Horticulture Forum: April 1998, Phenology

One of the great frustrations for landscape maintenance professionals is trying to predict when insect pests are in their early, and most treatable, stages of development. In general, it takes judicious scouting and climatic observation to determine when is the best time to apply control products.

But what if you could predict the development of tree and ornamental insects by simply observing the emergence or blooming of a specific plant species? Rather than having to get out in the field and search for the critters, you could drive by Mrs. Jones’ house and see if the forsythia were blooming.

Too good to be true? Not according to Daniel Potter, professor of entomology, University of Kentucky, Lexington. With graduate student Guy Mussey, Potter spearheaded a three-year project comparing the activity of insects and how they coincided with the development of trees in the spring and summer.

A DEFINITION. Phenology is defined as the science dealing with the effects of climate on seasonal biological events, which include pest emergence and plant flowering. Plants and pests share a common bond in that their emergence is dependent on the changes brought about when the weather warms in the spring.

Theoretically, by observing pest and plant activity simultaneously and keeping detailed records, one could eventually draw conclusions about insects by observing the plants.

ALL IN THE TIMING. Potter’s research is ground-breaking, but the concept is nothing new.

In 1989, scientist Don Orton published the book Coincide, which contained a lifetime of observations about plant and insect emergence and how the two are interrelated.

About the same time, Dan Herms, presently an assistant professor at The Ohio State University/Ohio Agricultural Research and Development Center, Wooster, began comparing data he had been maintaining on the phenology of blooming trees to the emergence of pests while employed at Dow Gardens in Midland, Mich. His methodology was the foundation for Mussey’s and Potter’s research.

They targeted 33 of the most common turf and ornamental insects, and tracked their spring emergence each year for a three-year period.

At the same time, observations were made about the emergence of flowers in 34 common landscape plants in Kentucky. Three specific events were noted: first bloom, when the plant produces its first flower; 50 percent bloom, when half of the blooms on a tree have flowered, and 95 percent bloom, when the plant has essentially reached full flowering.

Mussey and Potter’s findings have spurred similar studies in Georgia, Pennsylvania and Ohio, where Herms is reconstructing the experiment at the OSU/OARDC. His concern in performing the research is answering the question, can the findings from one state be duplicated in another? After one year, the answer is both yes and no.

"For about 2/3 of the insects, we’ve found that the predictions Mussey and Potter made are pretty darned accurate," Herms stated. "Where we’ve found significant discrepancies has been the soil-borne insects."

Herms will be replicating the experiment in future seasons to see if he can achieve a higher level of predictability.