The Purdue Plant and Pest Diagnostic Laboratory

What's Hot at the P&PDL
June 25, 2012

Japanese Beetle Emergence and Management

Below is an e-mail conversation that may be of benefit to others asking about Japanese beetles.

Original message:

From: Golf Courses
Date: Friday, June 22, 9:30 AM
To: Gibb, Timothy
Subject: Japanese Beetles Management in 2012

With the early spring we expected to see early Japanese Beetles.  We did not really see any at all this spring or even now.  Do you know why?

Last year our grub treatment was very successful and we had little damage from grubs in the fall. With very dry conditions so far this spring and summer and moderately watered fairways, what do you anticipate grub pressures will be like this fall?

High soil temps and dry conditions during the last two months make me think that we may not have much pressure from grubs. Given that is a significant expense to cover even the watered areas for 36 holes, might this be a year to skip treatment? 

Any thoughts on these?


The Japanese beetles did come out very early this year.  We saw emergence 3 weeks in advance of most years.

A couple of comments to your questions:

(1) The huge numbers and wild fluctuations of Japanese beetle populations that we have experienced in Indiana over the last 20 or so years is starting to moderate. 
This cycle is common with infestations of any new pest.  In early years the populations seemingly run out of control, but over time parasites, diseases and predators naturally catch up and slowly bring the pest numbers down. You will note that Japanese beetles in the Eastern states are not the huge problem that they were when they were first introduced 100 years ago. Their populations have been moderated significantly over the last two decades or so.

After their first introduction it took them many years to slowly make it westward to Indiana.  Once introduced to our state, they quickly became a serious problem every year.

The last 2 or 3 years have been moderated, however and my opinion is that we are now beginning the moderation phase of the pest cycle in Indiana.

Having said that, we still see spotty population outbreaks of Japanese Beetles in IN. For every call like yours asking where the beetles have gone, we get another asking where have all the beetles have come from.  The reality is that they are still a very hit/miss pest.

(2) I would am very hesitant about predicting future grub damage based on observations, or non-observations of adult beetles.  We know that from past MRTF sponsored studies, beetle trap catches do not correlate very closely with the presence of grubs or with turf damage later in the summer. I know that this seems non-logical but the reason in part is due to the ability of the beetles to fly long distances in a short period of time. 

Our research in Indianapolis indicates that a mile is no real challenge for a motivated beetle to fly.  This, coupled with the dry season that we are in right now and the fact that you are irrigating your turf, means that beetles down wind of you may be on the verge of moving into your area to lay their eggs.  Irrigated turfgrass is a magnet for beetles in a dry year such as this one.

We have always suggested that if you are going to skip a grub application with confidence, you have to sample. Sampling is work - but it can also save you pesticide application costs.  It may very well be that you will not
have grubs this year, but I would not count on it just because of a light beetle flight.  Sampling fairways in August is what I would base my decision on if I were you.

Hope this helps

Tim Gibb


Click image to enlarge

Japanese beetle on leaf

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service