i\ I STATE PLANT BOARD March 1947 S-716 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine THE EFFECTIVENESS AND DURATION OF TREATMENTS WITH TECHNICAL DDT IN DIFFERENT SOILS AGAINST LARVAE OF THE JAPANESE BEETLE By Walter E. Fleming and Warren W. Maines, Division of Fruit Insect Investigations When the study of DDT for control of the larvae of the Japanese beetle (Popillia japonica Newm.) was begun in 1943, one problem was to determine whether the nature of the soil was an important factor in the initial effectiveness and the duration of the insecticidal treatment. This phase of the investigation is still in progress, but a report covering the results obtained by the fall of 1946 seems desirable at this time. THE DDT The technical grade of DDT was used in this study. The setting points of the various batches ranged from 91. 2° to 93.9° C. It was prepared for use by micronizing 1/ with an equal weight of pyrophyl- lite. For application as a spray this 50-percent material was sus- pended in water. For application as a dust it was diluted further with pyrophyllite to contain 10 percent of DDT, and 3 percent of tricalcium phosphate was added. LABORATORY STUDIES A study of DDT in 28 soils was undertaken under controlled con- ditions in the laboratory. The soils were obtained from the various soil provinces of New Jersey — the Glacial, the Glacial Lake and River Terrace, the Appalachian Mountain, the Piedmont Plateau, the Limestone Valley, and the Coastal Plain — in order to have soils from the dif- ferent physiographic divisions. Most of these soils also occur in l/This material was micronized through the courtesy of the Micro- nizer Processing Co., Inc., Moorestown, N. J. - 2 - other sections of the country. Each soil was obtained from a sec- tion where, according to the Soil Survey maps issued by the Bureau of plant Industry, Soils, and Agricultural Engineering, it covered a relatively large area. Each soil was identified definitely from the characteristics of its profile and its texture* The soil was* taken largely from the A horizon, the one in which larvae normally occur during the active season. For each sample about 1 cubic yard of the surface layer was removed to a depth of 3 to 6 inches, and passed through a 1/4-inch mesh sieve to remove stones, roots, and other debris. Experimental Procedure The 10-percent DDT dust was thoroughly mixed with 1 cubic foot of each soil at rates equivalent to 25 and 50 pounds of DDT per acre. The volume of soil in an acre to a depth of 3 inches, 10,890 cubic feet, was used as a basis for these treatments. The soil and the DDT ;re mixed by passing the materials through a gyratory riddle several times. Each cubic-foot unit was divided equally among three testing trays, each 18 inches square and 4 inches deep. Groups of 150 field-collected third instars were introduced into each treated sample, and into an untreated sample, of each soil im- mediately after the application of the DDT and at various intervals thereafter. All tests were conducted at a temperature of 80° F« The testing with the batches of larvae introduced 14.6, 74.6, and 127.6 weeks after treatment was discontinued temporarily because they began to pupate during the experimental period, a condition which tends to produce erratic results. During periods when suitable larvae were not available, the soil samples were removed from the testing trays and transferred to earthen pots. These pots were plunged in a bed in an open field, where they remained undisturbed and exposed to the rain, sun, and wind for 35 weeks during the spring, summer, and fall of 1944, for 31 weeks during these seasons in 1945, and for 30 weeks in 1946. Thus, since this investigation has been in progress, the treated soils have been exposed to weathering in the field for more than half of each year. Results were checked at weekly intervals after the introduction of each group of larvae. The soil from each tray was passed through an 8-mesh sieve, which allowed the passage of the soil but not of the larvae. All living larvae, including both the normal and the moribund, were counted and returned with the soil to the testing tray; the dead larvae were discarded. The soil was then watered and reseeded with grass. - 3 - The death rate of the larvae in the untreated soils, due to bacterial disease, nematodes, injury, and other causes, was very low, rarely exceeding 