You Are Here: Management Updates 2002 Archive August 15, 2002

Date: August 15, 2002
Category: Insects
Subject: Is it Too Late to Use Merit to Control Grubs This Year?

We have been receiving numerous telephone and e-mail inquiries about whether it is too late to use Merit to control grubs this year. The short answer is that it is a very complicated question! While in most years it would be too late to use Merit, the current weather pattern has impacted beetle behavior. Meanwhile with the complex of grub species active in New England, the answer relative to Merit will depend on local conditions.

What species of grub do you have?

Remember that many turf managers in New England are dealing with European chafers, and their life cycle is usually about two weeks EARLIER than that of the Japanese beetle. Usually we recommend that any Merit applications made against European chafer populations should be in place by the end of July. (Also keep in mind that European chafers prefer dry soils, so we can expect those grubs to thrive this fall in many locations.) Indeed, the grubs are already active in some spots.

Also field trials from throughout the country have documented that Merit is markedly less effective against European chafers and oriental beetles than it is against Japanese beetles. So it is really important to use the product as efficiently as possible when targeting these species. In most cases I believe it is too late to use Merit against European chafers and in many cases, it is probably too late to use it on oriental beetle populations.

What about the Japanese beetle?

It appears that many Japanese beetle females have been holding on to their eggs, waiting to lay them once soil moisture improves. The drought conditions affecting so much of New England have forced this "delay", but once the autumn rains return, the females will be anxious to lay their eggs as quickly as possible. Some of the earliest beetles to emerge may have lain some eggs in July, but if those areas were subsequently hit with extended periods of no rain and were not irrigated, many of those grubs would have succumbed to the dry conditions.

In any case, because many of the beetles have not yet laid their full complement of eggs, Merit applications against Japanese beetles may still be quite effective this year, but in general you should aim to complete those applications by 25 August.

There is a MAJOR caveat, relating to turf vigor and dormancy:
What happens if we apply Merit when the turf is in summer dormancy?

Merit has some systemic qualities, and so is normally taken up into the roots of the turfgrass plant. However, if the plants are in dormancy, that uptake is greatly reduced. So applications under current conditions (at least in unirrigated turf areas) may not be as effective as expected.

Finally, keep in mind that any grub application, regardless of active ingredient and regardless of formulation, MUST BE WATERED IN. That may be the biggest challenge of all in some areas. With soils already being very dry, it is even more important to water in the application, but of course some municipalities will not permit it.

(A note for next year - at least some towns in Pennsylvania instituted watering bans but recognized that a one-time exemption would be appropriate to allow homeowners to water in a grub insecticide. Perhaps we in New England need to learn from their foresight, and should lobby for similar wording in watering bans here.)

- Submitted by: Dr. Pat Vittum