Purdue Extension Garden TIPS - Insects, Pests, and Diseases Purdue Extension Garden TIPS - Insects, Pests, and Diseases Purdue Extension Garden TIPS - Insects, Pests, and Diseases Purdue Extension Garden TIPS - Insects, Pests, and Diseases
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Purdue Extension Garden TIPS - Insects, Pests, and Diseases

Finding Spring Grubs?

We are getting many calls in the spring from people who find grubs as they are work in gardens and ornamental beds. Don’t panic and run out to buy an insecticide to annihilate these sinister creatures. Even though lawn and garden centers are currently advertising products promising season-long white grub control for home lawns, it makes no sense to apply a white grub insecticide now. These grubs are not feeding actively nor are they in a stage where they are particularly susceptible to pesticides. These grubs will shortly pupate and emerge from the soil as adult masked chafers or Japanese beetles.

The damaging grub stage occurs in late summer after eggs hatch and new grubs feed aggressively on turf roots in late summer and fall. Do not apply an insecticide for white grubs unless you had turfgrass damage last year or the year before. If you have had problems in the past, wait to apply the insecticide until late June or July to control the feeding larvae. This will give you the best value in grub control for your dollar.

Green Flag for Grub Control Applications!!
July 2, 2002

If you have been anticipating the ‘go ahead’ for grub control applications in your lawn, July is the time to 'let ‘er fly.' Keep in mind that this go ahead is only for the application of ‘preventative’ grub control products. These include imidacloprid (Merit) and halofenozide (GrubX or Mach 2). Both products are very long lasting but must be applied as preventative treatments, before the grubs hatch. They may be applied anytime from now until the first week of August for best results. As with all homeowner-applied insecticides, it is critical to follow the label directions exactly when making applications.

On the other hand, recent studies at Cornell University have shown that over 70 percent of all grub control treatments were applied needlessly. Why? Because there were no grubs in the lawn to treat in the first place. I am sure that this is equally true in Indiana. Many homeowners are frightened into applying grub controls because of advertisements on TV, in plant centers, or because of horror stories they have heard about grub damage. The truth is that the ‘just-in-case’ philosophy of applying grub controls is not only expensive but hard to justify from an environmental standpoint unless grubs were present in that area in the past.

We know that grubs tend to return to damage the same turfgrass areas in successive years. So, if you had grubs last year or the year before, chances are that you will have them there again this year. Apply preventative treatments.

A second approach to grub control is a ‘wait-and-see’ or rescue strategy. This involves monitoring for grubs in mid August by using a shovel or trowel to cut a small area of turfgrass (about 6 inches square, down to 3 inches in depth) and searching the soil for white grubs.This should be done in several random locations of the lawn. If no or very few grubs are found, save yourself the expense and trouble of an insecticide application.You will not have grub damage.

If grubs are found in numbers of 5 or more per square foot, (you do the math) a rescue application of insecticide is recommended. Rescue insecticides available to the public for grub control include the active ingredients bendiocarb, diazinon, trichlorfon, isofenphos, or carbaryl (sevin). These can be applied anytime from when you first find grubs (early August) until the first part of September.

For either preventative or rescue grub control products, it is recommended that granular formulations be used and that one-half inch of irrigation be applied immediately after treatment. In cases where irrigation is not possible, timing the application to just before a significant rainfall event is recommended.

General Information

White Grub and Japanese Beetle Pictures

Spring Information

Don't Rush the Grub Control!

Fall Information

Green Flag for Grub Control Applications!! (PDF version)

White Grub Information

Additional Resources

The Virtual Plant & Pest Diagnostic Laboratory (PPDL)

Extension Entomology

Botany and Plant Pathology Extension

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