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Daniel A. Herms, Ohio State University/ Ohio Agricultural Research and Development Center/Entomology |
Planning and implementing a successful pest-management program for landscapes constitutes a logistical challenge because of the tremendous diversity of ornamental plants, each with its own complement of insect pests. Insecticide applications must be timed precisely to maximize their effectiveness and minimize the number required. This is especially true of the environmentally friendly but short-lived "biorational" insecticides such as horticultural oils and soaps, and for insects such as scales and borers that are only susceptible during specific stages. Many insects are difficult to detect and monitor, further complicating the accurate timing of pesticide applications. Consequently, pesticide applications are frequently scheduled on a calendar-day basis. However, because of variation in patterns of degree-day accumulation from place-to-place and year-to-year, calendar-based scheduling is frequently inaccurate.
The use of plant phenology provides an alternative approach for predicting insect activity. Phenology is the study of recurring biological phenomena and their relationship to weather. Bird migration, hunting and gathering seasons, blooming of wildflowers and trees, and the seasonal appearance of insects are examples of phenological events that have been recorded for centuries (Glendenning, 1943; Levitt, 1981).
Because the development of both plants (Rathcke and Lacey, 1985) and insects (Tauber and Tauber, 1981) is temperature dependent, plants accurately track degree-day accumulation and insect development. Indeed, the use of plant phenology to predict insect activity is an old practice, with recorded observations dating back at least to the 18th century (Huberman, 1941). Recent studies have shown that the phenology of many birds, plants, and insects has been altered over the last 50 years in response to global warming (Bradley, et al. 1999; Menzel and Fabian, 1999; Peñueles and Filella, 2001).
The critical assumption in the use of plant phenology to predict pest activity is that the phenological sequence (the order in which phenological events occur) remains constant from year-to-year even when weather patterns differ greatly. A comparison of phenological patterns in the Secrest Arboretum at the Ohio Agricultural Research and Development Center in Wooster from 1997-2001 provides an ideal opportunity for testing this assumption. Weather patterns varied substantially over this period. Spring 1997 was delayed and cool, while 1998, the year of El Niño, was characterized by an early warm spring, and the springs of 1999, 2000, and 2001 were intermediate.