Soft Brown Scale on Citrus abnormal increase of scale population in groves treated with parathion investigated in survey

H. S. Elmer, W. H. Ewart, and G. E. Carman

Not all commercial groves treated of 23.9 scales per leaf seven months after with parathion develop abnormally high the last treatment of parathion. However, populations of soft brown scale but where 14 months after the last treatment para- populations do increase they usually are sites and predators had eliminated the extensive and have definite characteris- soft brown scale population in this par- tics in comparison to populations found ticular grove. in groves not treated with parathion. Following experimental applications of parathion for the control of yellow Test Treatments scale and citricola scale in certain groves Spray applications of parathion at the in the San Joaquin Valley, the soft brown rate of 100 to 200 gallons per acre with scale became a major pest in 1947. Since Photograph by Mcrfa McD. lohnron spray duster equipment for the control Appearonce of soft brown scale on an orange then abnormally high populations have leaf. Darker scole at right is an older specimen. of citricola scale also caused an increase been observed in other groves treated in soft brown scale populations. These with parathion in the San Joaquin Val- populations, however, generally were less ley, in the Sacramento Valley, and in control of citricola scale, black scale, extensive than those in groves treated southern California. California red scale, or yellow scale. with thorough coverage applications. This survey disclosed a great amount Larger populations of soft brown scale of variability in soft brown scale popula- occurred in and persisted longer in plots Resistance to Parathion tions in different plots and groves follow- treated with parathion without oil than Preliminary investigations indicated ing parathion treatments. In certain in plots treated with petroleum oil sprays that these increases were the result of a groves, however, there was a relationship to which parathion had been added. There striking resistance of this species to para- between the size of the population and were, however, usually more soft brown thion, coupled with the susceptibility of the dosage or number and timing of para- scales in plots treated with parathion- its parasites to this compound and their thion treatments. petroleum oil sprays than in untreated consequent elimination from treated In one grove, plots had been treated plots or plots treated with oil alone. groves for relatively long periods. in 1947 with dosages of 1, l%, 2, 2%, Plots treated with experimental insec- In untreated groves the soft brown and 3 pounds of 25% parathion wettable ticides other than parathion were closely scale is normally found in colonies re- powder per 100 gallons of water applied watched throughout the survey for any stricted to occasional branches which are at the rate of 3,000 gallons per acre. One abnormal increases of this scale. almost always attended by ants. In para- year later the soft brown scale popula- Other organic phosphate compounds thion-treated groves soft brown scale is tion in these plots averaged 0.3, 1.2, 2.8, that caused increases in populations of found throughout the trees on the leaves 6.1 and 3.1 scales per leaf, respectively. soft brown scale were 0,O-dimethyl S- and small branches largely unattended The plots treated with the higher dosages (2-oxo-2-uredioethyl) dithiophosphate- by ants. of parathion were not entirely cleared up Compound 3901 ;S-carbamylmethyl0,O- Soft brown scale is found throughout by parasites one year and four months dimethyl dithiophosphate-Compound the commercial citrus producing areas after treatment. 3869; para-oxon ;and ethylp-nitrophenyl of California, but has normally been a Three plots in another grove were thionobenzenephosphonate-EPN. minor pest because of very effective para- treated in 1949 with 1, l$$,and 2 pounds Para-oxon-treated plots, in one grove, sites and predators. of 25% parathion wettable powder per had higher populations of this scale than Heavy populations of this scale weaken 100 gallons applied at the rate of 3,000 did plots treated with similar dosages of the trees by removing large quantities of gallons per acre had an average of 0.2, the other organic phosphates, including plant sap and leaving large deposits of 0.1 and 0.4 scales per leaf, respectively, parathion. Parathion ranked second, fol- honeydew, which become blackened with two months after treatment. The popula- lowed in order by EPN, Compound 3901. sooty mold fungus and interfere with the tions were entirely cleaned up in all three and Com ound 3869. These last two com- normal functions of the leaves. This type plots four months after treatment by pounds s K owed but slight increases in the of injury is similar to that caused by parasites and predators that were able to population over untreated plots. Dieldrin, citricola scale or black scale. move back into the grove. aldrin, rotenone, DDT, TDE, methoxy- Other plots and groves showing similar chlor, and DFDT treated plots in this abnormal populations of soft brown scale grove had no significant increases in the Survey failed to clean up only when additional population of soft brown scale. To develop information on the relation treatments of parathion were applied be- The survey was continued into 1951 between parathion treatments and in- fore the parasite and predator popula- and differences were observed when com- creases in soft brown scale populations, tions had a chance to move back into the pared with the 1949 and 1950 survey. a survey was made in 1949 and 1950 in grove. Groves treated with high dosages of para- approximately 100 experimental plots One plot treated six times over a pe- thion in 1951 did develop high popula- and in 22 commercially treated groves in riod of two years-in 1948 and 1949- tions of soft brown scale immediately which parathion had been applied for the had an extremely high population count Continued on page 13

