December 1950 E-811 
 
 United States Department of Agriculture 
 
 Agricultural Research Administration 
 
 Bureau of Entomology and Plant Quarantine 
 
 INSECTICIDE DUSTS TO CONTROL THE CLOVER ROOT BORER 
 AND THE MEADOW SPITTLEBUGI/ 
 
 By B. A. App and Ray T. Everly,-a -' 
 Division of Cereal and Forage Insect Investigations 
 
 The clover root borer (Hylastinus obscurus (Marsh.)) has been 
 recognized as an important pest of red clover for many years. During 
 the last three seasons considerable numbers have been observed in red 
 clover fields in Ohio, and a large percentage of the roots in second-year 
 red clover fields have been infested. The control of this root borer with 
 insecticides has been difficult because of the protected location of the 
 larvae within cavities or tunnels which they gnaw in the roots. During 
 the last few years, however, treatment with the new organic insecticides 
 has given very encouraging results. Experiments conducted by Marshall 
 ej aj. ( 1_) in 1946, 1947, and 1948 showed that technical benzene hexa- 
 chloride at 1.5 pounds of the gamma isomer per acre gave excellent 
 control of the clover root borer. 
 
 1/ This research was conducted at the Legume Seed Research 
 Laboratory maintained by the Bureau of Entomology and Plant Quarantine 
 and the Bureau of Plant Industry, Soils, and Agricultural Engineering, in 
 cooperation with the Ohio State University and the Ohio Agricultural 
 Experiment Station. The studies were made at the Ohio Hybrid Seed Corn 
 Producers' research farm at Croton, Ohio. 
 
 2/ Resigned June 30, 1948. Now associate in entomology, Purdue 
 Agricultural Experiment Station, Lafayette, Ind. 
 
 3j The authors appreciate the cooperation of John G. Dean, Jr., of 
 the Bureau of Plant Industry, Soils, and Agricultural Engineering, A. W. 
 Woodrow, of the Bureau of Entomology and Plant Quarantine, and Ralph H. 
 Davidson, of the Ohio State University. Theodore Davich and Elbert L. 
 Sleeper, of the Bureau of Entomology and Plant Quarantine, and Russell 
 Secrest, of the Bureau of Plant Industry, SoilSi and Agricultural Engin- 
 eering, assisted in the field work. Richard M. Hiatt, of the Ohio State 
 University, assisted in the application of insecticides and calculated the 
 seed yields in 1948. 
 
Since 1947 experiments have been carried on at Croton, Ohio, with 
 dilute dusts of various insecticides applied to the plant crowns and surface 
 of the soil in plots of young clover. Applications in the fall to first-year 
 clover or in the spring to second-year clover have been tried. 
 
 The tests were planned primarily to control the clover root borer, but 
 it was noted in the spring of 1948 that some of the treatments had provided 
 excellent control of the meadow spittlebug ( Philaenus leucopthalmus (L,)). 
 This insect has been very abundant in Ohio legume fields for several years. 
 During the 1948-49 season data were taken to determine the possibility 
 of controlling these two important red clover pests with the same 
 treatment. 
 
 Red clover is usually seeded in the spring as a companion crop of 
 wheat or oats. The clover continues to grow after the grain crop is 
 harvested, but as a rule no clover hay or seed is gathered the first season. 
 In the second year after planting a hay crop is cut in June and either a 
 second hay crop or a seed crop is harvested in August. The clover root 
 borer infests red clover in the spring of the second year. When the in- 
 festation is heavy, many plants are so weakened that they do not recover 
 after the June hay crop is cut. The stand remaining for the seed crop or 
 for second-crop hay is thus much reduced. The meadow spittlebug also 
 attacks second-year clover. Severe infestations stunt plant growth and 
 cause general loss of vigor. 
 
