S.K. Braman and A.F. Pendley Entomology Dept., University of Georgia, Griffin, GA ABSTRACT

Transcription

1 Internatinal Turfgrass Sciety Research Jurnal 7. R.N. Carrw, N.E. Christians, R.C. Shearman (Eds.). Intertec Publishing Crp., Overland Park, Kansas Chapter 49 Grwth, Survival, and Damage Relatinships f White Grubs In Bermudagrass Vs. Tall Fescue S.K. Braman and A.F. Pendley Entmlgy Dept., University f Gergia, Griffin, GA ABSTRACT Third instar grwth and survival, and the effect f larval density f the Japanese beetle, Ppillia japnica Newman and the suthern masked chafer, Cyclcephala lurida (Olivier) were evaluated n Tifway bermudagrass, Cyndn dactyl n (L.) and KY-31 tall fescue, Festuca arundinacea Schreb. in a three- year field study. Winter survival was smetimes enhanced in bermudagrass plts. Larval weight gain, hwever, was mre ften favred by feeding n fescue. Percent survival after 8-9 mnths was greatest when initial infestatin levels were 3 per 0.02 m 2 micrplt r fewer. Average survival ranged frm 10.8 t 76%, depending upn turfgrass species, white grub species, and year f study. Little reductin in whle plant dry weight r in peridic tp grwth measurements was bserved in these irrigated plts. INTRODUCTION Managed turfgrasses are subject t infestatin and damage by a variety f pests. Amng the mst injurius are the larval stage f several species f scarabaeid beetles, cmmnly referred t as white grubs (Tashir 1987, Ptter & Braman 1991). At least ten species f grubs cmmnly damage turf directly by feeding n the rts r as a result f burrwing activity. Japanese beetle, Ppillia japnica Newman and suthern masked chafer, Cyclcephala lurida (Olivier) are widely distributed, serius pests f turfgrass, rnamentals, and agrnmic crps (Tashir 1987). Seasnal ppulatin dynamics, influence f misture n emergence, survival and vipsitin, use f phermnes in management, and behaviral eclgy n these and ther white grub species have been subjects f extensive study (e.g., Ptter 1980, 1981, Regniere et al 1981, Villani & wright 1988). sil inhabiting turf pests are amng the mst difficult t manage. Cntributing factrs include lack f practical and reliable sampling and mnitring strategies, the lack f understanding f interactins between pests, cntrl tactics and the envirnment, and the difficulty in establishing meaningful actin threshlds (Villani & Wright 1990). The influence f larval feeding by P. japnica and C. lurida has been studied n bluegrass turf (Ladd & Buriff 1979, Ptter 1982). Turf receiving regular irrigatin and adequate rainfall was fund t mitigate negative effects f grub infestatins as high as 24 per 0.lm 2 feeding fr 4 weeks (Ptter 1982). Yields frm pts maintained at 90% f field capacity were 34-55% greater than yields frm pts with sil misture maintained at 60% when infested with third stage P. japnica larvae. Research reprted here was undertaken t further define the influence f these tw white grub species n KY-31 tall fescue, Festuca arundinacea Schreb. and Tifway bermudagrass, Cyndn dactyl n (L.) Pers. under cnditins f adequate misture and t determine mid t late seasn grwth, survival, and cmparative ptential fr damage f P. japnica and C. lurida. 370