10 CALIFORNIA AGRICULTURE, JANUARY, 1952 SPRAY the semicoriceritrate and concentrate insecticides are necessary, applied at in- methods of application are comparable tervals of from four to six weeks. The Text continued from page 11 or equal. concentration of DDD or DDT in the dust should be 5% and the dusts applied at 6. Spray chemical. Fumigant types Arthur D. Borden is Lecturer in Entomology, such as TEPP and parathion may require University of California College of Agriculture, the rate of from 30 to 35 pounds per acre less gallonage per acre in aphid control. Berkeley. per application. Best results are assured where the dusts are evenly and thoroughly Oil emulsions and lime sulphur must be The above progress report is based on Re- applied at lower concentrations and gal- search Project No. 806. applied. Where obstacles-such as trees, lonage to avoid excess deposits. buildings, power lines, oil derricks-in- 7. Condition of bark at time of appli- terfere with airplane applications, sup- cation. Dry bark absorbs more spray TOMATO plemental measures should be used to liquid and requires a higher gallonage. treat any areas missed, If this is riot done, 8. Atmospheric conditions. Warm, dry Continued from page 7 the harvested crop may contain annoying air increases evaporation and requires earworm, tomato pinworm, and the amounts of infested fruit, particularly in larger gallonages to wet the trees ade- larvae of the potato tuber moth. In Cen- the late shipping crop from the southern quately. tral California it is seldom necessary to San Joaquin Valley. Failure to obtain 9. Amount of wind. An increased gal- initiate control against these pests before highly satisfactory control should not be lonage is generally required even if a early July. In the warmer portions of the blamed at present upon the insecticide light wind is blowing. San Joaquin Valley, it may be necessary but upon the application. 10. Insects to be controlled. Bark in- to start treatments in May or June. In recent years a leafminer occasion- festations of scale insects are more satis- Sulfur is the principal material used ally has caused serious defoliation of to- factorily controlled by bulk sprays or to control the tomato mite, while DDD mato plants. At first, some of the newer increased applied gallonage. and DDT are the chief insecticides used insecticides-such as DDD and DDT- In general, the applied gallonage pe.r against the several species of caterpillars. were held responsible for an increase in acre required for fruit trees with the semi- Sulfur for the control of the tomato mite the population of the leafminer. After in- concentrate and concentrate methods of can be used in combination with the in- vestigation it appears that serious infes- application may be expressed as the fol- secticide selected for the control of cater- tations by the leafminer are more lowing fractions of what is required in pillars. In such cases the concentration dependent upon natural surroundirlgs and the hulk application method : of sulfur should not be less than 50?, conditions than upon insecticides used. Gollonoge The insecticides used in the tomato in- required and-for the first application-best con- trol of the mite will be insured if the sect control program will not result in a Contentra- \k,!r:i residue problem if used as recornmended tion (in sulfur content is 75%. In most cases, multiples require- where it appears that there is poor con- and if the fruit is washed or wiped care- of standard ~~~~$~ fully before being marketed. dosage 1X) ap80. lira- trol, it is because applications were made method) too late;.poor coverage was obtained es- A. E. Michelbacher is Associate Professor of pecially in the vicinity of aerial obstruc- Entomology, University of California College of 1x 4/5 tions such as buildings, trees, or power Agriculture, Berkeley. Semiconcentrate 2X 2/5 lines; insufficient material; or faulty 0.G. Bacon is Assistant Professor of Entomol. applications 3x 3/10 ogy, University of California College of Agri- equipment. To the present time there has culture, Berkeley. 4x 1/5 been no positive indications that a strain W. W. Middlekauff is Associate Professor of of mite resistant to sulfur is being selected Entomology, University of California College of 6X 1 /a from the population. Agriculture, Berkeley. Concentrate ax 1/10 applications ox In general if the control of the mites 1/12 has been satisfactory and no evidence of them can be found by the first part of SCALE The table on page 12 gives the gallon- September, sulfur can be omitted from Continued from page 10 age and amount of material to be applied later applications of insecticides intended per acre with the various concentrations for caterpillar control. after the application but such populations of spray chemicals, as used in bulk, semi- DDT is not nearly so effective as DDD did not persist so long as in the previous concentrate and concentrate methods of for the control of the tomato horn- two years. application. worm, Protoparce sexla. Therefore, in the . Multiple applications of parathion in The gallonage as applied by the bulk warmer interior valleys where this cater- 1951 were no more serious in this respect method-being most familiar to grow- pillar is likely to be present in destructive than single treatments were in 1949 and ers-is used as a base in determining the numbers, DDD is the recommended insec- 1950. One possible explanation is that data. ticide for the first two applications. How- the increased populations of this scale in The variance in planting and number ever, DDD is not effective against flea 1948 and 1949 because of parathion treat- of trees per acre is covered in column one. beetles. A switch to DDT for a final appli- ments followed unusually cold winters The variance in tree size is indicated cation is frequently desirable as flea which may have reduced the number of in column two by the number of applied beetles may appear in destructive num- parasites to much lower levels than the gallons per tree in the bulk method. bers in tomato fields in late summer and milder winter in 1950-51. The variance in concentration of the early fall. By this time hornworms no H. S. Elmer is Assistant Specialist in En- three methods is indicated in columns longer present a problem, and the impor- tomology, University of California College o/ three to 10 by the multiples of lX, the tant caterpillars likely to be present in- Agriculture, Riverside. standard dosage. clude the corn earworm, beet armyworm, 117. H. Ewart is Assistant Entomologist, Uni- The reduction in the amount of ma- tomato pinworm and the potato tuber versity of California College of Agriculture, Riverside. terial applied per acre by the semicon- moth. Against these pests both DDT and G. E. Carman is Associate Entomologist, Uni- centrate and concentrate methods of DDD are highly effective. versity of California College of Agriculture, application does not exceed 2074 of that For an effective control of the tomato Riverside. as applied by the bulk method. mite and the several species of caterpil- The above progress report is based on Re- The amounts of material applied by lars, usually two to three applications of search Project No. 1416.

CALIFORNIA AGRICULTURE, JANUARY, 1952 13