Japanese Beetles – Gardeners, Unite to Fight the Beetle!

By Carol Van Why

Before moving to Coffman Richard Zeyen and I gardened in St. Anthony Park for 31 years.  We accommodated the filtered sunlight and dense shade that the Park is famous for by NOT growing vegetables, instead planting a variety of shade tolerant perennials.  Daylilies, astilbes, wild ginger and of course hostas were staples in our gardens.

I guess since we were not growing edibles we were quite blasé about insects in our garden, beneficial or otherwise.  Of course we put up with mosquitoes and gnats and slugs on our hostas just to be outdoors enjoying those fleeting summer months.  When we obtained a Coffman garden plot we couldn’t wait to plant tomatoes, basil, a couple of peppers and a few flowers.  But after just two months of Coffman “farming” I was astonished at the extent of infestation and damage caused by Japanese beetles in our garden plots.

Because I was not expecting them I don’t remember when I first became aware of the beetles last summer.  I know they appeared initially on the basil and zinnias and then they began feasting on the morning glory leaves.  Little did I know at the time but these plants are some of the pest’s favorites!  Eventually I found them feasting on Reece’s beans and nearby raspberry bushes.  There were hundreds of them just in our small corner of the plot area.  Curiously, some areas of the garden were crawling with beetles and others were relatively untouched, but I’ll save that for a later discussion.

By then, I’d started reading about the Japanese beetle.  I chuckled at extension service pamphlets that advised one to pick them off the leaves and pop them into a small jar!  I could envision squads of Coffman residents signing up for this daily duty!

About that time I hustled off to Linder’s to search for a non-pesticide solution to the problem.  Those of you who gardened last year might remember seeing the first beetle trap that Richard Zeyen and I placed near the western edge of the plot area.  The trap was essentially a plastic bag that contained an irresistible pheromone that drew the Japanese beetle into a narrow entryway.  They were powerless in the face of its attraction and once they checked in they couldn’t check out!  By the end of just a week we’d trapped at least 500 beetles.

It doesn’t take a statistician to figure out the reproductive capacity of an organism when you’re dealing with numbers of this magnitude.  So, I went back to the literature and it was discouraging.  One of the best sources of information I ran across was the USDA’s  Managing the Japanese Beetle: A Homeowner’s Handbook.  According to the experts the Japanese beetle is not native to this country, having arrived in the eastern U.S. in 1916 and gradually moved deep into the Midwest.  It is very destructive causing extensive damage to agricultural crops as well as to turf grass in lawns, parks and golf courses.  It has no natural enemies and in the Coffman property it has found an environment with everything it needs to thrive.

In early summer when the beetles began to appear in the garden we were seeing the adult form of the species.  The only job the beetle has at this stage is to eat and breed.  Females take time out from eating to burrow into the ground, and deposit eggs, eventually laying 40-60 eggs per female.  The eggs hatch below ground in mid-summer and the grub form appears and begins feeding on roots.  Lawns that exhibit patches of brown or dead looking grass in mid to late August likely host Japanese beetle grubs.

As fall approaches the grubs burrow deeper into the soil and overwinter in an inactive state.  In early spring they move up to the root layer again and begin feeding.  At some point they turn into a pupae stage until early summer when they emerge from the ground as the classic, winged adult beetle and the cycle begins anew.

In the U.S. various pesticides have been used to control the Japanese beetle.  However, since it’s Coffman’s goal to eliminate or at least minimize their use on our grounds we must consider other methods to control this pest.

In addition to grazing on our lawns Japanese beetles are known to feed on over 300 species of plants.  At Coffman we have provided them with four of their favorite woody plants – crab apples, lindens, black walnuts and willows.  What’s more, in our gardens we’ve planted herbaceous favorites such as basil, beans, dahlias, evening primrose, hollyhocks, morning glories, peppers, raspberries, rhubarb and zinnias.  We’re not about to get rid of any of the trees so if we want to reduce the infestation over time there are steps that we can take.

Fortunately there are plants that the Japanese beetle does not find tasty at all – ageratum, columbine, dusty miller, begonia, coreopsis, coral-bells, hostas, impatiens, pansies and nasturtiums to name a few.  It’s possible that having some of these in the garden last year explains why some plots were overrun with beetles and others, despite containing susceptible species, did not see as many beetles.

Since the zinnia is my favorite annual I’m the last person who would want to ban them from our garden plots.  But this year if I want to plant a few zinnias I may also decide to plant some nasturtiums.  It might also make some sense to plant a defensive border of dusty millers near our community rhubarb plants!  Probably the best news is that thanks to the work of several Coffman residents, steps have been taken to reduce turf grass on the property by preparing and seeding our new meadow.

Along with conscious decisions about what to plant where, there is a strong argument for systematically placing beetle traps on our property in 2010.  Clearly, the grub form of the Japanese beetle is feeding on the tender roots of Coffman’s lawn as you are reading this. With the numbers of adults we saw last year we know we’ll have our own homegrown infestation appearing before long.   We need to systematically place traps at the periphery of the gardens as soon as we see the first adult beetle.  Only by trapping fertile adults and reducing their feeding and breeding can we hope to make a dent in the infestation this year and into the future.


An additional note by Marcie O’Connor

Click HERE to see an article about Japanese Beetles put out by the U.  Note that they suggest using insecticides to control them, and that most of the pesticides are dangerous for bees, birds and other wildlife.  I would vote strongly against using any pesticides.  Even if we reduced the numbers of beetles in our immediate area – at great cost to other wildlife – they would be back as soon as we stopped using the pesticides.

Also – the pheromones attract beetles from surrounding areas, and the traps only capture some of them.  So we may be attracting more beetles to our gardens than we would have without the traps.  The golf course – with its extensive lawn area – is a perfect place for the beetle larvae to thrive.  We may be encouraging golf course beetles to come and try out our gardens.

I think in the long run, we will have to learn to live with these beetles.  I think the methods used to control them are worse than just living with them.