392 Frank et al.: Imidacloprid Reduces Defoliation by Japanese Beetles Arboriculture & Urban Forestry 2007. 33(6):392–396. Does Imidacloprid Reduce Defoliation by Japanese Beetles on Linden for More Than One Growing Season? Steven Frank, Robert Ahern, and Michael J. Raupp Abstract. Laboratory feeding trials confirmed that leaves from little-leaf linden treated with imidacloprid were eaten by Japanese beetles far less than those from untreated trees. Field studies revealed that soil applications of imidacloprid significantly reduced the degree of severe defoliation caused by Japanese beetles in the year that the insecticide was applied and also in the next year. These findings indicate that imidacloprid is a useful tool for arborists in reducing defoliation by this important pest. Key Words. Defoliation; feeding deterrence; imidacloprid; IPM; Japanese beetle; linden; plant health care. Lindens, Tilia spp., are one of the most commonly planted street trees in eastern North America, where they enhance the aesthetic quality of life in cities (Raupp et al. 2006). How- ever, lindens are subject to attack by a variety of insect pests, not the least of which is the Japanese beetle, Popillia ja- ponica. Japanese beetles feed on more than 300 species of plants and, among shade trees, lindens are favored hosts (Held 2004). Although resistance has been noted in some species of lindens (Held 2004), insecticides remain a primary tactic for controlling this pest (Potter and Held 2002). Imidacloprid was the first neonicotinoid insecticide to be introduced to the arboricultural market and it is still one of the most popular materials applied in landscapes because of its range of activity against key pests, including leaf beetles (Sclar and Cranshaw 1996; Lawson and Dahlsten 2003), lace bugs (Gill et al. 1999), aphids (Sclar and Cranshaw 1996), scales (Sclar and Cranshaw 1996; Gill and Reeser 1999), psyllids (Young 2002), adelgids (Stewart and Horner 1994; Doccola et al. 2003; Webb et al. 2003), periodical cicadas (Ahern et al. 2005), flatheaded borers (Herms 2003), and leafminers (d’Eustachio and Raupp 2001). However, a recent study by Hubbard and Potter (2006) found that imidacloprid provided poor control of Calico scale, Eulecanium ceraso- rum, on landscape trees. Although systemic products have been used against a variety of insect pests, there are no pub- lished accounts of the efficacy of neonicotinoids for reducing injury caused by feeding of the Japanese beetle. It is the goal of this study to determine the efficacy of imidacloprid in reducing damage caused by Japanese beetles to little-leafed linden, Tilia cordata, as well as whether imi- dacloprid could protect feeding by Japanese beetles beyond the initial year of application. Most studies of imidacloprid ©2007 International Society of Arboriculture efficacy have focused on its toxicity within a time scale of weeks to months after application. Notable exceptions in- clude the work of Sclar and Cranshaw (1996), Webb et al. (2003), and Szczepaniec and Raupp (2007). Sclar and Cranshaw (1996) found imidacloprid to be lethal to European elm scale, Gossyparia spuria, 15 months after soil injections of imidacloprid. Imidacloprid drenches were found to be lethal against elm leaf beetle, Xanthogaleruca luteola, for more than 12 months (Sclar and Cranshaw 1996). Webb et al. (2003) found Eastern Hemlocks, Tsuga canaden- sis, to be free of hemlock woolly adelgid, Adelges tsugae, 816 days after the application of imidacloprid to the soil despite the fact that trees infested with adelgids were nearby in the same landscape planting. Cotoneasters grown in containers demonstrated toxicity to hawthorn lace bugs, Corythuca cy- doniae, for 800 days after the application of imidacloprid to the soil Szczepaniec and Raupp (2007). In addition to elucidating temporal aspects of imidacloprid efficacy, a study was designed to determine if the application of imidacloprid affected the pattern of feeding of Japanese beetles within the canopy of linden trees. Rowe and Potter (1996) and Potter (1998) noted a clear pattern of vertical stratification of damage caused by feeding of Japanese beetles. They found upper-canopy, sun-exposed leaves to be more heavily damaged by Japanese beetles than lower- canopy, shaded ones. MATERIALS AND METHODS Research was conducted at the University of Maryland Turf- grass Research Facility, College Park, Maryland, U.S., during the summers of 2004, 2005, and 2006. Twenty little-leaf lin- den, T. cordata, trees were used. Trees were planted in 2001
November 2007
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