Proc. Fla. State Hort. Soc. 93:115-120. 1980.

ECOLOGICAL OBSERVATIONS ON TWO THAT TRANSMIT THE PIERCE'S DISEASE BACTERIUM1

W. C. Adlerz Florida to North Carolina, and west to Arkansas and University of Florida, IFAS, eastern Texas (11, 12). It also occurs in Mexico. O. nigricans Agricultural Research Center, is distributed throughout peninsular Florida to- an area P. O. Box 388, Leesburg, FL 32748 in northern Florida where it approaches the southern-most distribution of orbona (F), (11, 12). There Additional index words. Oncometopia nigricans (Walker, may be a third undescribed species in a geographic zone Homalodisca coagulata (Say), , citrus blight. between the two (12). O. nigricans cannot be distinguished from O. orbona by external morphological characters. Turner and Pollard (11) listed 11 breeding and 62 Abstract. Oncometopia nigricans (Walker) and Homalo feeding host plants for H. coagulata in central Georgia and disca coagulata (Say) 2 known vectors of Pierce's Disease 18 breeding and 47 feeding host plants for O. orbona. (PD) winter as adults on perennial plants in central Florida. Similar host lists for O. nigricans have not been published. In spring many over-wintering leafhoppers leave winter All these species are primarily southern and feed widely hosts and disperse to spring-summer hosts as the plants on woody and herbaceous plants (1, 11). become suitable foroviposition. In all, O. nigricans adults Ecological studies of O. nigricans and H. coagulata in were observed on 63 hosts and nymphs on 41; H. coagulata cluding host plants, breeding habits, and inter-plant move adults were observed on 46 hosts and nymphs on 33. Host ments were undertaken with 2 main purposes in mind. plants were both woody and herbaceous. Four O. nigricans First, to identify plants that would be most useful in studies host plants and 5 H. coagulata host plants were identified of alternate hosts of the PD bacterium in Florida. Second, asespecially important in the seasonal development of to relate interplant movements of leafhoppers to what is populations and are suggested as candidate plants for known about the seasonal buildup of RLB in plants and study as PD bacterial hosts in Florida. Dispersals after the the occurrence of natural infectivity in leafhoppers. Interest first and second generations were in April-May and July for in both PD and CB led us to include cultivated grapevines, O. nigricans, and June and August for H. coagulata. These weeds in citrus plantings, and citrus itself in the surveys. times correlate with what is known about seasonal natural infectavity of leafhoppers which begins in late April, in Materials and Methods creases through July, and continues through the fall. The relationship of Pierce's disease to citrus blight is discussed. Four observation sites were selected that had a wide variety of weeds and some wild Yitis sp. bordering citrus Rickettsia-like bacteria (RLB) causing several diseases plantings. Four sites were selected especially for observa of woody and herbaceous plants are transmitted by leaf tionof wild 'Bullace' grape (V. munsoniana Simpson, hoppers of the subfamily Cicadellinae (4, 9). 'Bullace' special in Fig. 1). Four sites were selected es Pierce's disease (PD) is an RLB-incited disease that pecially for observation of leafhoppers on black cherry limits grape culture in Florida (10). It has been trans (Primus seroiina Ehrk.) in the winter. Other weeds were mitted by leafhoppers of all species of the subfamily included in observations at 'Bullace' and cherry sites. Cicadellinae tested as a vectors (9) including 2 species The citrus and 'Bullace' sites were visited weekly for 2 that breed on grapevines in Florida: Oncometopia nigricans years beginning January 1978. Cherry sites were visited (Walker) and Homalodisca coagulata (Say) (1). Neither of from fall, after populations declined in other these have approved common names, although, leaf areas, until the leafhoppers left the trees in the spring. hoppers in the subfamily Cicadellinae are commonly called At all sites, 2 observers walked established routes, counting sharpshooters, and O. nigricans and H. coagulata are insects on available weeds. Additional leafhopper hosts in locally called the blue and brown sharpshooters, respectively. the Leesburg area were identified during surveys in June PD is also transmitted by spittlebugs, family Cercopidae (9). 1978. Adlerz and Hopkins published information on the Citrus blight (CB), or young tree decline, is a major relative abundance of these insects on cultivated grapevine deterrent to citrus production in parts of Florida (3). Due during part of the study period (1). to certain similarities in the symptoms of PD of grapevines and CB of citrus and with the knowledge that the PD Results vectors O. nigricans and H. coagulata are common on both plants, we considered the possibility of an RLB (PD) O. nigricans etiology for CB. To test this, we fed leafhoppers free of Winter hosts. O. nigricans winters in the adult stage on PD bacteria on CB affected citrus (Citrus sinensis Osbeck, a number of perennial hosts (Fig. 1, 2). Adults are active 'Valencia') in the field and they subsequently transmitted in warm weather, feeding and making short local flights. the RLB of PD to grapevine (5). The possibility of an Insects inactivated by cold weather often drop to the association between PD and CB was strengthened when ground under host plants.Insects revived by increasing rough lemon (Citrus jambhiri L.), the rootstock most as temperature during the day resume activities on plants. sociated with CB occurrence, exhibited dieback symptoms Usually leafhoppers are most abundant on American elder after inoculation with the RLB of PD (7). (Sambucus canadensis L.), blackberry, (Rubus sp.), eastern Although natural transmission of CB by leafhoppers baccharis (Baccharis halimifolia L.), and black cherry. has not been confirmed, some epidemiological studies have During the mild winter of 1979 adults were able to survive been completed on the transmissionof PD in Florida by on lantana (Lantana camara L.), and 'Bullace' grapevines, O. nigricans and H. coagulata (1). and they were common on citrus. Copulatory activity and H. coagulata occurs in the eastern United States from egg masses were observed on American elder in January, 1979, but no nymphs were observed on winter hosts in iFlorida Agricultural Experiment Stations Journal Series No. 2782. January or February during either year.

