The flower signal

Phenology is the science of monitoring nature’s signals that let you know how weather and climate are progressing. By studying recurring biological phenomena (like plants blooming, insect eggs hatching and bird migration) and their relationship to the weather, you can predict pest activity. If you know when the pests are coming, you can plan for their arrival and treat them with the proper product.

“Accurate timing is important to being effective and reducing the number of applications that are needed, both of which save money and improve the quality of the pest management program,” says Dan Herms, chair of the Department of Entomology at Ohio State University.

Because pests and plants respond to temperature in the same way, the plants can be used as a biological calendar. And by using that calendar to schedule your spraying, you can increase the pesticide effectiveness. According to Herms’ research, degree-day models can be used quite accurately to predict the appearance of insect pests. These models use a measurement called growing degree days. Degree days are a way of measuring how much heat has accumulated over the course of a season and how fast the growing season is progressing.

The base temperatures used in degree days are based upon the temperatures above which certain plant or insect growth occurs. Different plants have a different base temperature above which they will start to grow, and their growth will typically be roughly proportional to the amount by which that base temperature is exceeded.

Weather varies from year to year, but these events always happen in the same order. That is the key to accurate timing of pesticide application and other pest management tactics.

“Those events occur in the same order every year, we’ve found through our research,” Herms said. “Whether it’s a warm spring or cool spring, they still occur in the same order, though not necessarily on the same calendar day.”

Growers can follow the blooming sequence in their nurseries and use that to predict when pests will be active. When the lilacs are blooming, growers know that it’s time to monitor for pine needle scale egg hatch. If black locust is blooming, look for black vine weevil.

For this system to work, you have to know how many cumulative growing degree days or heat units are required for a particular pest to emerge or hatch. He recommends checking with your local state extension service and the USA National Phenology Network (www.usanpn.org). The USA-NPN monitors the influence of climate on the phenology of plants, animals and landscapes. The network collects, shares and uses phenology data, models and related information. Citizen scientists, naturalists, non-profit groups, and government organizations all collect and report data either independently or through the USA-NPN’s online database and visualization tool. The network has developed a standardized approach to phenology, so its community of researchers are all using the same system.

Although phenology can be a helpful part of an overall strategy, Herms said the true key to a successful pest management program is monitoring.