Arboriculture & Urban Forestry 32(6): November 2006 287 starch content. Survey data showed that 70% of the respon- dents were willing to tolerate some defoliation (Coffelt and Schultz 1990) with 28% of the citizens considering 25% de- foliation aesthetically acceptable. In addition, analysis of the effect of defoliation on root starch content indicated that 25% defoliation or less would not affect tree vigor (Coffelt and Schultz 1990). Use of 25% defoliation as the threshold pro- vided BPUF employees with guidelines of monitoring oak trees on municipal property and making treatment decisions based on the results of their monitoring. Beginning in 1988, only trees on municipal properties that exceeded 25% damage were treated with pesticides to suppress OSO. Pesticide ap- plication records from 1981 to 2005 were obtained from BPUF, and quantity and selection of pesticides directed to OSO suppression were identified. RESULTS AND DISCUSSION In 1988, the results of implementation of IPM practices were immediate and impressive (Figure 1). Monitoring infested trees and using the 25% AIL resulted in a decrease in pesti- cide use from 39,860 L (10,364 gal) to 7,866 L (2,045 gal), an 80.3% decrease. There was resurgence in OSO popula- tions in 1989 and 1990 that resulted in pesticide applications of 18,000 L (4,680 gal) and 32,399 L (8,424 gal), respec- tively. A steep decline in pesticide use began in 1991. From 1991 to 1998, pesticide applications ranged from 0 (in 1992 and 1994) to 1,573 L (409 gal) (in 1991) with a mean of 250 L (65 gal). From 1999 to 2005, no pesticides were applied for OSO suppression. The sharp decline in pesticide use is attributed to the imple- mentation of several IPM strategies. We feel that the use of the 25% AIL was the key component of the control strategy. It was supplemented by early season monitoring and physical removal of egg masses with pole pruners. The city also changed from synthetic to microbial pesticides. Before 1989, all applications for OSO were full-coverage hydraulic sprays with either organophosphate or carbamate insecticides. Be- ginning in 1989, Bacillus thuringiensis was the primary method of control; it was applied by backpack sprayers to the lower tree limbs where most oviposition occurs (Coffelt and Schultz 1994). By using the AIL as a decision-making tool, Norfolk could apply a uniform intervention standard to the entire city while practicing IPM. Despite the initial success of the program, citizen requests for pesticide application continued for a few years after implementation, no doubt resulting from citizen expectation of “spray on demand” service from prior years. Calls to BPUF and demands for treatment decreased as citi- zens became informed about the IPM strategies in use by BPUF through educational programs delivered by Coopera- tive Extension. Benefits to the city from the implementation of IPM were reducing insecticide costs for OSO suppression to nearly zero (1991 to 1998) and eliminating them entirely (1999 to 2005). As pesticide applications decreased, labor expenses shifted from pesticide application to monitoring of the trees. Even with the additional duties, the total annual cost of OSO management remained below that of the previous 4 years (1984 to 1987) when spraying without monitoring was the standard (Coffelt and Schultz 1990). By 1995, with OSO populations reduced to barely detectable levels, Norfolk eliminated its “spray unit” and reassigned personnel to other roles. With Norfolk’s location bordering portions of the Chesapeake Bay and several of its tributaries, a reduction of the amount of pesticides applied to municipal street trees generates a positive environmental impact. Intangible ben- efits include increased citizen awareness and recognition of the municipality being proactive in environmental stewardship. IMPLICATIONS FOR ARBORICULTURE The long-term benefits of using IPM to lead from the pesti- cide-first strategy to monitoring and scouting with manage- ment decisions based on aesthetic injury levels were demon- strated. Scouting when oviposition is expected, mechanically removing egg masses, using a 25% aesthetic injury threshold, and selecting Bacillus thuringiensis as the control agent were the elements in the successful control strategy. The results show that after IPM implementation, pest populations can remain below aesthetic injury levels for extended periods, currently at 14 years. Acknowledgments. The authors thank Fred Howes, Norfolk Bureau of Parks and Urban Forestry, for his assistance in data collection. LITERATURE CITED Becker, W.B. 1938. Leaf-feeding insects of shade trees. Mas- sachusetts Agricultural Experiment Station Bulletin 353. Figure 1. Pesticide volume for suppression of orange- striped oakworm in Norfolk, Virginia, 1981 to 2005. Coffelt, M.A., and P.B. Schultz. 1990. Development of an aesthetic injury level to decrease pesticide use against orangestriped oakworm (Lepidoptera: Saturniidae) in an urban pest management project. Journal of Economic En- tomology 83:2044–2049. ©2006 International Society of Arboriculture
November 2006
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