Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. 4 2 : Czrcular No. 920 September 1953 ¢ Washington, D. C. UNITED STATES DEPARTMENT OF AGRICULTURE Whe Hall Scale Eradication Project: By E. H. Fosen, (agent) agriculturist, Region iV, and A. W.CressMAn, entomologist, Division of Fruit Insect Investigations, Bureau of Entomology and Plant Quarantine, Agricultural Research Admin- istration, and H. M. Armirace, chief, Bureau of Entomology, California Department of Agriculture. CONTENTS Page Page HM GROMUCEIO Ma tts si eo eapel cies toe iE radicatiom propramiws i. ea aes 5) DISEHIDUCION kr ee ce ters Ds a Sutvcy andinspectiOns....cv8 5 Hostiplants;and injury: 02). Sle abreatment 2) aorta ee ee 9 Description of stages and habits....... Ay SUMMING sh acon Seas owe te ae aca 15 SeasonalelistOnye sc. eon Oe Aipiciterature cited aaa ets 16 INTRODUCTION The Hall scale CNelotaspis halli (Green)) was discovered in the United States in cue U.S, Plane Introduction Garden at Chico, Calif., by, C. F. Kinman in 1934. It was first found on Prunus bokhariansis and subsequently on many additional species and varieties of Prunus and Amygdalus. Upon discovery of the scale, host plants that had been shipped from the Plant Garden that season were located and destroyed. Inspection of many of the host plants shipped to various points in California from 1928 through 1933 gave negative results, and it was decided to attempt eradication of the infestation in the Plant Garden (Mackie 11).2 Many trees were pulled and burned. Treatment of the remainder included cutting back to scaffold branches, scraping the bark, painting with oil emulsion, fumigating with hydrocyanic acid gas, and applying a special tree paint (fig.1). Fumigation was at the rate of 2.5 ounces of more of sodium cyanide per 100 cubic feet 1 The work described in this circular was established as a Federal-State cooperative project by the U. S. Bureau of Entomology and Plant Quarantine and the California Department of Agriculture, under the respective supervision of D. L. Van Dine and the late D. B. Mackie. It was subsequently organized and directed by B. L. Boyden of the Bureau in cooperation with Mackie until 1945. Contributions of V. R. Jones, in charge of fumigation, H. W. Gray, in charge of inspection, and H. J. Crawford, in charge of biological studies, and the technical assistance of H.R. Yust and R. A. Fulton in developing fumigation procedure are acknowledged. The first four photographs were taken by Cliff Clower, of the California Department of Agri- culture, ‘ * Italic numbers in parentheses refer to literature cited, p. 16. 249715—53— eal 5 CIRCULAR 920, U. S. DEPT. OF AGRICULTURE Ficure 1.—Treatment of trees infested with the Hall scale in the Plant Introduction Garden, Chico, Calif., in 1935. for 1 hour under double untreated canvas or rubberized covers. Some scales survived this procedure, and treatment or removal of them was con- tinued until the infestation was thought to be eradicated. However, in an insect survey of the Chico atea in 1940, the scale was found again—in an almond orchard adjoining the Plant Garden, and later in the garden. As a result, a joint Federal-State project was organized in 1941 to determine the area infested and investigate the possibility of eradi- cation. This circular summarizes information on the biology and habits of the Hall scale and the progress made in determining the area of infesta- tion and eradicating the scale. DISTRIBUTION The Hall scale was described from Egypt by Green (8). Mackie C0) learned through correspondence that it was found in Turkey and Tripoli and that it was common over all lower Egypt. It is also recorded from Afghanistan (Archangelskaya 1), U. S.S. R. (Turkmenia, Uzbekistan, and Tadzhikistan) (Borchsenius 4), Greece (Koroneos 9), Iraq (Bodenheimer 2, 3), and Baluchistan.* Specimens from Syria, Iran, and Israel have also been identified by the U. S. Bureau of Entomology and Plant Quarantine. The place of origin and the time of its introduction into the United States are unknown. After the infestation was discovered near Chico, in Butte County, in- festations were found in Oroville and Davis, Calif. All the evidence indi- cates that the infestation in the Plant Introduction Garden at Chico was the source of the other infestations. Although there had been considerable movement of host plants out of the Plant Garden to other parts of California 3 Personal communication from A. M. Boyce, University of California Citrus Experiment Station, Riverside, Calif. Specimens identified by H. L. McKenzie, California Department of Agriculture, Bureau of Entomology. THE HALL SCALE ERADICATION PROJECT 3 and the United States before the original infestation was discovered, a subsequent survey has failed to show that they carried any infestation. Since the discovery of the scale, all hosts have been vacuum-fumigated before being permitted to leave the garden. HOST PLANTS AND INJURY The hosts on which the scale has been found in this country are limited to the genera Prunus and Amygdalus, and the shrub Spereae veztchiz. Pre- ferred hosts include almonds, peaches, nectarines, plums, and prunes (fig. 2,3). Pomegranate (Punica granatum) 1s recorded as a host in the literature Figure 3.—Hall scale on peaches, showing blotches caused by scales. 