A phenological sequence of the blooming periods of ornamental plants can provide a user-friendly approach to predicting insect activity. Phenology is the study of recurring biological phenomena and their relationship to weather. Because the development of both plants and insects is temperature dependent, plants can accurately track the environmental factors that affect insect development. Plant phenology is easier for nursery managers to monitor than are difficult to detect insects, and can be used to predict the order and time pests reach vulnerable stages. This would greatly simplify the logistics of managing a great diversity of pests.
A five-year study conducted by Herms in Michigan demonstrated that a plant phenological sequence can be used effectively as a biological calendar to accurately predict insect activity, and that even one year of phenological data can be very useful because within a region there is little year-to-year variation in patterns of plant and insect phenology, even when there is substantial variation in degree-day accumulation. However, evaluation of the Michigan sequence in Ohio shows that phenological indicators developed in one geographic region are not always accurate when applied in another region, making it necessary to develop a phenological sequence for Ohio.
The objectives of this project were to (1) identify a phenological sequence of flowering ornamental plants that can be used as a "biological calendar" for timing the seasonal appearance of key insect and mite pests in Ohio nurseries, (2) to quantify degree-day accumulation for each insect and plant phenological event, and (3) provide scouting and monitoring data and training to growers.
The phenology of 86 plant species and/or cultivars and 40 species of arthropod pests were monitored. Plants were chosen to represent a range of blooming times from early March through late July. This time period corresponds with the activity of most of the important insect pests of ornamental plants. Four individuals of each species or cultivar were monitored at least three times each week, and the dates of "first bloom" and "full bloom" recorded, with "first bloom" defined as the date on which the first flower bud on the plant opens revealing pistils and/or stamens, and "full bloom" as the date on which 95% of the flower buds have opened. These phenological events can be identified and recorded with precision by multiple observers.
The 40 insect and mite species monitored represent diverse feeding guilds including defoliators, scales and other sucking insects, gall formers, wood borers, leafminers, and root feeders. As opposed to methods used to monitor plant phenology, which were designed to minimize variation in order to increase predictive power, sampling protocols for insects were designed to characterize the phenology of the entire population. Key phenological events such as egg hatch and adult emergence were monitored using techniques appropriate for each species, including pheromone traps, visual monitoring, sticky cards, light traps, and beating methods. Cumulative degree-days were calculated from daily maximum and minimum temperatures for each phenological event using the double sine wave method from daily maximum and minimum temperature data using a base temperature of 50º F and a starting date of 1 January.
The easily monitored blooming sequence used as a "biological calendar" to predict the order and time pests reach vulnerable stages should facilitate implementation of IPM by increasing the efficiency of monitoring programs and improving timing of pesticide applications. The net effect will be to decrease the number of pesticide applications, and increase acceptance of short-residual biorational products. For example, we found that when common lilac was in full bloom (1) crawler emergence of pine needle scale was well underway and that sprays were appropriate at that time, (2) pheromone traps for lilac borer should have been deployed promptly, and (3) there was still time to plan for bronze birch borer. A useful attribute of the phenological sequence is that they can be readily expanded and customized. Once the basic sequence is in place, any new plants or pests can be added as the need occurs. For example, if a pest manager has made a particularly successful treatment, any plants in bloom at the time can be noted, added to the sequence, and used to duplicate the timing in future years.
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