20 percent in tests extending over several weeks. To compensate for these losses the percentage of the larvae killed by each treatment in the different soils was determined by Abbott's formula. Upon completion of observations on a group of larvae, the per- centages of the larvae killed were plotted against the periods of time that the insects had been in the soil. When the mortalities were converted to probits and the intervals of time to logarithms, a linear relationship existed between these factors which could be expressed adequately by a straight line. Time-mortality curves were drawn for each group of 150 larvae introduced into soil treated with DDT. From these curves the time required for the 25- and 50-pound treatments to kill 98 percent of the larvae was determined. 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The tests were conducted under carefully controlled conditions. The temperature was maintained at 80° F« with a variation of * 2°. The soils were kept at their optimum moisture content, and after each examination grass seed was sown to assure an abundant supply of food. As no practical method of rearing a sufficient number of larvae under controlled conditions for tests of this nature has been developed, it was necessary to work with field-collected third-instar larvae. The larvae were col- lected from different localities, were of unknown age, end were stored at a temperature between 45° and 50° F. for different periods before being used in the tests. With stock of this nature greater variability would be expected than with insects reared under controlled conditions. Table 1 shows considerable variation in the time required to kill 98 percent of the different batches of larvae. The average time for the 28 soils ranged from 2.82 to 5.63 weeks with the 25-pound treat- ment and from 2.18 to 3.43 weeks with the 50-pound treatment. The variations were of a rhythmic nature and, it is believed, can be at- tributed largely to the differences in the susceptibility of the batches of larvae. These variations are highly significant and tend to confound the data, making it difficult for one to discern changes in the ipsecticidal value of the DDT treatments. Effect of Soil Type As the surface of soil particles determines to some extent the degree of absorption, a fine-grained soil may be expected to absorb more than a coarse-grained soil. Since absorption in soils is largely a function of the silt, clay, and humus, the type of soil might have an important effect on the insecticidal action of DDT. Sands contain less than 20 percent of clay and silt, gravelly and sandy loams 20 to 50 percent, the loams 50 to 70 percent, and the silt loams more than 70 percent. The average time required to kill 98 percent of the larvae in all soil types was 4 weeks with the 25-pound treatment and 2.7 weeks with the 50-pound treatment. The average periods required in the gravelly and shale loams, sandy loams, loams, and silt loams were not much dif- ferent from" these general averages. It appears that there is little difference in the rates of insecticidal action in these types of soil. In the sands, however, the DDT killed the larvae faster. This would - 9 - suggest that in soil containing 20 -percent or more of clay and silt a certain portion of the DDT may be absorbed and made insectici dally inactive. Effect of the origin of Soil To determine whether the source of the soil might have some ef- fect on the speed of the insecticidal action of DDT, the soils were grouped according to their physiographic provinces, and the average time required to obtain 98 percent mortality of the third-instar lar- vae was calculated for each treatment • These data are summarized in table 2. The glacial soils have been derived from unstratified drift or till; the Glacial Lake and River Terrace soils from stratified glacial deposits; the unglaciated soils of the Appalachian Mountains by weathering of gneiss rock. The Limestone Valley soils have been de- rived by the weathering of limestone. During this process most of the original rock has been carried away in solution, and only the impuri- ties of the original rock are left to make up the main part of the soil. The soils of the Piedmont Plateau have been derived from under- lying crystalline and sedimentary rocks, and the soils of the coastal Plain from unconsolidated sand, clay, gravel, and greensand