Grub-Ex-when to treat lawn/garden?

phylrae(z5a/centralNYS)April 22, 2008

I am not sure when to put grub treatment down on the lawn/garden areas(hopefully to eventually cut down numbers of Japanese beetles). I did so last fall in our own gardens, but now wish I had done so with our church garden, where I cannot be, in order to hand-pick JBs! They have made the 12 rose bushes there look horrendous! I don't want to go the trap route, as I know about the traps almost doing the opposite (calling JBs in).

If I put Grub-Ex down now, will it kill existing grubs, and will it have any effect on this summer's population?

Any other suggestions? I am so upset that the one place where I want the roses to look great...looks horrible!


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dan_keil_cr Keil(Illinois z5)

I believe I put mine down in May. They won't hatch until July anyway. So a application in May will wipe out all of the grubs that you are raising in your yard. The only jb's I had were the fly in kind,and there wern't too many. I credit the Merit granules.

    Bookmark   April 22, 2008 at 4:02PM
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madcitymike(z5 Wi)

Adult JBs which were last years eggs will begin to emerge from the ground here in July. They will immediately start to mate and lay more eggs. I believe I read that the eggs take about two weeks to hatch. So the logic follows that if you apply grub killer when you see the first Adult JBs of the season, when their eggs hatch, the merit granules will be there for them to eat, thereby reducing next years population. Any hatchlings that survive will burrow deep into the turf to overwinter, and continue the cycle.
So, I apply it in mid July, and I may put down a second application in Aug. for insurance.


    Bookmark   April 22, 2008 at 5:23PM
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Hey, will grub-ex kill the earthworms?

    Bookmark   April 22, 2008 at 8:18PM
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karl_bapst_rosenut(5a, NW Indiana)

My Master Gardener agent teaches that the best time to treat the lawn for Grubs is in Mid August, when the new crop of eggs have hatched and they are most suseptible to the effects of the grub killer. He says the grubs are too mature in the spring and the grub killer is mostly ineffective if applied then.
My lawn seems to agree with him.
Here's What Ohio State recommends and they seem to agree with Indiana.

"Chemical Controls - Insecticides

The grubs are best controlled when they are small and actively feeding near the soil surface, usually late July to mid-August. However, with the development of new grub control chemistry (e.g., imidacloprid [Merit] and halofenozide [MACH2]), applications in June and July have sufficient residual activity to kill the new grub populations as they come to the soil surface in late July through August. Control of grubs in late-fall or early-spring is difficult, at best, because the grubs are large and may not be feeding. Only trichlorfon (Dylox) and carbaryl (Sevin) formulations are available for such rescue treatments. The key to good control is to make an even application and water thoroughly."
Taken from The Ohio State University Extension Fact Sheet

Here is a link that might be useful: Control of Japanese Beetle Adults and Grubs in Home Lawns

    Bookmark   April 22, 2008 at 10:09PM
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In my experience spring treatment also helps.

    Bookmark   April 22, 2008 at 10:23PM
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When is the best time to apply Grubex?

    Bookmark   June 29, 2011 at 11:55AM
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Don't forget that the July-August grubs are the next generation that would be largest come next spring.

Someone suggested to me some years back that if you apply three times the amount of Grubex per so many square feet in the spring, you will kill the then-big grubs. One competing maker even had in the instructions a 3x application rate for spring versus mid-summer. But this is not practical for most folks.

    Bookmark   September 1, 2013 at 9:42AM
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