Affordable and effective are two terms that come to mind when most turf managers consider using imidacloprid to prevent grub damage to fairways and roughs. However, researchers are reporting that the insecticide’s residual effectiveness is not quite as long as it once was at sites where it was used repeatedly, making application timing even more critical. A standard treatment still provides a high level of control, but the application needs to be made closer to the time when grubs hatch from their eggs. Here are a couple of important questions to consider when controlling grubs:
When is the critical window for control?
In many northern states, Japanese beetle adults are observed feeding on susceptible plants and laying eggs in turf around the Fourth of July. In the past, an imidacloprid treatment made during May would still be effective through July; but as the control interval shrinks, treatments will need to be made closer to the time of adult emergence.
Golf courses have different pest populations to deal with each season, so be sure to identify the grub species that causes the most damage and study its life cycle. In addition, develop a scouting program to document pest problems before applying pesticides.
Why are some courses experiencing “double trouble” with grubs this season?
Long periods of cool weather during spring and summer across the upper Midwest shifted the critical window for grub control into late July and early August. In fact, Japanese beetle adults were still seen during the middle of September on a golf course in the Detroit area. As a result, turf managers that applied imidacloprid during May had two strikes against them: a shorter interval for control and the need to control grubs hatching from eggs during August and September. It should come as no surprise that some courses that treated for grubs in May are experiencing plenty of grub activity this fall.
You can limit these problems by paying careful attention to the interaction between insect pest life cycles and weather patterns. Products that cost a bit more but have a longer residual effectiveness, such as clothianidin and chlorantraniliprole, can be rotated into grub control programs to provide longer-lasting control.
Central Region Agronomists:
Bob Vavrek, regional director – bvavrek@usga.org
John Daniels, agronomist – jdaniels@usga.org
Zach Nicoludis, agronomist – znicoludis@usga.org
Information on the USGA’s Course Consulting Service