The Purdue Plant and Pest Diagnostic Laboratory

What's Hot on May 25, 2006
at the P&PDL!

Understand life cycles is key to controlling grubs

Tim Gibb, Insect Diagnostician, Department of Entomology, Purdue University

Each spring we receive many calls about grubs as people find them while planting gardens or ornamental beds.  These are often large and appear menacing however do not let their appearance cause you to worry, panic or run out to buy an insecticide to annihilate these sinister creatures. These grubs are not feeding actively so will not cause serious damage and are not in the stage where they are susceptible to pesticides.

It’s important to understand the lifecycle of white grubs before considering control. The large larvae that occur in the springtime are preparing to enter into a pupation stage, preparatory to emerging as adult masked chafer and Japanese beetles.   When they emerge (in June and July) the adults will mate and lay eggs. Eggs hatch from mid-July to early August. Newly hatched grubs are the more serious threat because they feed very actively on roots sometimes causing damage to turfgrass as they grow.

During the fall, when the temperatures cool, the large larvae quit feeding and move down deeper into the soil to pass the winter. As the weather warms again the following spring, the larvae generally move back up to within 1 or 2 inches of the surface where the cycle repeats itself.
It is rare that grubs cause significant damage in gardens or flower beds.  Do not be tempted to over react to their presence there.  In turfgrass, especially where grabs have caused damage in the past, wait to apply an insecticide until late July or early August to control the feeding larvae. This will give you the best value in grub control for your dollar.


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grubs

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