4 CIRCULAR 920, U. S. DEPT. OF AGRICULTURE (Archangelskaya 1), but has not been found infested in the United States even when adjacent to heavily infested trees. Additional hosts recently reported include Pyrus, Malus, Cydonia vulgaris, and Cerasus (Borchsenius 4). The scale is a potentially serious pest. In addition to its weakening effect on the tree, the insect’s tendency to migrate to and develop on the fruit may Cause severe injury to some fruits. The scale causes conspicuous blotches on peaches (fig. 3), nectarines, and plums. When the infestation at Davis was discovered, it was estimated that 25 percent of the peach crop was damaged even though the trees had been sprayed with oil the preceding winter. The hulls of almonds may become heavily infested, but no damage to the nuts has been discovered. Although every infestation was inten- sively treated as soon as discovered, feasible observations suggest that the most important injury may result from infestation on the fruit. DESCRIPTION OF STAGES AND HABITS The Hall scale is ovoviviparous. The oval, pale-yellow crawlers are about 0.23 by 0.12 mm. After a short period of activity, the crawlers settle, insert their mouth parts into the host tissue to feed, secrete a protec- tive waxy covering, and gradually increase in size. The females molt twice and the males three times. Only the adult males have wings. Mating takes place soon after the females have gone through the second molt. The cover of the adult female scale is elongate-oval, about 1.08 by 0.44 mm., and usually creamy tan with the orange exuvium of the second stage at one end. The body is a pale yellow. The male covering de- velops in the second instar as a narrow scale, with nearly parallel sides, thinner texture, and lighter color, whereas the female scale is more oval, denser, and darker. The male completes its development to winged adult beneath this narrow cover. The young scales settle on all parts of the host. Generally the males outnumber the females on foliage, fruit, and twigs of the current season's growth, but more females are present on other parts of the trees. Field observations indicate that the two sexes are present in nearly equal numbers. Many crawlers, especially the females, settle in protected places, such as deep crevices in wood, under loose bark, and under bud scales. This habit makes both inspection and control difficult. During the spring and summer there is also considerable movement from the trunk and larger branches to the current year’s twig growth, leaves, and fruit. For example, 1,812 scales have been found on 1 almond hull and 1,962 on a current-growth almond twig 22 inches long. Fruits of peaches, nectarines, and prunes have also become heavily infested. The reproductive capacity of the females could not be determined from field observations. The maximum number of ova and embryonic cells observed in a single female was 74. The total progeny might well exceed the number of ova seen at any one time. SEASONAL HISTORY During January the only live scales found are nongravid females. A few gravid stages have been found in February, and most of them are gravid THE HALL SCALE ERADICATION PROJECT 5) in April. The crawlers begin to emerge in April or late in March. A further chronology of field observations is as follows: Iya ets reap tre NG yee eam etre neta gs first molt INO) Sissi resco eens Ansar id late areas en males recognizable [eto Pe aie Sa WER cis lnc ES pue hak a ae eR en anette second molt of females; males emerged gjUlye2G Mpa nett Pert op, sini ete ele ke gravid females on current growth Te OU OTe The Peet es Sea aie a cee gee nearly spent females on current growth @ctoletal Gy wks eee hare wane Sek ase sees last crawlers and last males found; live scales in all stages present Wecember NOM ake ce cr cine eee last gravid females found Crawler emergence generally reaches a peak in May or June, before the summer sprays are applied. In the absence of a summer-oil spray, emer- gence might continue at a high rate throughout the summer. The finding of emerged males by June 24, gravid females by July 26, and nearly spent females by August 7, all on current season’s growth, shows that there is at least a partial second generation in the summer. ERADICATION PROGRAM When the eradication project was undertaken in 1941, the following program was adopted: (1) Repeated applications of oil sprays to reduce the scale population on known infested properties and decrease the danger of spread while other work was being carried on. (2) Survey of the Chico area to locate infestations resulting from movement of host plants from the Piant Garden. (@) Intensive inspection within 2 miles of known infested properties. This distance was tentatively set as the limit of natural spread. As information was developed, it was later reduced to 1 mile. (4) Location and inspection of host material shipped from the plant garden to points outside the Chico area before 1934, when a fumigation procedure for treatment of all hosts being sent out of the garden was established. (5) Removal of heavy growth along creeks running through infested properties to reveal and permit removal and destruction of host seedlings. (6) Field tests of oil sprays, both alone and with added toxicants, and of hydrocyanic acid gas fumigation, to develop an eradication treatment. As a result, an effective treatment con- sisting of fumigation with hydrocyanic acid gas under gastight tents was developed. The treatment program includes provision for the following: (a) A spring and an early fall spray of light medium oil applied each year beginning with the discovery of an infestation, and continuing to completion of the fumigation program, to suppress an infestation until fumigation can be started and to supplement fumigation during the subsequent treatment period. (b) Annual fumigations with hydrocyanic acid gas for 3 consecutive years after the last finding of live scales. (c) Several annual intensive inspections to check results of treatment after the final fumigation. SURVEY AND INSPECTION All properties in an irregular area approximately 15 miles long