marl which have been transported from the older land areas and deposited in part under marine conditions. Although there was considerable variation in the speed of in- secticidal action within the different physiographic provinces, tljere was nothing to indicate that the origin of the soil was an important factor. Equally good results were obtained in soils from the Glacial drift areas, the Appalachian L'ountains, the Piedmont plateau, the Limestone Valley, and the Coastal Plain. Effect of Natural Drainage Some of the soils have been developed under conditions of good drainage. In these well-aerated soils there is no interruption in the oxidation processes, and leaching and alluviation are important factors. The minerals are in various stages of oxidation, denitrifi- cation is inhibited, and there is a tendency for nitrates to accumulate, Usually these soils contain little organic matter. Other soils have been developed under conditions of inadequate or poor drainage, so that they are water-lodged for varying periods. In these soils the oxidation processes are depressed, leaching and alluviation are not important factors, and the restricted supply of air favors the accumu- lation of organic matter and the loss of nitrogen. - 10 - Table 2. — Effect of the origin of the soil on the Insecticidal action of DDT against third-instar larvae of the Japanese beetle Average tij ".e required for 98 percent physiographic mortality at in- province Soil series Soil type dicated iosage 25 pounds 50 pounds per acre per acre Weeks weeks Glacial Gloucester Loam 4.07 2.80 Washington Loam 3. OS 2.53 Ttethersfield Gravelly loam 4.52 3.09 Average 3.88 2.81 Glacial Late and Dun ell en Sandy loam 3.56 2.78 River Terrace Merrimac Sandy loam 4.49 2.84 Average 4.03 2.81 Appalachian Berks Shale loam 3.54 2.37 Mountain Chester Loam 3.98 2.65- Average 3.76 2.51 Limestone Valley Hagerstown Silt loam 3.57 2.72 Piedmont Plateau Croton Silt loam 4.99 3.41 Lansdale Gravelly loam 3.25 2.44 Silt loam 3.19 2.52 Penn Shale loam 4.07 2.75 Silt loam 3.53 2.43 Average 3.81 2.71 Coastal Plain Collington Sandy loam 3.62 2.38 Loam 4.92 2.78 Colts Neck Sandy loam 2.75 2.18 Loam 3.98 2.63 Elkton Silt loam 4.43 3.13 Keyport Sandy loam 5.85 3.23 1X3 am 4.52 2 . 86 Lakewood Sand 2.55 2.18 - 11 - Table 2. — (Continued) Physiographic province Soil series Soil type Average time required for 98 percent mortality at in- dicated dosage 25 pounds per acre 50 pounds per acre Weeks Weeks Coastal Plain Portsmouth Sandy loam 4.99 3.07 (Continued) Sassafras Sandy loam 2.61 2.12 Shrewsbury Sandy loam 6.44 3.32 Loam 2.76 2.15 St. Johns Sand 2.95 2.33 Woodstown Sandy loam 5.10 3.12 Loam 5.18 3.10 Average 4.18 2.71 General average 4.02 2.71 Differences required for significance At Vfo level At 5$ level 0.66 .50 0.37 • 28 - 12 - To determine whether the conditions under which a soil had been developed affected the insecticidal action of DDT, the soils were grouped according to their natural drainage and the mortality results averaged for these groups, as shown in table 3. The results indicate that the speed of insecticidal action with ■DDT may be Inhibited in the poorly drained, inadequately aerated soils, both agricultural and nonagricultural. This retardation is probably associated with the higher content of organic matter in these soils, and under natural conditions the high content of water would be a fur- ther inhibiting factor. Some of the DDT may be absorbed by the organic matter and made insecticidally inactive; additions of organic matter to soil tend to retard the mortality of the larvae. The larvae also tend to move less extensively in a medium rich in organic matter than in one made up largely of mineral aggregates, and a longer period is required to kill them. Effect of Mineral Constituents of the Soil Although no complete chemical analysis was made of the soils used in this study, it is known that the different series of soils vary considerably in their composition. Some soils, such as the Lake- wood and Sassafras series, are thoroughly leached and alluviated and tend to be deficient in the fertilizing constituents and other ele- ments, other soils are relatively rich in one or more constituents. Soils of the Colts Neck, Collington, Washington, Penn, and Chester series are rich in iron; soils of the Chester, Penn, and Washington series are rich in aluminum; the