Natural Solutions for Keeping Japanese Beetles at Bay

Ready or not, the Japanese beetle will return (again and
again). This beetle critter is a serious pest. The adults, which typically
emerge in late June and early July, attack more than 300 plants. The beetles are
about 3/8-inch in length. The front of the beetle is dark metallic green and the
wing covers are a metallic dark tan. Look for five white hair tufts along each
side of the dorsal abdomen. Nice and pretty, but pretty nasty.

With our unusually warm, early spring, look for them around
the middle of June.

Other beetles may look similar, such as the False Japanese
beetle, the Rose Chafer, and the May/June beetle, for example. But only the
Japanese beetle has the distinctive white hair tufts and the metallic green and
dark tan body.

You can welcome the Japanese beetle to your yard if you have
trees such as the American linden, American mountain ash, apply, cherry,
flowering crabapple, Norway Maple, apricot, peach and plum trees. You say you
don’t have those trees in your yard? Not to fret, for they will gladly attack
your roses, grapes, Virginia creeper, blackberry, raspberry, hollyhock,
honeysuckle, iris, lilies, peonies and zinnias. Look for the adults on your
Canna leaves and in the flowers of your dahlias. They will also eat the leaves
of your peas, beans, basils, cantaloupe, cucumbers, tomatoes, potatoes and a
host of other plants.  

The beetles overwinter as larvae/grubs in the soil. They burrow about 10 inches below ground and a quite adaptable to a Minnesota winter. The grubs are cream colored and are “C-shaped.” The grubs eat grass roots. It is a beetle that keeps on giving! 

Do you have grubs in your lawn now? Not sure? Look for patches of dead grass. You can roll back the sod like a carpet to expose the grubs. Are you a little squeamish about doing that? Not to worry, because as the grubs come closer to the surface, around April and May, you may see holes in your grass. The grubs are not doing this, but animals that eat them, such as starlings, crows, moles, shrews and skunks are partial to the grubs and create these holes looking for a tasty meal.

Japanese beetles eat the leaf matter between the veins. They start in the middle of the leaf, not the edges.

Prevention. If possible, consider alternative plants for your yard. Arborviate, black oak, boxelder, common lilacs, euomymus, fir trees, green ash, junipers, pine trees, red maple, red oak, rhodendron and White Ash are some better choices.

You can apply insecticides to your lawn between the middle of May through the middle of August. These insecticides can prevent the grubs from becoming a serious problem for your lawn. However, if your favorite neighbors fail to do this the adults will fly into your yard and garden from not just your neighbors’ yard, but from miles away. The males are attracted to the female pheromone. Females live for a few weeks, feed on your plants in the morning and lay their eggs in your lawn in the afternoon. This goes on for as long as they are alive.

While applying insecticides such as Imidacloprid, Ethoprop, Malathion or Halofenozide (e.g., Merit, Mocap, GrubEX) can help they also can be highly toxic to birds, fish and bees such as honeybees and bumblebees. During a heavy rain, the runoff can adversely affect ponds, lakes and rivers, so be careful about applying insecticides. Think about these negative consequences before you purchase them.

Setting traps is not a good idea at all. Japanese beetle traps include the female pheromone, which attracts the males by the hundreds. Generally, the traps will attract more beetles to your yard than what is “normal.”

A better, safer and more reliable method is to use a bucket of soapy water. I use a 5-gallon bucket with about 2-3 inches of water and a liquid soap that you would use to wash dishes. Catching these critters in the morning or late afternoon is best. Place the bucket below the infected plant and simply knock them into the soapy water. They will be dead within about 30 seconds. This is very effective and non-toxic to birds, bees, fish or water sources. 

You can hand spray the water-soap mixture directly on the leaves, but be careful. Too much soap and your leaves will burn and turn brown. So, experiment before you use this method.

For your vegetables, a floating row cover or netting may help. You can purchase these materials at your favorite garden center and fabric shop. However, there can be draw-backs with these covers, especially if that vegetable needs bees and other insects for pollination. The netting can keep out the Japanese beetles, but they can also prevent the pollinators from doing what your plant requires, pollinate to produce the fruit or vegetable.