Japanese Beetle Emergence and Management
Below is an e-mail conversation that may be of benefit to other turfgrass managers asking similar questions.
Original message:
From: Golf Courses
Date: Friday, June 22, 9:30 AM
To: Gibb, Timothy "Gibb,
Timothy" <gibb@purdue.edu>
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 ?
Reply:
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
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