 Tests Conducted During 1947-48 
 
 During 1947-48 DDT, benzene hexachloride, and chlordane dusts were 
 tested in four replications of 9- by 12-foot field plots of red clover 
 arranged in a randomized block. The dusts were applied with a hand 
 fertilizer spreader that treated a strip of clover 36 inches wide. Each 
 insecticide was applied seven times, and one set of plots was left un- 
 treated to serve as a check. DDT and chlordane were applied at the rate 
 of 500 pounds of a 1 -percent dust per acre. In the fall treatments 
 technical benzene hexachloride was used at the rate of 100 pounds of dust 
 containing 1 percent of the gamma isomer and in subsequent treatments 
 at 500 pounds of a dust containing 0.25 percent of the gamma isomer. 
 
 Samples of roots were dug and dissected in the field during the period 
 August 18-24, 1948. On each digging date three roots were dug from 
 each of five points in each plot. If by chance more than three roots were 
 dug, they were also examined and recorded. The results of these 
 treatments are given in table 1. 
 
 An analysis of the data by the variance method showed that, when 
 < ompared with untreated plots, there was significant reduction in the 
 percentage of infested roots from all treatments with technical benzene 
 hexachloride and chlordane. Applications of DDT did not cause any 
 marked reduction in the percentage of roots infested. In this test the 
 
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 differences caused by the time or number of applications were not 
 significant. However, a single application of any of the materials in the 
 spring was slightly more effective than single applications the previous 
 August or September. Furthermore, plots given both a fall and a spring 
 treatment of technical benzene hexachloride or chlordane contained fewer 
 infested roots than those given only one treatment. 
 
 On August 19, 1948, clover on 2 square yards from each plot was cut 
 and threshed to determine the seed yields. An analysis of the data showed 
 that none of the differences were significant, because there was so much 
 variation among the samples from the different plots. The yield of clover 
 seed was slightly higher from most of the treated plots than from the 
 untreated check. 
 
 Tests Conducted During 1948-49 
 
 In the tests conducted during 1948-49 a randomized-block arrange- 
 ment was used, the size of the plots was increased to 9 by 18 feet, and 
 the treatments were replicated five times instead of four. In addition to 
 the materials previously tested, parathion, toxaphene, methoxychlor, and 
 aldrin were used in the spring tests. All the materials were applied as 
 dilute dusts with a fertilizer spreader in the same way as in 1947-48. 
 One set of plots was treated on September 13, 1948, a second set on 
 May 3, 1949, and a third set on both dates. A set of untreated plots was 
 maintained as a check. 
 
 Samples of roots were dug and dissected during the period August 15-17, 
 1949, to determine the effect of the treatments on the clover root borer 
 population. As in the previous experiment, three roots were dug at each 
 of five points in each plot. On each digging date an equal number of roots 
 was dug from each plot. 
 
 Of the materials applied on September 13, 1948 (table 2), by far the 
 largest reductions in number of borers per root were caused by benzene 
 hexachloride and chlordane. Parathion and DDT were much less effective 
 at the dosages used. 
 
 For the different treatments applied May 3, 1949, the descending 
 order of efficiency at the dosages used was chlordane, aldrin, technical 
 benzene hexachloride, parathion, toxaphene, methoxychlor, and DDT 
 (table 2). Parathion averaged 0.87 borer per root when applied as a 
 spring treatment, as compared with 3.39 borers when applied in the fall. 
 
 Two applications, in the fall and in the spring, were not more effective 
 than a single application in either fall or spring. Excellent control was 
 obtained with chlordane, benzene hexachloride, and parathion. Judging 
 from the results, however, it seems probable that the effectiveness of 
 parathion was derived mainly from the spring application. DDT was 
 comparatively ineffective. 
 
5- 
 
 Table 2. --Effect of various insecticides applied to red clover in 
 
 September 1948 and May 1949 on populations of the clover root borer 
 in August 1949 
 
 
 Active 
 
 
 Average 
 
 Total 
 
 Reduction 
 
 Insecticide 
 
 ingredient 
 
 Roots 
 
 borers 
 
 borers 
 
 in total 
 
 
 per acre 
 
 infested 
 
 per root 
 
 in sample 
 
 population 
 
 
 Pounds 
 
 Percent 
 
 Number 
 
 Number 
 
 Percent 
 
 Applications on 
 
 September 13, 1948 
 
 
 None 
 
 
 