and 12 miles wide surrounding the city of Chico, containing approximately 800,000 host plants, mostly almonds, were scheduled for inspection. The area is isolated from other fruit-growing sections by grain, pasture, and open range land. The movement of infested plant material was considered to be the most likely means of spread to these properties. It was found that any material obtained from the Plant Garden was likely to be planted near houses or other buildings or along roadways 24971553 —2 6 CIRCULAR 920, U. S. DEPT. OF AGRICULTURE where it could be easily observed. Therefore, the first inspections were limited to host plants in yards and spot examination of other plants near buildings and roadways on properties outside the intensive-inspection zones. Every property within the area was inspected in this manner. The owner of the property was questioned to find out whether he had received Plant Garden material and if he had his property was scheduled for future reinspection. In reinspections, hosts from the Plant Garden, as well as adjacent hosts, were included. If the Plant Garden hosts had been removed, all host plants within approximately 50 feet of the former location were checked. If the owner did not have any information on the location of the host plants, every host on the property was examined. Two infested areas where scales were not found in the first inspection were located by reinspection of properties of recipients of suspected material. As inspection progressed, it was found that the build-up and spread of the scale were slow, that natural spread was limited to the immediate vicinity of infestations, and that any infestation found outside this restricted area would probably be due to movement of infested material from the garden. Therefore, the original plans with reference to inspection of properties near known infestations were modified. The probable area of natural spread was redefined to include the area within 4 mile of known infested properties. Within this area orchards adjacent to infestations were given a tree-to-tree inspection and at least one-fourth of the trees in other orchards were inspected. Inspections were made from the ground and from ladders, and were supplemented by microscopic examination in the laboratory of large numbers of randomly collected twigs. This pro- gram was carried out at least twice in much of the intensive inspection areas Until the discovery of a long-standing infestation near Bidwell Park in 1949, natural spread appeared to be limited to properties adjacent to pre- viously infested properties. In the Bidwell Park area infestation were found more than }4 mile from any other infestation. The intensive inspec- tion was then Sed to include the area within 1 mile of all known infestations. The intensity of inspection outside the \4-mile area previously inspected, varied with the degree of the earlier infestation and the time since the area had been put under treatment. In Chico and nearby towns every host plant was inspected. The U. S. Bureau of Plant Industry furnished a list of all shipments of host material from the Plant Garden made from 1928 to 1934. Shipments made during these 6 years were selected as representing a large sample of the material sent out. They contained material most likely to be infested, since the infestation could be expected to increase from the time of estab- lishment until discovery in 1934. All the material that could be located in the Pacific Coast and adjacent States and in the Gulf States was inspected with negative results. These regions were selected as the ones likely to be most favorable to the establishment of new infestations. The ento- mologists of the States concerned cooperated in this work, and some of the inspections were made entirely by State personnel. Inspections in Calli- fornia were made by County, State, and Federal employees. THE HALL SCALE ERADICATION PROJECT 7 OREGON BIOWELL eacn ea INFESTATION NE VAOA Figure 4.—Hall scale infestations in the United States, with enlargement of the Chico, Calif., areas Figure 4 shows the infested areas, all in California. The approximate numbers of host plants in these areas were as follows: Chico: WnitedaStates:PlancaintroductionsGarden tan 4 a le 15,000 NOHMSO Merny a eo erty eer ee ee, Conn See hot Wag aioe Se aamedar el tau Sie cures ee 3,600 IREW Ea ais arc Bena aspen ENRON lpn et BU Zee A SB Shee ae eR Oe ee eet 500 iGavel heat mentee aie wot MMM OO tee ea ete ag eaten nies Rc ne ene ee aU uae ape 15,400 Rersivalleas aera erik Coos heen ethan Oa Nn ae Ls, 900 (OF ROR aU MSs ee eT mae aS a ee aoe arch Rt oe ia Naa, a Pace 800 DAayiIShCatm DUS eee ete eam in crc re mr es wea Dc keene Vomda nine tere, 2,800 Most of the infestations were near Chico. At Oroville, about 20 miles from Chico, eight city blocks were infested. At Davis, approximately 100 miles south of Chico, in a University of California experimental planting, 1 As of December 1951, inspection not completed. S CIRCULAR 920, U. S. DEPT. OF AGRICULTURE about 15 acres were infested. A great deal of host material had been shipped from Davis to growers throughout the State, but no infested plants origi- nating from this infestation were found outside the Davis orchard and nursery. No scales were found in the University’s orchard at Winters, although much material was interchanged between Davis and Winters. All the infestations appear to have originated from movements of infested host material from the Plant Garden and all except the Davis infestation probably date back to 1930 or before. Two types of spread within the infested area are illustrated in figure 5. In the Johnson area (fig. 5, 4) the infestation probably originated with the \\" \