Cedar Valley Arboretum & Botanic Gardens

Beetles are BACK!

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Japanese Beetles are back and as ferocious as ever!  Below is a quick refresher course on Japanese Beetles – the full article was found in The View last September.  If you would like to receive The View, The Arboretum’s e-newsletter, please email office@cedarvalleyarboretum.org.

IMG_5822 If you didn’t find this ferocious eater in your garden this year, consider yourself lucky.   Japanese beetles, Popillia japonica Newman, are less than ½inch long with green bodies and metallic-gold outer wings.  The beetles eat the leaf tissue found between the veins and can quickly skeletonize whole trees. 

USDA maps report Japanese beetles steadily moving west from the east coast, though not yet well established west of the Mississippi River.   I have spoken with Extension specialists that believe populations will fluctuate from year to year, and next year we might not see the same damage.  But I think it’s safe to say Japanese beetles have found their way into the Cedar Valley.  However, adopting a more holistic approach of pest management will provide more successful future control.

For this season, the damage has been done.   If there is an upside, Japanese beetles defoliate late enough in the summer that trees will not try to put out new leaves before winter, thus further depleting their energy reserves. While not the case for all species and situations, the rule of thumb is that trees can handle three years of consecutive defoliation. So if you began the season with healthy and vigorous trees, there is no reason for alarm. At The Arboretum, we will monitor damaged trees over the following months, but expect trees to leaf out as normal next spring.

So what can we do?  The most effective management strategies include chemical, mechanical and cultural controls.

I come from a farming family and can appreciate there is a time and place for chemicals, but I would prefer to use them as little as possible.  There are several pesticides on the market to control adult populations, but there has been little success for residual control, resulting in costly and environmentally unsound routine applications.  Better control is attacking the Japanese beetles before their damaging stage.  We have seen the most damage late July into August.  Before this, Japanese beetles remain just below the soil surface as grubs.  A series of ground applications in early summer is safer than overhead application, and has more of an impact on the younger, more vulnerable, life stage of the beetles.

A popular mechanical control is traps that releases pheromones to attract the beetles, and can be an effective and inexpensive if used properly.   It is important to remember that traps attract Japanese beetles, so they must be placed away from gardens and other susceptible plant material.  While more time consuming, consistent hand-picking is perhaps the most effective control method.  In isolated areas like The Arboretum’s  Rose Garden, we continue to keep damage to a minimum by hand-picking on a regular basis.

Cultural control methods include maintaining a healthy tree and plant population.  Like all disease and pests, unhealthy and damaged trees are more susceptible to Japanese beetles. The smell of diseased or fallen fruity is also an attractant. And although Japanese beetles feed on hundreds of plants, there are species that are more susceptible.  That does not mean we will cut down all Lindens and Horse Chestnuts at The Arboretum, but having a well-rounded collection of preferred with non-preferred species can reduce beetle-caused damage.

Species resistant to adult Japanese beetle feeding:  Magnolia, Redbud, Dogwood, Red maple, Northern red oak, Burning bush, Boxwood, Ash

 Species susceptible to adult Japanese beetle feeding:  American Linden, Crabapple, Japanese maple, Pin oak, Norway maple, Rose, Birch

 Another method that might be an option for your garden is biological control. While results are not as quickly apparent as with the use of pesticides and traps, biological controls last longer in the environment and do not harm non-target organisms. Most biological controls –such as nematodes, milky spore and parasites – are applied to the soil and attack Japanese beetles in their grub stage.

Have other methods you’ve tried in your garden?  Please share!  Communication can be the most valuable tool, and localized efforts are always the best defense.  Please send me an email at director@cedarvalleyarboretum.org.

See you in the gardens.


Written by cedarvalleyarboretum

July 31, 2009 at 8:49 pm

Posted in Uncategorized

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