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Japanese Beetles

The summer season brings more than hot temperatures and humidity toNorth Carolina.  Warmer days heat soil temperatures and wake up everyone’s favorite garden pest, the Japanese beetle.  Japanese beetles can be incredibly damaging to many of our garden ornamentals.  They eat away the leaf tissue between the veins of the leaf, leaving skeletonized shells behind.  Beetles also munch on flower tissue itself, particularly crepe myrtles, roses, rose of sharon, and other summer flowering shrubs and perennials.  The extent of their damage is not limited to just the summer months, or by the insect in the adult (beetle) stage.  During both the larval and grub stages, these insects can wreak havoc on lawns by devouring the root systems of turf grasses.  The best way to control Japanese beetles is by understanding the lifecycle of the insect, and treating at the proper time with the proper product.

The adult stage of the Japanese beetle is by far the most popular.  They usually emerge from the soil around the last week of May, and persist through July and into August.  Japanese beetles are easy to identify due to their metallic green head and brown body.  They are usually found in mass on or around plants.  The females release a sex pheromone that attracts males.  In the afternoon, the females burrow into the soil and lay one to five eggs.  They repeat this cycle until they have laid around sixty eggs.  These eggs usually hatch in August to form white grubs.  These grubs are commonly found in the garden when digging a hole or even moving stepping stones or pots that have been in one spot for a long period of time.  Grubs are generally white (shaped like a “C”), with an identifiable head and a dark rear end.  During the fall months, grubs will eat the roots of lawns causing brown patches.  Grubs then burrow deeper into the ground for the winter months.  Warm spring days awaken grubs from their winter dormancy.  They rise close to the surface of the ground to feed on grass roots, causing more damage to the lawn.  As the grubs mature, they pupate and eventually turn into an adult beetle which will emerge from the ground and begin the cycle all over again.

There are several different ways to avoid issues with Japanese beetles.  The most efficient way to control these insects is by killing the grubs before they become beetles.  This is accomplished by applying grub control products to lawn and garden areas.  Bayer produces two grub control products, a 24 hour grub killer and a season long grub control product.  The 24 hour killer should be applied to lawn and mulch areas during the months of the year when the insects are in the grub stage of their life cycle.  October through April would be most effective.  The season long grub control can be applied at any time of the year, and will actually last for an entire year.  Another way to control grubs is by using Milky Spore.  The active ingredient in Milky Spore is a naturally occurring bacterium which only affects Japanese beetle grubs.  Milky Spore is most effective when applied during the spring, summer, and fall for two years.  After these initial applications, the bacteria can sustain itself for ten years.  It is an environmentally friendly way to help control Japanese beetles.

If the grub control products are not used, targeting the adult beetles is the only way to try to reduce the damage to gardens.  Two different types of sprays can help.  Systemic products like the Bayer Advanced 12 Month Tree & Shrub Insect Control can be beneficial.  This product is a systemic, meaning that the chemical is absorbed by the plant, and distributed throughout the plant by the vascular system.  If a beetle eats any portion of a plant treated with this product, it will die.  Other sprays like Sevin or Bayer Advanced Rose and Flower Insect Killer work on contact.  The downside to these sprays is that they are not selective.  They will kill other insects as well as the beetles.

We still get a lot of questions about Japanese beetle traps.  One thing is for sure about the traps, they kill beetles.  The traps use pheromones to attract the beetles, and they come in hoards.  The question is do you want to attract thousands of beetles to your beetle trap, on your property?  A Japanese beetle trap would be a great Christmas gift for one of your “favorite” neighbors down the street.  WAY down the street.  By understanding the life cycle of these insects, we can effectively treat for them and keep our gardens happier and more beautiful in the process.

Happy Gardening!

Brad Rollins