 76 
 
 5.88 
 
 441 
 
 
 
 DDT 
 
 5 
 
 83 
 
 5.17 
 
 388 
 
 12.0 
 
 Benzene hexachloride, 
 
 
 
 
 
 
 gamma isomer 
 
 11/4 
 
 1 
 
 .03 
 
 2 
 
 99.5 
 
 Chlordane 
 
 5 
 
 13 
 
 .21 
 
 16 
 
 96.4 
 
 Parathion 
 
 5 
 
 69 
 
 3.39 
 
 254 
 
 42.4 
 
 Applications on May 
 
 3, 1949 
 
 
 
 None 
 
 
 
 76 
 
 5.88 
 
 441 
 
 
 
 DDT 
 
 5 
 
 57 
 
 3.89 
 
 292 
 
 33.8 
 
 Benzene hexachloride, 
 
 
 
 
 
 
 gamma isomer 
 
 1 1/4 
 
 16 
 
 .81 
 
 61 
 
 86.2 
 
 Chlordane 
 
 5 
 
 15 
 
 .33 
 
 25 
 
 94. 3 
 
 Parathion 
 
 5 
 
 24 
 
 .87 
 
 65 
 
 85.3 
 
 Toxaphene 
 
 5 
 
 40 
 
 2.15 
 
 161 
 
 63.5 
 
 Methoxychlor 
 
 10 
 
 61 
 
 2.93 
 
 220 
 
 50. 1 
 
 Aldrin 
 
 2 
 
 16 
 
 .43 
 
 32 
 
 92.7 
 
 
 Applications on both dates 
 
 
 
 None 
 
 
 
 76 
 
 5.88 
 
 441 
 
 
 
 DDT 
 
 10 
 
 64 
 
 4.21 
 
 316 
 
 28.3 
 
 Benzene hexachloride, 
 
 
 
 
 
 
 gamma isomer 
 
 2 1/2 
 
 4 
 
 .04 
 
 3 
 
 99.3 
 
 Chlordane 
 
 10 
 
 
 
 
 
 
 
 100.0 
 
 Parathion 
 
 10 
 
 12 
 
 .43 
 
 32 
 
 92.7 
 
 Difference required 
 
 
 
 
 
 for significance 
 
 19:1 
 
 16 
 
 1.56 
 
 
 
 
 
 
 99:1 
 
 21 
 
 2.07 
 
 
 
 
 
There was only a fair stand of clover in any of the plots. Examination 
 just after the hay was cut showed less than 50 percent of a stand. A good 
 many plants died after the first cutting, and many of the others made very 
 poor recovery. This mortality was believed to be due largely to clover 
 diseases. The field also lacked pollinators, because an adjacent field of 
 white sweetclover attracted the honeybees away from the red clover. There- 
 fore, no seed was harvested from this field by the grower, and it was impos- 
 sible to take samples from which reliable yields of seed per acre could be 
 calculated. 
 
 An attempt to obtain some information on the effect of the clover root 
 borer on seed production was made by harvesting all the heads from a 
 10-stem sample taken at random in each plot and dissecting 10 heads in 
 each sample to determine the average number of florets per head and the 
 percentage of florets producing seed. To determine the average number 
 of seeds per head all the heads in the 10-stem sample were threshed and 
 the seeds counted. None of the differences recorded proved to be signif- 
 icant, but some of the results were interesting. In all the treated plots 
 except those where DDT or methoxychlor was used there was a slight in- 
 crease in the number of florets per head over untreated plots. Regardless 
 of the date of application, the heads taken from the plots treated with benzene 
 hexachloride had more florets than those taken from plots treated with other 
 materials. Heads from some of the treated plots showed a larger percent- 
 age of florets producing seed than heads from untreated plots. The samples 
 of clover from the treated plots showed a higher average number of seeds 
 per head than those from untreated plots (table 3). 
 