2 MATERIALS AND METHODS Turfgrass cres 15 cm in diameter were remved each year (89-91) during May using a glf curse type cup cutter and allwed t re-establish in 15 cm diameter PVC tubes (0.02 m' surface) buried in the grund a depth f 30.5 cm. Masked chafer larvae cllected frm a fescue hme lawn in Spalding C., Ga were used t infest the tubes n 6 Octber, During 1990 and 1991 suthern masked chafers cllected at light traps and Japanese beetles cllected in attractant traps were caged n 1.5 m diameter children's wading pls filled with sil and seeded with KY-31 tall fescue the previus fall. Third instar grubs were harvested frm the pls and used t infest the tubes n 1 September 1990 and 9 September Screens in the bttm f the tubes permitted drainage but prevented escape f larvae. Each treatment (tube cntaining each density f grubs) was replicated eight times in a cmpletely randmized design during each year. Larvae were weighed prir t infestatin. Treatments in 1989 were 0, 1, 2, 3, 4, 5, r 6 C. lurida per 0.02 ~ area. Infestatin levels during 1990 and 1991 were 0, 3, 9, r 15 P. japnica r 0, 3, 9, 15, r 21 C. lurida. The sil was a cecil sandy lam. Micrplts were irrigated as needed during the re-establishment phase. After infestatin, fescue and bermudagrass plts were irrigated with 0.6 cm and 0.3 cm water, respectively, in the evenings during September and Octber. Rain guards n the irrigatin system turned the irrigatin ff when there was mre than 0.3 cm precipitatin per day. Fescue and bermudagrass plts were clipped t 5 cm and 2.5 cm, respectively, prir t infestatin. Regrwth during the experimental interval was measured n 1 March 1990 by recrding height abve the surface. Fescue clippings f grwth greater than 0.5 cm were ven dried at 48 C fr 4 days and weighed. The number f green shts per 1.3 cm 2 als was measured n 28 February Plts were destructively sampled n 27 April Larvae were recvered and weighed. Sil was washed frm the rts, plants were ven dried fr 7 days, and whle plant dry weights were recrded. During tp grwth was measured n 17 Octber, 28 Nvember, 12 February, and 20 March befre final, whle plant samples were taken n 1 May, Larvae were again recvered and weighed. Tp grwth measurements during the final year f study were btained n 9 Octber, 5 Nvember, 6 December, 1991, 6 January, 6 February, and 6 March prir t harvest n 6 April Grwth and survival f each grub species in fescue vs bermudagrass were cmpared using Students t-test. Grass tp grwth (height and weight), and whle plant dry weights were cmpared within a grass species using the SAS GLM prcedure (SAS 1985). Mean separatin was achieved using a least significant difference test (Skal and Rhlf 1981). RESULTS Larval survival varied with turfgrass species, white grub species, and year f study (Table 1). Table 1. Survival and weight gain f suthern masked chafers (SMC) and Japanese beetles (JB) n tw grass species. Year Grub species Tall fescue x + SE x + SE % sur~ival wat aain (mal _ BermudagEass x + SE x + SE % sur;ival wat aain (mal SMC 26.4j: 5.4* j: 13.9* 76.0 j: j: SMC JB 10.8j: j: j: 12.4* j: j: j: j: j: SMC JB 38.6j:l j:l j: j: 13.3* j: j: j: j: 7.2 P < 0.05 Cmparisns f survival r weight gain between grass species fr each grub species. 371

3 Survival ranged frm 10.8% (C. lurida, fescue, 1990/91) t 76% (C. lurida, bermudagrass, 1989/90). Survival was significantly (P < 0.05) greater fr bth grub species when bermudagrass was the turfgrass hst during 1989/90. During 1990/1991 and 1991/92, survival n bermudagrass was nt significantly greater than n fescue (P> 0.05). Average larval weight gain during the trial perid was generally greater when grubs were caged n fescue (P < 0.05). Significant reductins in final whle plant dry weights were detected nly when the dry weights were cmpared with final infestatin levels f grubs recvered frm plts during 1989/1990 (Table 2). Table 2. Influence f SMC larval feeding n seasn-lng plant grwth during 1989 as measured by initial infestatin level (IlL) and final number f larvae recvered (FNL) per 0.02 m 2 x + SE ttal plant drv weiaht (aml Tall fescue Bermudagrass N. f larvae IlL FNL* IlL FNL ~ ~ ~ ~ ! ! ! ! ~ ~ ~ ~ ! ~ ! ~ ! ! ! ~ ~ ~ ~ ! !.10.1 * P < 0.05 N density related reductins in plant final dry weights were detected during the subsequent tw years (Table 3). Clipping heights and dry weights measured n 12 ccasins during three years in these irrigated plts never revealed a grub density related reductin in grwth. The rate at which winter drmant bermudagrass resumed grwing as measured by number f green shts per cm2 was nt significantly related t infestatin level (P> 0.05). Density related damage might have been much mre evident had the entire larval feeding perid been measured r had drught stress been induced. Table 3. Influence f larval feeding n seasn-lng plant grwth during 1990 and 1991 by Suther masked chafer (SMC) and Japanese beetle (JB) N. f larvae x + SE ttal plant drv weiaht (aml Tall fescue Bermudagrass SMC JB SMC JB i: l4.4~ ~ :!: ~ ! ~ :t ~ ! ! ! ~ :t ~ ! ~ ~