Chester, Croton, Berks, Gloucester, and Washington soils are rich in potassium; the Gloucester and Merrimac soils tend to be high in sodium; the Berks, Chester, Gloucester, Lansdale, Merrimac, and Washington soils tend to be high in calcium; and the Berks and the Lansdale soils high in magnesium. In a complex mix- ture such as soil, it is difficult to discern the effect of a single constituent. The speed of insecticidal action with DDT was the most rapid in the thoroughly leached and alluviated soils. It was somewhat retarded in soils rich in iron, aluminum, potassium, sodium, calcium, and magnesium, but the role of each of these minerals in inhibiting the insecticidal action is not known. Duration of Insecticidal Action of DDT No correlation was found between the time required to kill the larvae and the period the DDT was in the soil. So far as could be determined from a statistical analysis of the detailed data in table 1, the effectiveness of DDT did not change significantly during a period of 128 weeks in the soils used in this study. - 13 - Table 3. — "Sffect of natural drainage of soil on the insecticidal action of DDT against third-instar larvae of the Japanese beetle Average time required for 98 percent mortality at in- dicated dosage Soil drainage Soil series Soil type 25 pounds per acre 50 pounds per acre Nonagricultural soils: Weeks Weeks Well drained Lakewood Sand 2.55 2.18 Poorly drained St. Johns Sand 2.95 2.33 .Agricultural soils: • "'ell drained Berks Shale loam 3.54 2.37 "'ell drained Berks Shale loam 3.54 2.37 Chester Loam 3.98 2.65 Collington Sandy loam 3.62 2.38 Loam 4.92 2.78 Colts Neck Sandy loam 2.75 2.18 Loam 3.98 2.63 Dune lien Sandy loam 3.56 2.78 Gloucester Loam 4.07 2.80 Hagerstown Silt loam 3.57 2.72 Lansdale Cra veil y loam 3.25 2.44 Silt loam 3.19 2.52 Merrimac Sandy loam 4.49 2.84 Penn Shale loam 4.07 2.75 , Silt loam 3.53 2.43 Sassafras Sandy loam 2.61 2.12 Washington Loam 3.05 2.53 Wet her sfi eld Gravelly loam 4.52 3.09 Average 3.69 2.59 Imperfectly or Croton Silt loam 4.99 3.41 poorly drained Elk ton Silt loam 4-43 3.13 Keyport Sandy loam 5.35 3.23 Loam 4.52 2.86 Portsmouth Sandy loam 4.99 3.07 Shrewsbury Sandy loam 6.44 3.32 Loam 2.76 2.15 Woods town Sandy loam 5.10 3-12 Loam ^. 18 3-10 Average 4.92 3-04 General average 4-02 2.71 Differences required for signifi cance At 1% level 0.27 0.15 At 5% level .21 .11 - u - FIELD STUDIES In the spring of 1944 field studies were begun to determine the possible value of DDT for controlling the larvae in established turf and for eradicating than in the soil about the roots of nursery plants. Turf Treatment Early in May 1944, four plots totaling 3.1 acres were laid out on the turf of the Passaic County Golf Club. This turf contained on an average 22 Japanese beetle larvae per square foot and ib was rela- tively free of bacterial diseases. The soil was of the Merrimac series and varied in type from a sandy loam to a loam. DDT was applied to the turf as a dust at rates ranging from 24.5 to 36.5 pounds per acre. !*hen the application was completed there was some residue visible en the blades of grass, giving the plots a grayish-white appearance until after the first rain. After the treatment nothing was done to the plots except to mow the grass. These treatments were applied to control the brood which would hatch during the summer and were not expected to have much effect on the population then in the soil. However, when the plots were examined 2 weeks later, .many dead and dying larvae were found. These dying lar- vae showed the characteristic symptoms of DDT poisoning. A survey a month later indicated that two- thirds of the larvae in the plots re- ceiving about 36 pounds of DDT per acre and about one- third of those in the plots receiving 25 pounds per acre were dead. Additional surveys were made of these plots in the fall of 1944, in the spring and fall of 1945, and in the fall of 1946. Fifty dig- gings were made at random over each plot. For each digging a square foot of sod was cut and laid back, the soil was examined to a depth of 4 inches, and all the soil was shaken from the roots of the ^rass and examined. The number of larvae found in each digging in the treated plots and in an adjacent untreated plot are given in table 4. The results obtained were very encouraging. An application of DDT to the surface of the turf at the rate of approximately 25 pounds per acre