Proc. Fla. State Hort. Soc. 93: 1980. 115

aceae: American elder; 3) Ghenopodiaceae: mexicantea; 4) State Hort. Soc. 66:33-37. Malvaceae: ceasarweed (Urena lobata L.), teaweeds (Sida 4. Hopkins, D. L. 1977. Diseases caused by leafhopper-borne, rickettsia- likc bacteria. Ann. Rev. Phytopathol. 17:277-294. sp.); 5) Onagraceae: primrosewillow (Ludioigia peruviana 5. Hopkins, 1). L., W. C. Adlerz, and F. W. Bistlinc. 1978. Pierce's (L.) Hara); 6) Phytolaccaceae: common pokeweed, 7) disease bacterium occurs in citrus trees affected with blight (Young Rosaceae: blackberry; 8) Rutaceae: citrus; 9) Verbenaceae: tree decline). Plant Dis. Replr. 62:442-445. lantana. Although wild grape may be the main source of 6. . 1979. Seasonal concentrations of bacterial plugs in grapevines severely infected with the Pierce's disease bacterium. PD bacteria, any plants, especially perennials, are po Phytopathology 69:528 (Abstr.). tentially important RLB hosts. 7. — and W. C. Adlerz. 1980. Pierce's disease bacterium causes Studies on citrus could be especially significant since a disease of rough lemon citrus. Phytopathology 70:568 Abst. RLB causing PD have been transmitted from citrus to 8. Purcell. A. H. 1976. Seasonal changes in host plant preference of the blue-green sharpshooter Hordnia circellata. The Pan-Pacific grapevine (5), citrus inoculated with PD bacterium de Entomologist 52:33-37. velops decline symptoms (7), and CB is presently the most 9. . 1979. Leafhopper vectors of xylem-borne plant patho serious disease of citrus. gens. In: Leafhopper vectors and plant disease agents. Maramorosch, K. and K. F. Harris Eds., pp 603-625. Academic Press. Literature Cited 10. Stoner, W. N., L. H. Stover, and G. K. Parris. 1951. Field and laboratory investigations indicate grape degeneration in Florida is 1. Adlerz, W. C. and D. L. Hopkins. 1979. Natural infectivity of two due to Pierce's disease virus infection. Plant Dis. Reptr. 35:341-344. sharpshooter vectors of Pierce's disease of grape in Florida. /. Econ. 11. Turner, W. F. and H. N. Pollard. 1959. Life histories and behavior Entomol. 72:916-919. of five vectors of phony peach disease. USDA Tech. Bull No. 2. Ball, J. C. 1979. Seasonal patterns of activity of adult leaf hopper 1188, 28 pp. vectors of phony peach disease in north Florida. Environ. Entomol. 12. Young, D. A. 1968. Taxonomic study of the Cicadellinae (Homop- 8:686-689. tera: Cicadellinae). Part 1. Proconiini. US National Museum Bull 3. Childs, J. F. L. 1953. Observations on citrus blight. Proc. Florida 261.

