Annual bluegrass weevil biology and weather factors

One of the reasons that annual bluegrass weevil (ABW) is so difficult to manage is the variability associated with the timing, intensity and duration of its attack on annual bluegrass.

This variation is a function of the widely different environmental conditions that occur during the spring. And no two springs are exactly alike, so ABW behavior one year may differ greatly from the next.

In ideal circumstances, winter transitions to summer with gradually warming spring weather and intermittent rain events. This causes overwintered adult ABW to move from overwintering sites during a relatively short period of time, and results in a narrow period of intense egg laying activity.

When this occurs, one or two insecticide applications can successfully maintain ABW populations below damaging levels for most or all of the summer.

It is rare that spring provides a gradual transition from winter to summer. April and May are usually marked by alternate periods of unseasonably warm and cool weather, and some years experience prolonged periods of rainy weather. These varying conditions greatly impact the behavior of overwintered adult ABW and result in wide extremes in the intensity and duration of egg laying and subsequent larval development.

So instead of a narrow peak of egg laying, there may be a prolonged period when eggs are deposited and larvae subsequently damage turf.

This prolonged egg laying period makes ABW management most difficult because adult activity may be rather cryptic, and the need for multiple insecticide applications often goes unnoticed until the annual bluegrass begins to quickly fade during the first hot or dry spell in June.

ABW management is further complicated by the fact that differing microclimates on an individual course can result in up to a 10-day difference in ABW development.

For example, an open fairway with a southern exposure will experience earlier egg hatch than a nearby fairway that has a northern exposure and is lined with evergreen trees. It is unusual that a single insecticide application could be made at the proper timing for both of these locations.

Successful spring management of ABW does not always mean that turf will be free of damage through the summer months. Even the most successful spring control programs don’t totally eliminate the ABW population, and in years when high populations are present, sufficient numbers of ABW survive into the summer months, causing damage from second or third generation larvae.

This is especially true considering that summer weather conditions place annual bluegrass under tremendous stress so that a minimal amount of ABW feeding (that wouldn’t even be noticed when the plants are vigorously growing in the spring) causes unacceptable damage in the heat of July and August.