Using nature’s clues to manage landscape pests

This year more than most, use of local growing degree day accumulations can help pinpoint management stages in the life cycle of insects.

For most of us in Michigan, spring does not come quick enough. We are teased by temperatures in early spring that rise into the 60s just to plummet back into the teens at night. Slowly, winter’s icy grip is replaced by cool spring days. In nature, these changes in temperature bring plants out of their slumber or winter dormancy, and as the plants become active so do the insects that feed on them. This connection between temperature and insect activity provides insight into when these insect life stages will occur.

Today, scientists predict insect activity by a system, called Growing Degree Days (GDD), which measures the daily accumulation of temperatures averaging above 50 degrees. This system can be used as a tool to determine the hatch of pine needle scale, emergence of beetles such as emerald ash borers, or even to time when black vine weevils will be feeding on rhododendron leaves. Variations in temperatures across the state cause differences in when insect activity will occur. For the GDD system to be meaningful to landscape and nursery professionals, it requires the availability of local degree day information. As more weather station sites have been developed across Michigan, it has improved the accuracy for timing insect activity. Michigan State University’s Enviro-weather web site provides current GDD information for monitoring and managing specific pests of landscape and nursery pests. Learn more from Enviro-weather coordinator Beth Bishop’s article on Looking at growing degree days: Just how far behind normal are we?

Whether you are managing pine shoot borer on a Christmas tree farm, gall forming insects on spruce in a nursery, or Magnolia scale in the home landscape, use of local GDD information through Enviro-weather can help pinpoint critical management stages in the life cycle of insects. This type of accuracy reduces the need for multiple pesticide sprays. A check of the closest weather station to you at the Enviro-weather site gives current degree days for your area, helping to time management options.

This year more than most, it is critical to monitor degree days instead of using treatments by a certain date, since current degree day data shows temperatures are running one to two weeks behind for much of Michigan. Basing any pesticide treatments on a calendar date would be poorly timed and could prove costly as spring temperatures fall short of the average for Michigan.

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