Attack of the Japanese Beetles!

Mature Japanese Beetle

They're Back!

Well, whether you are ready or not the swarms of Japanese Beetles are back. They are back a little early this year due to the hot dry weather we have experienced so far this year. So, where do they come from in the first place (Japan duh!)? The beetles lay eggs in the soil and grubs burrow and live about 2'' to 8'' down in the soil. When the soil cools to about 60°F in the fall, the grubs begin to move deeper. Japanese beetles overwinter in the grub stage and most survive the winter 2 to 6 inches below the surface, although some may go deeper. They become inactive when soil temperature falls to about 50°F. When soil temperature climbs above 50°F in the spring, the grubs begin to move up into the root zone, feeding on the roots of grass, sometimes causing dead patches in yards. Following a feeding period of 4-6 weeks underground, the grubs pupate and remain there until emerging as adults and feed for 30-45 days. In total, these insects spend about 10 months underground and then emerge typically in mid-summer. When they emerge they do two things very well: feed on your plants and make more baby beetles.

So, naturally you may ask: what plants do they feed on? Well, the list is too long for this post. Japanese beetles feed on about 300 species of plants! But, we can talk about some of their favorites that may be in your yard. Some of their preferred hosts include the following:

-Japanese Maple

-Norway Maple

-American Elm

-English Elm

-American Linden


-Cherry, Peach, Apple, and Plum trees

-Black Walnut


-Flower Crabapple


-River Birch

-London Planetree

Some tree species that are not preferred hosts, but may incur light feeding include:

-Red Maple

-Silver Maple


-Shagbark Hickory

-White Oak

-Scarlet Oak

-Red Oak

-Black Oak

-Tulip Tree

-White Ask

-Green Ash

-Flowering Dogwood

-American Sweetgum

What Can We Do About Them?

Typically once you begin to notice damage in your landscape the invasion has already begun. There are treatments that can be done in the spring in anticipation of a Japanese Beetle infestation to avoid damage to trees and shrubs. Typically this involves the application of a systemic insecticide that resides in leaf tissues and makes the leaves unpalatable, and will kill the beetle if ingested. However, if you are like a lot of people, and are just now assessing the damage and looking for help there is still hope. There are a number of chemical controls available that can kill adult Japanese Beetles. Chemicals containing pyrethroids and carbaryls are excellent at controlling the beetles. In generally, pyrethroids provide 2-3 weeks protection of plant foliage while carbaryls afford 1-2 weeks protection. Examples of pyrethroid and carbaryl products are as follow:

-Cyfluthrin (Tempo, Bayer Advanced Lawn & Garden Multi-Insect Killer)

-Bifenthrin (TalstarOne, Onyx)

-Deltamethrin (Deltagard)

-Lambda cyhalothrin (Scimitar, Spectracide Triazicide)

-Esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer)

-Permethrin (Spectracide Bug Stop Multi-Purpose Insect Control Concentrate)

-Carbaryl (Sevin) **Careful this product may kill bees

For those seeking a more natural alternative, Neem products such as Azatrol or Neem-Away (Gardens Alive), or Pyola (pyrethrins in canola oil) provide about 3-4 days deterrence of Japanese beetle feeding. Additionally, there are a number of biological controls, however that is a large topic for another day! Remember, always follow labeled instructions when using any insecticide. Another popular method of 'control' for Japanese beetle is the use of a trap. Unfortunately, this is not a good control method and may actually cause more problems. Research has shown that the traps attract many more beetles than are actually caught, and susceptible plants along the flight path of the beetles and in the vicinity of traps are likely to suffer much more damage than if no traps are used at all. Lastly, there is always the option to do nothing. Typically feeding lasts 30-45 days. While they do eat a lot of foliage, most healthy trees can tolerate moderate defoliation and will recover. If your trees or plants are already stressed and not doing well then treatment may be needed. Defoliation reduces the plant's ability to photosynthesize, therefore reducing its ability to produce the energy required to fight other pathogens and issues it may be battling.

Final Thoughts

If you go out to find your plants covered in small metallic looking beetles, don't panic. Yes, the Japanese beetle invasion is here, and yes they eat a lot. Also, the good news is that there are treatment options available. First, before spraying chemicals on your landscape ask yourself a few questions. How bad is the infestation? Are they only on a few plants, or are they doing damage to all your landscape plants? How much longer will they be around? Is it worth treating at this point? Do I have stressed or struggling trees that are under attack and are in need of treatment immediately? Do I want to use a chemical or botanical treatment? All of these things must be taken into consideration. Hopefully this has helped to clarify a few things and give you a better idea of how to deal with the invaders. Remember, this will be over shortly, but if you have any questions please do not hesitate to contact us!


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