Daniel A. Herms, Department of Entomology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, Ohio.
The phenological sequence from 1997 to 2002 is presented in Table 1. Substantial variation in weather resulted in differences of up to four weeks in the dates on which these events occurred from year to year (see Table 1 for the earliest and the latest date of occurrence for each event). Most events occurred earliest in 1998, the year of El Niño, which was characterized by an early warm spring, and latest in 1997, the spring of which was quite cool.
Species that were not monitored in 1997 exhibit a more narrow range of dates in their phenology. However, dates are presented only to provide a frame of reference. Rather, it is the sequence of phenological events that is the most valuable for pest management purposes.
Despite substantial variation in degree-day accumulation, the order in which phenological events occurred was quite consistent between 1997 and 2002 (see Herms, 2002). Even the mild winter of 2001-2002 had little effect on phenological patterns. Figure 1 illustrates the high degree of correspondence between the sequence of events in 2002 and the average sequence from 1997 to 2001. Indeed, aside from first bloom of silver maple, no phenological event had its earliest date of occurrence in 2002, and cool weather in March actually delayed phenological development during early spring relative to the six-year average. Most events, however, occurred within just a few days of the six-year average (Table 1).
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Figure 1. Comparison of the sequence of insect and plant phenological events in 2002 with their average order of occurrence from 1997 to 2001 in Secrest Arboretum, Wooster, Ohio. Rankings are based on cumulative degree-days for each event, which were calculated using a base temperature of 50F and a starting date of January 1. The line that bisects the graph represents exact correspondence, with the distance of a point from this line indicating degree of variation between 2002 and the average of the previous five years (r = 1.0 would indicate perfect correspondence). |
The mild winter had little effect on plant and insect phenology because temperatures rarely exceeded 50F for very long, which for most plant and insect species approximates the lower temperature threshold for development (which is why 50F is often used as the base temperature for calculating degree-days). Once the temperature drops below the lower threshold, physiological development ceases no matter how cold or mild the weather is.
Because phenological events occur in the same order each year, the phenological sequence can be used a Biological Calendar for predicting pest emergence and scheduling pest-management activities, such as monitoring programs and pesticide applications. This can greatly simplify the complex logistics associated with developing a monitoring and control schedule for the great diversity of insect pests in nurseries and landscapes.
For example, instead of monitoring every plant and pest species in the nursery on a weekly schedule, the Biological Calendar can be used to schedule monitoring programs only for those pests that are due to appear soon. For example, when common lilac is blooming, gypsy moth eggs have already hatched, but it is still too early to monitor for bronze birch borer emergence. Conversely, once black locust has bloomed, it is too late to control the first generation of pine needle scale.
The great consistency in the phenological sequence demonstrates that even one year of observations is useful for timing pest management decisions. This means that users can readily create, expand, and customize the Biological Calendar to suit their own purposes.
For example, a user could note what plants happened to be in bloom when a pesticide application was made (even if those plants are not included in Table 1). If follow-up monitoring showed the application to be effective, then the timing of the spray could be duplicated accurately the following season.
If the application was found to be too early or too late, then timing in future years could be delayed or accelerated relative to the phenological sequence. Any additional plants or pests can be added to the calendar by noting when they are active relative to events already included.
A phenology web site — http://www.oardc.ohio-state.edu/gdd — has been developed by Dave Lohnes (OARDC, Section of Communications and Technology) where cumulative degree-day data is accessible to users in real-time for any location in Ohio and is linked directly to the Biological Calendar.
Daily temperature data from the 12 OARDC Research Stations around Ohio are used to calculate cumulative degree-days in real-time for any location in the state. Degree-days for locations between weather stations are extrapolated from climatic isotherms for Ohio.
Upon entering any Ohio zip code, current degree-day accumulation for that location is calculated, and the grower is directed to the appropriate spot on the BioCalendar. Users can scroll up or down to see what pest events have already occurred, as well as what has yet to occur. The web site is still being updated with links to photos, fact sheets, as well as pests of other agricultural commodities.
In summary, this research demonstrates that this Biological Calendar can be used accurately to track degree-day accumulation and predict pest activity, because the phenological sequence of insect emergence and plant flowering remains remarkably consistent from year to year, even when weather varies considerably. Using the Biological Calendar and phenology web site to predict pest emergence and time management activities can increase the effectiveness and efficiency of pest-management programs in landscapes and nurseries, while decreasing pesticide use.