4 Larval survival f bth species was significantly reduced by larval densities f mre than 3 grubs per micrplt during 1991/92 (P< 0.05) (Figure 1). Significant reductins in survival related t initial grub density als were determined during 1989/90 fr C. lurida n fescue (P= 0.02). The fungal pathgen Metarhizium anispliae was bserved in larval cadavers recvered frm micrplts during 1991/1992 and was likely a cntributry factr in the density related mrtality experienced during this study. CONCLUSIONS The tw grub species studied respnded differently in terms f grwth and survival depending upn turfgrass hst species in this field evaluatin. In general Tifway bermudagrass enhanced larval survival, while KY-31 tall fescue favred third instar larval grwth. Pssibly greater larval weights wuld result in larger adults with greater fecundity althugh this was nt tested. Results f this study indicate that turf irrigated during critical perids can tlerate grub densities well in excess f established threshlds. REFERENCES CITED Ladd, T. L., Jr. and C. R. Buriff Japanese beetle: influence f larval feeding n bluegrass yields at tw levels f misture. J. Ecn. Entml. 72: Ptter, D. A Flight activity and sex attractin f nrthern and suthern masked chafers in Kentucky turfgrass. Ann. Entml. Sc. Am. 73: Ptter, D. A Seasnal emergence and flight f nrthern and suthern masked chafers in relatin t air and sil temperature and rainfall patterns. Envirn. Entml. 10: Ptter, D. A Influence f feeding by grubs f the suthern masked chafer n quality and yield f Kentucky bluegrass. J. Ecn Entml. 75: Ptter, D. A. and S. K. Braman Eclgy and management f turfgrass insects. Ann. Rev. Entml. 36: Regniere, J., R. L. Rabb, and R. E. Stinner Pplllia japnica: Effect f sil misture and texture n survival and develpment f eggs and first instar grubs. Envirn. Entml. 10; SAS Institute Inc SAS User's Guide: Statistics, Versin 5 Editin. Cary, NC: 956 pp. Skal, R. R. and F. J. Rhlf Bimetry. Secnd editin. W. H. Freeman and C. San Francisc. 859 pp. Tashir, H Turfgrass insects f the United states and Canada. Crnell University Press. Ithaca, N.Y. 474 pp. Villani, M. G. and R. J. Wright Use f radigraphy in behaviral studies f turfgrass- infesting scarab grub species (Cleptera: Scarabaeidae). Bull. Entml. Sc. Am. 34: Villani, M. J. and R. J. Wright Envirnmental cnsideratins in sil insect pest management. Tn D. Pimentel [ed] CRC Handbk f pest management in agriculture. CRC Press, Inc. pp

5 C Bermudagrass 0-0 Fescue > > 60 L ::J U) 20 > 30 L 10 ~ / /1991 if2 100 Q) Initial larval density Fig. 1. Influence f initial infestatin level n larval survival in KY- 31 fescue and Tifway bermudagrass during 1989, 1990, and