By Debbie Barber, Portage County Master Gardener Volunteer
Every summer about this time, Japanese beetles descend upon our communities and begin to skeletonize leaves, flowers and fruits of many different plants. Some of their preferred plants include grapes and roses; linden, apple and cherry trees; basil, raspberries, hollyhocks and marigolds; and just about anything else they find. These pests are polyphagous, which means if they can’t find their favorite foods, anything will do. They can devour leaves on an entire tree in a single day during a peak infestation.
Many homeowners will rush to their local garden store and buy those big, green Japanese beetle traps and put them on the edge of their yards, hoping to fill them up with all those little green bodies. Don’t do this! Not only do the traps attract beetles in your yard, but also those in the entire neighborhood. This can worsen the infestation, not diminish it.
Let’s look at methods for lessening the impact of the devastation these pests can cause without endangering beneficial insects in your yards:
Japanese beetle scouts will appear around the end of June or first part of July. There are other phenomena occurring that help predict their arrival. Using a scientific practice known as phenology, we are able to determine fairly accurately when the scouts will arrive. In our area, look for first blooms on American elderberry, Littleleaf Linden, Southern Catalpa or Spirea, then begin to watch for the beetle scouts.
They tend to appear on the tops of leaves and should be easy to spot. Once they determine that they have located a good feeding ground they will release a pheromone, which is a chemical signal to other Japanese beetles that the feast is ready. You want to catch the scouts before the dinner invitation goes out. The best time to monitor these scouts is early morning and early evening, when it is cooler and they are lethargic. Take a jar of soapy water and knock them into the liquid.
There are interesting biological controls to consider:
– You may find evidence of Japanese beetle grubs eating your grass roots when you find brown patches in the spring. One way to try to reduce them is to let the ground dry out, provided that Mother Nature doesn’t have other ideas. Certain critters such as crows, grackles and skunks, as well as voles and moles, will feed on these grubs. There are also grub insecticides available. IPM Case Study: Japanese Beetle
– Plant peonies. They attract a parasitic wasp known as Tiphia vernalis, which will seek out the beetle grubs and paralyze them, then lay eggs that will hatch and eat other Japanese beetle grubs in the ground.
– Another beneficial insect is the winsome fly, which parasitizes the female beetle by laying eggs on its body which will eventually hatch and devour it from the inside. To attract this fly, plant umbellifer plants such as coriander, dill and yarrow. Plant Flowers to Encourage Beneficial Insects; The Fly That Attacks Japanese Beetles
Finally, there are chemical controls. It is always important to consider the impact of garden chemicals on beneficial insects, birds and other wildlife. Healthy and mature plants and trees can typically tolerate Japanese beetles and will recover without drastic measures. Fruits and vegetables can be severely affected, however.
Should you choose to use chemical controls, please read and follow the label directions for application and use. And remember: The label is the law.
It’s time to start watching for those scouts. Whatever your approach, please consider the environment and the importance of protecting our beneficial insect friends.
For more information: Japanese Beetles OSU Fact Sheet
Ohio State University Extension Portage County Master Gardener Volunteer program. Questions/comments/suggestions/want to find out more/become a PCMGV: 330-296-6432 • OSU PCMGV web • [email protected] • FB PCMGV • PCMGV Speaker’s Bureau