 Effect on the Meadow Spittlebug of Insecticide Treatments for 
 Control of the Clover Root Borer 
 
 In the spring of 1948 it was observed that certain of the treatments 
 for the root borer had given good control of meadow spittlebug nymphs. 
 Benzene hexachloride applied in August and September 1947 at the rate 
 of 1 1/4 pounds of the gamma isomer per acre reduced the nymphal pop- 
 ulation of spittlebugs the following May by 97 percent, and DDT at 5 pounds 
 per acre reduced it by 76 percent. Applications in May 1948 of benzene 
 hexachloride and DDT at the same rates and of chlordane at 5 pounds per 
 acre gave practically 100 percent control of spittlebug nymphs. 
 
 During 1949 more detailed data were taken to determine the possibility 
 of controlling both the clover root borer and the meadow spittlebug with 
 the same treatment. On May 12, 25 stems were selected at random in 
 each plot. The stems were examined and the number of spittlebug nymphs 
 was recorded. As a result of the previous fall treatments technical benzene 
 hexachloride, chlordane, and DDT reduced the spring population of spittle- 
 bug nymphs 99.2, 95.5 and 83 percent, respectively. Spring treatments 
 with all these materials were 99 to 100 percent effective,as were the treat- 
 ments in both fall and spring. There is therefore no advantage in treating 
 the same plots in both the fall and spring. Parathion, of no value as a fall 
 
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 treatment proved 87 percent effective as a spring application. Methoxychlor, 
 aldrin, and toxaphene, tested only in the spring, furnished excellent control. 
 
 The results of these tests indicate that the same treatment will control 
 both the clover root borer and the meadow spittlebug. From the standpoint 
 of harmful residues in the June hay crop, fall applications would probably 
 be preferable, but applications late in April or early in May should be 
 made 4 to 6 weeks before the hay is cut, and because the plants are very 
 small at this time it is believed little treated foliage should be included in 
 that cut for hay. Information is needed on the insecticide residue hazard, 
 if any, as well as more data on the most effective and economical dosages 
 and methods of application. The danger of causing off flavor in vegetable 
 root crops subsequently grown in soils that have been treated with benzene 
 hexachloride must also be considered. 
 
 Summary 
 
 Replicated experiments for control of the clover root borer (Hylastinus 
 obscurus (Marsh.)) were conducted at Croton, Ohio, during 1947-48 and 
 1948-49, in which surface applications of dilute insecticide dusts were made 
 with a hand fertilizer spreader. DDT, benzene hexachloride, and chlordane 
 were tested in 1947-48. In 1948-49 the same materials and also parathion, 
 toxaphene, methoxychlor, and aldrin were used. 
 
 Results obtained from the 1947-48 tests indicated that both technical 
 benzene hexachloride at 1 1/4 pounds of the gamma isomer per acre and 
 chlordane at 5 pounds per acre, applied in either the fall or the spring, 
 gave excellent control of the clover root borer. DDT at 5 pounds per acre 
 was not effective. Data from plots receiving both a fall and a spring 
 treatment showed no advantage over a single fall or spring treatment. 
 
 Similar results were obtained in 1948-49. Aldrin at 2 pounds and 
 parathion at 5 pounds per acre, applied early in May, also gave excellent 
 control, but methoxychlor at 10 pounds, toxaphene at 5 pounds, and DDT 
 at 5 pounds per acre were ineffective. 
 
 :d samples taken in 1948 and 1949 showed that the treatment in- 
 creased the yields only slightly, if at all. However, the full impact of the 
 loss of seed due to clover root borer attack would not be evident in these 
 tests due to a lack of pollinators and also to poor stands associated with 
 prevalent clover diseases. 
 
 The root borer treatments also gave excellent control of nymphs of 
 
 meadow spittlebug ( Philaenus leucopthalmus (L.)). which have been 
 very numerous in red clover fields in Ohio for several seasons. All the 
 materials that were effective against the clover root borer as either a 
 fall or a spring treatment were effective against spittlebug nymphs. The 
 data indicate that these two important red clover pests may be controlled 
 by the san (lent. 
 
 ; ature Cit< d 
 
 ,,: D.S.. N.-wsome, L. D. , Gynsco, G., and Schwardt, H. H. 
 
 Lov( r POOl borer. Jour. Econ. Ent. 42: 315-318.