reduced the population of larvae to negligible proportions. The treatment has been effective for three seasons and from the present indications it might remain effective for several more seasons. - 15 - Table 4. — Effectiveness against third-instar larvae of the Japanese beetle of DDT applied to the surface of soil of the Merrlmac series Date of Dosage Area of treatment Date of Larvae Apparent of DDT plot (1944) survey- found reduction Pounds Square per acre feet Number Percent Check (no treatment) 40,000 Sept. 26, 1944 May 2,1945 583 543 Sept , 13, 1945 681 —- . Sept. 19, 1946 528 25.4 40,000 May 9 Sept. 25, 1944 9 98.5 May 2,1945 4 99.3 Sept. 14, 1945 2 99.7 Sept. 19, 1946 1 99.8 24.5 36,000 10 Sept. 26, 1944 115 80.3 May 2,1945 44 91.9 Sept. 17, 1945 14 97.9 Sept. 20, 1946 1 99.8 35.6 30,000 9 Sept. 26, 1944 49 91.6 May 2,1945 39 92.8 Sept. 17, 1945 12 97.7 Sept. 20, 1946 6 98.9 36.5 30,000 10 Sept. 25, 1944 21 96.4 May 2,1945 15 97.2 Sept. 14, 1945 11 98.4 Sept. 19, 1946 0 100.0 - 16 - Nursery Treatment Studies were begun in 1944 to determine the possibilities of DDT for eradicating larvae in the soil about the roots of nursery plants in beds, frames, and blocks in the field, in order to satisfy the requirements of the quarantine. All the treatments were applied late in the spring or early in the summer to control the summer brood. The treatments were applied at six commercial nurseries that were growing azaleas, blueberries, and various narrow-leaved evergreens in localities scattered over New Jersey. The DDT was applied at rates ranging from 10 to 55 pounds per acre. For the treatment of beds and plots before planting, the DDT was applied as a 10-percent dust to the surface and mixed into the upper 3 to 4 inches by cultivation. For the treatment of established nursery stock the DDT was applied to the surface as a spray. The 50- percent dust was suspended in water and used at the rate of 1,000 gallons per acre. This volume of water was sufficient to moisten the surface of the ground with no hazard of a runoff. In some cases, as with beds of azaleas and blueberries, it was not practical to attempt to mix the material into the soil by cultivation, but wherever possible the plots were cultivated. In September of 1944 and 1945 surveys were made to determine the effectiveness of the various treatments in the nurseries, in making a survey 250 plants per acre were examined in the large plots and a minimum of 50 plants in the small plots (1/5 acre or less). For each examination the plant was removed and sufficient soil shaken from the roots to determine whether larvae were present. Then the hole from which the plant was taken was enlarged to a square foot and examined to a depth of 3 to 4 inches. The results of these surveys are given in table 5. When DDT was applied as a dust or as a spray to the surface of nursery beds and plots at the rate of approximately 25 pounds oer acre and mixed by cultivation with the upper 3 to 4 inches of soil, com- plete elimination of the new brood of larvae was obtained by mid- September. When the material was applied as a spray to the surface and not mixed into the soil, the reduction in the density of the popu- lation was pronounced but complete elimination was not always obtained. - 17 - Table 5. — Effectiveness of DDT applied to soil about the roots of plants in commercial nurseries in New Jersey against third-instar larvae of the Japanese beetle Larvae found in — Check Test plot plot Dosage of DDT Soil series Area of plot Date of treatment Date of survey Plants examined Pounds per acre 10.7 Sassafras 21.0 do. 24.0 Sassafras * peat 25.0 Sassafras 27.0 IVethersfield * peat 30 .0 Sassafras 50.0 do* 55.0 77ethersfield t peat DDT APPLIED AS A 24.0 Sassafras Acres Number Number Number DDT APPLIED AS A DUST 0.25 April 9,1945 Sept. 10, 1945 70 30 4 .25 May- 17,1944 Sept. 27, 1944 70 257 2 Sept.10,1945 70 30 0 .06 May 18,1945 Sept. 10, 1945 100 40 1 1.00 April 9,1945 Sept.10,1945 250 101 0 .27 May 14,1945 Sept. 13, 1945 50 13 0 .25 May 17,1944 Sept. 27, 1944 70 257 0 Sept.10,1945 70 30 0 .25 May 17,1944 Sept. 27, 1944 70 257 0 Sept.10,1945 70 30 0 .21 May 14,1945 Sept. 13, 1945 50 13 0 SPRAY AND MIXED INTO SOIL ABOUT ESTiiBLISHED PLANTS 1.50 June 11,1945 Sept. 12, 1945 380 1,306 - 18 - Table 5. — (Continued) Soil series Area of plot Date of treatment Date of Survey Plants examined Larvae found in — Dosage of DDT Check plot Test plot Pounds per acre Acres Number J timber !Tumber DDT APPLIED AS k SPRAY TO ESTABLISHED BEDS AND NOT MIXED INTO SOIL 10.0 Sassafras 0.01 July 10,1944 Sept. 27,1944 70 257 12 24.6 do. .10 June 13,1945 Sept. 12,1945 50 45 14 E5.0 do. .01 July 10,1944 Sept. 27,1944 70 257 1 25.0 Lakewood ♦ peat .002 June 6,1945 Sept. 21,1945 528 0 25.0 Lakewood ♦ peat .002 June 6,1945 Sept. 21,1945 238 0 25.0 Lakewood * peat .002 June 6,1945 Sept. 21,1945 267 0 28.4 Sassafras .15 June 13,1945 Sept. 12,1945 60 54 11 29.8 do. .44 June 13,1945 Sept. 12,1945 150 135 12 50.0 do. .01 July 10,1944 Sept. 27,1944 70 257 1 19 - The soils treated in the commercial nurseries were of the Sassafras, Talt<"iwood , and 'Vethersfield se3*ies, and in some cases were modified by the addition of peat and roanureo There was some indica- tion tha^whan applied to the surface of a plot and not cultivated into the soil, the DDT was more effective in the Lakewocd than in tho .Sassafras series, but another factor, namely, the type of plant in the plot, might have influenced the results. ',rhen the DDT was mixed with the upper 3 to 4 inches of soil? there was no difference in its action in the 3aasafras and in the './ethersfield series. In the; plots left intact in commercial nurseries for tjwo seasons* a treatment applied at the rate of approximately 25 pounds per acre eliminated two subsequent annual broods of larvae and, from present indications, it may eliminate one or more additional broods. There was nothing to suggest that the insecticidal value of the treatments had deteriorated under conditions in the commercial nurseries. SUMMARY A study of the influence of different soils on the insecticidal action of technical DDT against the larvae of the Japanese beetle was begun in 1943. This investigation is still in progress, but the results obtained by the fall of 1946 are reported. In preliminary laboratory studies the DDT was applied as a 10- percent dust at rates equivalent to 25 and 50 pounds per acre to 28 soils, including 21 series and 6 types, from 6 physiographic soil divisions.. The results may be summarized briefly as follows; 1. The speed of insecticidal action was faster in the sands than in the other types of soil, but there was no significant difference in the rates in the gravelly loams, shale loams, sandy loams, silt loams, and loams. ° The origin of the soil did not seem to be an important factor. Equally as good results were obtained in soils from the Glacial drift areas, the Appalachian Mountains, the Piedmont Plateau, the Limestone Valley, and the Coastal Plain. 3. The speed of insecticidal action may be inhibited in poorly drained, inadequately aerated soils. This re- tardation is probably associated with the higher content of organic matter in these soils. UNIVERSITY OF FLORIDA ran nun 3 1262 09239 1456 4. The insecticidal action was the most rapid in the thoroughly leached and alluviated soils. It was somewhat retarded in soils rich in iron, aluminum, potassium, sodium, calcium, and magnesium, but the role each of these minerals has in inhibiting the action is -not known. 5* No correlation was found between the effectiveness of DDT and the period the material had been in the soil. So far as could be determined, the effectiveness of DDT against the third-instar larvae did not change significantly during 128 weeks in the 28 soils used in this study. In the field studies DDT was applied at rates ranging from 10 to 55 pounds per acre to soils of the Sassafras, L!errimac, Lakewood and Wether sfield series. All the treatments were applied in the spring with the object of poisoning the brood which would hatch during the summer. The DDT was applied to established turf and in commercial nurseries to eradicate the larvae in the soil about the roots of nur- sery stock. The results may be summarized as follows: 1* A 10-percent DDT dust applied to the surface of established turf at the rate of 25 pounds of DDT per acre caused a significant reduction in the larval population then in the soil and reduced the density of three sub- sequent annual broods to negligible proportions. 2# When DDT was applied as a 10-percent dust or as a spray to nursery beds and plots at the rate of 25 pounds of DDT per acre and mixed by cultivation with the upper 3 to 4 inches of soil, two subsequent 8nn>ir,"> broods were completely eliminated by mid-Septem