Japanese Beetle Time

Its July 4th weekend and the Japanese Beetle adults have emerged from the soil and will be mating and eating the foliage of many garden plants and ornamentals. July 4 is an average emergence date in the Ohio, Pennsylvania area. It may be different where you are.

Japanese Beetles spend about 11 months of the year below ground as a larvae called a grub. They pupate for about a month then emerge as adults. The life cycle may vary slightly within an area due to differences in temperature and moisture due to microclimates. Thus, you may find Japanese Beetle adults for more than 1 month, the typical length of time for an adult.

There are various ways to protect your garden plants and ornamentals from Japanese Beetle adult feeding. One way is called exclusion, or barrier. This is simply putting a netting of screening over your plants that a Japanese Beetle can not penetrate.

If Japanese Beetles are heavy in your area, you might want to use plants that are not well liked by Japanese Beetles and remove or avoid plants they like. For example, I have a Purple Sand Cherry that Japanese Beetles love. They also are attracted to blueberries, roses and grapes. Plants that are loved by Japanese Beetles will need extra work and monitoring to protect from extensive damage.

I won't discuss sprays for Japanese Beetles. Consult your local lawn and garden supplier of County Extension Office for pesticide recommendations. One trick that I learned long ago from an old timer is to keep a large soup or coffee can or bucket with some water with liquid dish soap in it. Walk around your infested plants and knock the adults into the can or bucket. The dish soap makes the water "wetter" by breaking surface tension of the water. The beetles hit the water and drown rather quickly due to the surfactant activity of the dish soap. A surfactant is really a "surface active agent". It is something that changes the characteristics of the water. Surfactants in dish soap loosen food particles by making the water "wetter".

One can buy Japanese Beetle bags. These bags attract adult male Japanese Beetles due to a pheromone lure. Pheromones are "sex"scents given off by the female adult Japanese Beetle in order to attract males for mating. Yes, placing a bag in your garden or lawn will attract male Japanese Beetles from your surrounding neighbor's lawns, trees, and garden. Hopefully these added visitors to your property will find their way into the bag where they become trapped. If they don't, they may find your blueberries, grapes, roses, or purple sand cherries.


The following tables are by Lee Townsend, Extension Entomologist University of Kentucky College of Agriculture.

Plant Selection

Careful selection of plant species when replacing or adding to your landscape is the key to avoiding an annual battle with Japanese beetles. Certain common landscape plants are inevitably attacked and may be poor choices where this insect is abundant (Table 1).

Table 1. Landscape plants nearly always severely attacked by adult Japanese beetles
Scientific name	Common name
Acer palmatum	Japanese Maple
Acer plananoides	Norway Maple
Aesculus hippocastanum	Horse chestnut
Betula populifolia	Gray birch
Castanea dentata	American chestnut
Nibiscus syriacus	Rose-of-Sharon, Shrub Althea
Juglans nigra	Black walnut
Malus species	Flowering crabapple, apple
Platanus acerifolia	London planetree
Populus nigra italica	Lombardy poplar
Prunus species	Cherry, black cherry, plum, peach etc.
Rosa species	Roses
Sassafras albidum	Sassafras
Sorbus americana	American mountain-ash
Tilia americana	American linden
Ulmus americana	American elm
Ulmus procera	English elm
Vitis species	Table Grapes

Plants which grow rapidly and are especially attractive to the beetles are most difficult to protect. Roses unfold quickly and are especially attractive to beetles. When beetles are abundant, nip buds and spray to protect the leaves or cover the roses with netting to keep beetles out.

Beetles are fond of certain weeds and non economic plants such as bracken, elder, multiflora rose, Indian mallow, sassafras, poison ivy, smartweed, wild fox grape and wild summer grape. Elimination of these plants whenever practical destroys these continuous sources of infestation.

Many common trees and shrubs are relatively less attractive to the beetles and using them can reduce the annual frustrations of the beetle season (Table 2).

Table 2. Landscape plants relatively free of feeding by adult Japanese beetles
Scientific name	Common name
Acer negundo	Boxelder*
Acer rubrum	Red maple
Acer saccharinum	Silver maple
Buxus sempervirens	Boxwood
Carya ovata	Shagbark hickory*
Cornus florida	Flowering dogwood
Diospyros virginiana	Persimmon*
Euonymus species	Euomymus (all species)
Fraxinus americana	White ash
Fraxinus pennsylvanica	Green ash
Ilex species	Holly (all species)
Juglans cinerea	y Butternut*
Lirodendron tulipifera	Tuliptree
Liquidamar styraciflua	American sweetgum*
Magnolia species	Magnolia (all species)
Morus rubra	Red mulberry
Populus alba	White poplar
Pyrus communis	Common pear
Quercus alba	White oak
Quercus coccinea	Scarlet oak
Quercus rubra	Red oak
Quercus velutina	Black oak
Rhododendron species	Rhododendron
Sambucus canadensis	American elder
Syringa vulgaris	Common lilac
Most evergreen ornamentals, including Abies (fir), Juniperus, Taxus, Thuja (arbovitae), Rhododendron, Picea (spruce), Pinus (pine) and Tsuga (hemlock) are not attacked.
*Unmarked species undergo little or no feeding. Species marked with an asterisk may suffer occasional light feeding.