Proc. Fla. State Hort. Soc. 93:120-124. 1980.

FLORIDA GRAPES: THE NEXT DECADE

R. P. Bates period. It is, therefore, instructive to describe where the University of Florida, I FAS, industry came from and how it will develop and contribute Food Science and Hitman Nutrition Department, to Florida agriculture over the next 10 years. Gainesville, Florida 32611 Looking Back J. A. MORTENSEN University of Florida, IFAS, Except for the "Vineland" label which the Norsemen P. O. Box 388, Leesburg, Florida 32748 gave to Northeast North America about 1,000 years ago, the first recorded reference to grapes in the New World T. E. Crocker was from Spanish Florida in 1565 (17). From that time University of Florida, I FAS, on inhabitants of Florida have been intrigued by the crop Fruit Crops Department, and consistently attempted to produce grapes and make Gainesville, Florida 32611 wine (Table 1). These efforts have faced many problems over the Abstract. Grapes in Florida are receiving much greater centuries, and it is a tribute to horticulturists in the state attention than current planted acreage and economic ac that grapes are successfully grown. A few hundred acres tivity would suggest. Reasons for this optimism are a 4- of Vitis labrusca were reported in the early 1890's, but the decade breeding effort which is overcoming very serious vines lacked vitality and longevity and the effort failed disease problems and producing higher quality, more versa (23). Grape acreage increased remarkably in the 1920's, and tile cultivars with improved fresh, processed juice and wine 4 to 5 thousand acres existed as of 1926 (19). Most plant characteristics; progressive, enthusiastic grape growers; a ings were Munson hybrids—'Extra' (Florida Beacon), 'Car sympathetic state legislature and a long-term commitment men', 'R. W. Munson' and 'Armalaga' and were devoted by the Florida Grape Growers Association and the state, to fresh markets locally and in the Northeast. regional and national agricultural research establishment. In the late 1920's disaster struck again in 3 forms- The 1970 decade has resulted in progress with both bunch disease, depression and the fruit fly eradication program, (Euvitis) and muscadine (V. rotundifolia) grapes in the areas disease being by far the most devastating. The Munson of breeding, culture and processing. For the well-being of cultivars were plagued by short vine life (,~10 years); sus the grape industry, it is essential that these efforts be in ceptibility to rot and diseases associated with a hot, humid creased during the 1980's and coupled with greater atten climate; high cultivation and marketing costs; and weak tion to fruit quality and fresh, processed and wine market markets. Vine degeneration, later identified as Pierce's ing. Grape development priorities of the 1980's will be dis disease, and the Mediterranean fruit fly eradication program cussed in terms of desirable, achievable goals for 1990. effectively curtailed Florida plantings and resulted in a dramatic decrease in acreage, completely negating the com Of the 38 U. S. states which lay claim to a grape industry, mercial potential of Florida grapes for several decades (21). Florida probably ranks about 19th in acreage (1). But there is promise of greatly increased future production. The Turning the Corner decade of the 80's represents a very critical developmental Fortunately, during and subsequent to the grape boom iFlorida Agricultural Experiment Stations Journal Series No. 2672. of the 1920's the seeds of future expansion were being

120 Proc. Fla. State Hort. Soc. 93: 1980.