250 Fettig et al.: Effectiveness of Permethrin Plus-C and Carbaryl controls died from D. brevicomis attack (Shea et al. 1984). During the initial field season, 6.7% of Masterline-treated P. ponderosa died from bark beetle attack, whereas 53.0% mor- tality was observed in the untreated controls (Table 1). If two additional control trees had died, bark beetle pressure would have been sufficient to make definitive estimates of efficacy (Shea et al. 1984), and we would have concluded that both Masterline and Sevin SL were efficacious during the first field season. In 2005, only 3.6% of Masterline-treated trees died, whereas 40% mortality was observed in the untreated control (Table 1). No Sevin SL-treated trees died during the experiment. Montana: D. ponderosae and P. contorta In 2004 and 2005, beetle pressure was sufficient to ad- equately challenge these treatments (Shea et al. 1984). Mas- terline provided one field season of efficacy (6.7% mortal- ity), but in 2005, a significant number of Masterline-treated trees died from D. ponderosae attacks (58.5% mortality) (Table 2). Sevin SL was efficacious during both field sea- sons with 0% and 3.3% mortality observed in 2004 and 2005, respectively. Bark beetle pressure was extremely heavy dur- ing this evaluation as indicated by the mortality levels re- ported for the untreated controls (Table 2). Arizona: I. confusus and P. edulis In 2004 and 2005, beetle pressure was insufficient to ad- equately challenge the treatments because <60% of untreated controls died from I. confusus attack (Shea et al. 1984). In 2004, 4.2% of Masterline-treated P. edulis died from bark beetle attack, whereas 20.8% mortality was observed in the untreated control (Table 3). During the second field season, 4.3% of Masterline-treated P. edulis died from bark beetle attack, but only 5.3% mortality was observed in the untreated control (Table 3). No Sevin SL-treated trees died during the experiment. DISCUSSION Carbaryl is considered by many to be the most effective and environmentally safe insecticide used to prevent bark beetle attacks on individual trees (Hastings et al. 2001). In this study, 2.0% a.i. carbaryl (Sevin SL) was effective for pro- tecting P. contorta from D. ponderosae attack for two field seasons, which agrees with results from other authors (Gib- son and Bennett 1985; Page et al. 1985; Shea and McGregor 1987). Furthermore, in both Arizona and California, no mor- tality was observed on Sevin SL-treated trees. The Arizona data are the first report of the effectiveness of carbaryl for preventing I. confusus attack and suggest that 1.0% a.i. may be effective for protecting P. edulis. Carbaryl remains a good choice for control purposes because of its effectiveness, re- sidual activity, low cost, and moderate mammalian toxicity (Hastings et al. 2001). ©2006 International Society of Arboriculture Pyrethroid insecticides offer an excellent alternative to car- baryl. They cause fewer environmental disruptions, have lower mammalian toxicities, and are effective in very small quantities (Haverty et al. 1998). Masterline is a rather novel and unique formulation of permethrin containing methyl cel- lulose (i.e., “plus-C”). The process is thought to increase efficacy and stability by reducing drift, evaporation, and photo, chemical, and biologic degradation of the permethrin molecule. The Masterline emulsifiable formulation contains 38.0% permethrin, which is slightly higher than that of As- tro (36.8%). However, Masterline is registered for use on conifers at rates significantly below that of Astro (i.e., 0.2% versus 0.5%, respectively). The data contained here regarding Masterline is the first published report on its effectiveness for preventing bark beetle attack on individual trees. Our results suggest that one field season of efficacy can be expected even under the most significant of infestations (Table 2), which is similar to that described for other formulations of permethrin (Shea et al. 1984). Based on these results, claims regarding increased efficacy over conventional permethrin formulations such as Astro should be viewed with skepticism until such trials are conducted. We conclude that Masterline is an effective in- dividual tree protection tool, but repeated annual applications will be necessary if multiyear control is desired. Acknowledgments. We thank S.R. McKelvey (Pacific Southwest Research Station, USDA Forest Service, Placerville, CA); G. Kemp- ton and T. Eckberg (Forest Health Protection, USDA Forest Service, Coeur d’Alene, ID); and V. Bunker, T.S. Davis, A. Garcia, C. Hayes, L. Kie, K. Murray, M. Shaffer, and A. Somerville (Univer- sity of Arizona, Cooperative Extension, Flagstaff, AZ) for technical assistance. In addition, we thank D. Conover and J. Eacker (Fruit Grower’s Supply Co., Burney, CA); T. Sexton (Jefferson RD, Bea- verhead/Deerlodge NF); and the Northern Arizona University/ Arizona State Land Department Centennial Forest for providing access to study locations. We also thank T. Worster (Univar USA Inc., Austin, TX) and C. Olsen (Bayer Environmental Science, Wil- domar, CA) for their helpful insights during this study. Univar USA Inc. and Bayer Environmental Science provided the insecticides. This research was supported, in part, by a grant from Univar USA Inc. (Forest Service Collection Agreement No. 04-CO-11272138- 403) to C.J.F. This article was written and prepared by U.S. government em- ployees on official time and it is, therefore, in the public domain and not subject to copyright. LITERATURE CITED Berisford, C.W., U.E. Brady, and I.R. Ragenovich. 1981. Residue studies. In Field and Laboratory Evaluations of Insecticides for Southern Pine Beetle Control. Hastings, F.L., and J.E. Costner, Eds. Gen. Tech. Rep. SE 21. US Department of Agriculture, Forest Service, Southeastern Forest Experiment Station, Asheville, NC.
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