure the covercrop, and the extent of the injury is determined by many variable factors. No damage to the trees resulted from any dormant applications. Severe injury occurred when these compounds were applied to trees which were starting to bloom. Early-fall applications of dinitro phenols and cresols, without oil, present interesting possibilities in special cases. 30 University of California — Experiment Station ACKNOWLEDGMENTS The authors wish to express their appreciation to the several growers mentioned in this paper, all of whom contributed valuable aid. The Penryn Fruit Company assisted in tests on their orchards, Franklin, Highland, Bellevue, Palms, and Club. Assistance was rendered through Work Projects Administration Official Project No. 465-03-3-168. 12m-ll, '42(3176)