72 First and foremost, public pressure for action may supersede decisions based on the AT. For example, sector 52 was treated for cankerworms although it measured below the AT. This was the result of pressure brought by residents. In this sector, College Avenue is a highly visible public space and damage from can- kerworm larvae was clearly visible. College Avenue is a border street between the city of Regina and Wascana Park, which is managed solely by another agency. This sector was not included in the calculations as a result of the fact that it was considered to be a treated sector. Second, weather influenced control treatment operations, de- creasing the number of sectors that would have been sprayed. Regina experienced higher than normal precipitation, which in turn delayed spraying activities. Had weather conditions been optimal, more sectors could have been completed. For example, sectors 85 and 87 were not sprayed although they were ranked high enough to warrant treatment (Figure 4). Third, this study was limited only to sectors that were not sprayed. We assumed that treatment reduced the amount of de- foliation damage. If true, then the sectors that measured above the AT would have even greater defoliation. However, the con- sequences of proving this point would not likely be acceptable to the general public. Finally, we hope by creating an AT in this manner that we can recognize the potential for a greater than normal pest population and anticipate the potential for damage to the urban forest. By doing so in a rational manner based on a historic perspective, decisions on when control operations are required can be more easily made. That said, there are limits to the city’s ability to respond to cankerworm infestations as a result of the narrow window of treatment effectiveness and the availability of labor, equipment, and weather. Acknowledgments. I thank Wade Morrow and Neil Vandendort for input and permission to use the City of Regina records for this project. I also thank Leroy Bidlo for input toward this paper. Further thanks to City of Regina IPM staff, specifically Geoff McLeod, Brendan Moat, Christopher Dowson, and Wayne Johnson for their work at gathering data relevant to this article. A final thank you to Colyn Lowenburger for review of the statistical analysis in this article. LITERATURE CITED Ball, J., J.E. Lloyd, and D.F. Marion. 1999. The appropriate response process (ARP) and its role in plant health care. Journal of Arboricul- ture 25:24–30. Baum, J.A., T.B. Johnson, and B.C. Carlton. 1999. Bacillus thuringien- sis: Natural and recombinant bioinsecticide products, pp. 189–210. In Hall, F.R., and J.J. Menn (Eds.). Biopesticides: Use and Delivery. Humana Press, Totowa, NJ. Coffelt, M.A., and P.B. Schultz. 1990. Development of an aesthetic injury level to decrease pesticide use against orange striped oakworm (Lepidoptera: Saturniidae) in an urban pest management project. Journal of Economic Entomology 83:2044–2049. ———. 1993. Quantification of an aesthetic injury level and threshold for an urban pest management program against orangestriped oak- worm (Lepidoptera: Saturniidae). Journal of Economic Entomology 86:1512–1515. Johnson, W.T., and H.H. Lyon. 1991. Insects that Feed on Trees and Shrubs, 2nd Ed. Cornell University Press, Hong Kong, pp. 142–143. Kegg, J.D. 1967. Sampling techniques for predicting fall cankerworm defoliation. Journal of Economic Entomology 60:889–890. ©2008 International Society of Arboriculture Eirich: Action Thresholds for Control of Cankerworms Knight, A.R., and D.M. Light. 2005. Developing action thresholds for codling moth (Lepidoptera: Tortricidae) pear ester- and codlemone- baited traps in apple orchards treated with sex pheromone mating disruption. The Canadian Entomologist 137:739–747. La France, K.R., and R. Westwood. 2006. An assessment of tree banding techniques to capture cankerworm defoliators of elm and ash trees in Winnipeg, Manitoba, Canada. Arboriculture and Urban Forestry 32: 10–17. Medenhall, W. 1987. Introduction to Probability and Statistics. 7th Ed. PWS-Kent Publishing Co., Boston, MA. pp. 40, 347–396. Olkowski, W. 1974. A model ecosystem management program. Pro- ceedings Tall Timbers Management Conference on Ecological Ani- mal Control by Habitat Management 5:103–117. Pfadt, R.E. 1985. Insects and humans, pp. 4–5. In Pfadt, R.E. (Ed.). Fundamentals of Applied Entomology. 4th Ed. Macmillan Publishing Co., New York, NY. Philip, H., and E. Mengersen. 1989. Insect Pests of the Prairies. Uni- versity of Alberta, Faculty of Extension. Edmonton AB. 64–65. 71 pp. Raupp, M.J., J.A. Davidson, C.S. Koehler, C.S. Sadof, and K. Rei- chelderfer. 1989. Economic and aesthetic injury levels and thresholds for insect pests of ornamental plants. The Florida Entomologist 72: 403–407. Regina Urban Forest Management Strategy. 2000. Community Services Department, City of Regina, Regina, Saskatchewan. 17, A-3 pp. Weersink, A., W. Deen, and S. Weaver. 1991. Defining and measuring economic threshold levels. The Canadian Journal of Agricultural Economics. 39:619–625. Russell Eirich Entomology Research Analyst City of Regina, Integrated Pest Management Section PO Box 1790 2476 Victoria Avenue Regina, Saskatchewan S4P 3C8, Canada
[email protected] Résumé. Un seuil d’intervention est souvent établi afin de déterminer si des traitements de contrôle des populations de parasites sont requis et quand. En milieu municipal, des traitements de contrôle des insectes défoliateurs de la forêt urbaine sont typiquement établis en fonction des demandes des consommateurs, de demandes d’entretien faites pour des lieux publics hautement visibles, pour des fins économiques ou pour des dommages causés par des insectes. En 2006, la Section de gestion in- tégrée des insectes et maladies de la Ville de Regina a créé une nouvelle méthode pour établir le seuil d’intervention pour le contrôle des vers d’arpenteuse en déterminant si le décompte des femelles d’arpenteuse (Paleacrita vernata Peck and Alsophila pometria L.) était supérieur à 95% du niveau dit normal de population, et ce en se basant sur des données historiques. Zusammenfassung. Ein Schwellenwert ist oft etabliert, um festzule- gen, ob und wann Kontrollbehandlungen beim Auftreten von Krankheiten erforderlich sind. Auf kommunaler Ebene sind Kontrollbe- handlungen für entlaubende Insekten in den urbanen Wäldern typisch- erweise in Resonanz mit der Kundenanforderung, Pflegeanforderungen von öffentlich sichtbaren kommunalen Bereichen, ökonomischen An- forderungen und den aktuellen Insektenschäden zu bestimmen. Die zuständige Stelle für Integrierten Pflanzenschutz in Regina entwickelte eine neue Methode, einen Schwellenwert für die Kontrolle von Spanner- Raupen festzulegen, wenn die Anzahl der weiblichen Spanner-Raupen
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