Beetles return to terrorize gardens

Metallic insects attack lawns from larval stage through adulthood

Adult Japanese beetles are metallic green with bronze wings. Although it seems like they are everywhere all of the time, they only live above ground for about one month of the year. Adult Japanese beetles feed on leaves and petals, leaving the veins to form what appears to be a skeleton. (Submitted photo / Joe Boggs, OSU Extension)

The beetles are here and I’m not talking about the Fab Four. On the recent check of my gardens, I discovered Japanese beetles on my hops, zinnia and rose plants.

Japanese beetle (Popillia japonica) is one of a few beetles that cause damage in both adult and larval stages. The adult is one of the most hated insects in the garden. It skeletonizes leaves and petals leaving them to appear lacelike. This feeding leaves the veins, after the consuming a large amount of tissue between the veins.

Adults are metallic green with bronze wings and are 1/2 inch oval shaped. Although it seems like they are everywhere all of the time, they only live above ground for about one month of the year.

Larvae are C-shaped white grubs that live in the soil. It is a type of white grub that feeds on organic matter, grass roots, as well as roots of trees, shrubs and vegetables. It is among the most damaging pest of your turf. Their presence encourages animals like skunks, moles and crows to dig up these juicy grubs for a quick meal. If you find small holes in your turf, this is the most likely cause of the damage.

Natural enemies include various parasitic wasps and diseases such as milky spore (Bacillus popilliae), which takes attention to detail for it to be effective. Several traps are sold to control Japanese beetles. The research data shows that traps are not effective for control. Actually, they can draw more adult beetles to your yard — causing even more damage to their favorite plants.

So I guess this is OK to give to a not-so-friendly neighbor? But, in all seriousness, they are not worth your money or time.

Personally, my favorite beetle control is to put soapy water in a bucket then knock the beetle into the bucket. The soap breaks the surface tension of the water so the beetles will go under water. I do this in the morning before they get too active.

The eggs and young larvae must have water, or they dry out and die. Thus, avoid irrigation during the time you see adults. With this dry weather, we may see a decline in populations next year.

Insecticides should be the final choice for control but may be needed to protect highly affected plants from feeding beetles. There are different options available for different uses, but the most effective options are directed at the grubs.

Japanese beetles spent winter in the soil as nearly full-grown grubs. They move below frost line during the coldest months. As soil warms, grubs resume feeding on grass roots and pupate below the surface.

Adults generally emerge in late June or early July at 970 growing degree days. They feed on foliage, and mate, returning to lawn areas near sunset. Females lay eggs in small masses in soil cavities the dig 2 to 4 inches deep. Most eggs are laid mid-August. Japanese beetles have a one-year life cycle.

For details on this insect and a list of trees/shrubs to avoid (because they are favored by the beetle), visit http://go.osu.edu/japanesebeetles

Paytos is an Ohio State University Mahoning County Extension Master Gardener volunteer.


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