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Like it or not, we will be visited by Japanese Beetles again this summer. Introduced to our eastern coast decades ago, they have been munching in our direction ever since. Assisted by climate change, Japanese Beetles have adapted to our winters and will now be an annual adversary.
As disheartening as it can be to watch the devastation of lawns, roses, birch trees, grape vines and raspberry patches to name only a few, be assured that, unless plants are seriously stressed for some other reason, the Japanese Beetle attack will not kill your garden treasures. We may never eradicate these voracious and destructive pests, but there are some satisfying things we can do to minimize their numbers.
Japanese Beetles are about the size of your little fingernail. They are easily identified by their iridescent green-bronze wing covers and the six small tufts of white hairs along each side. They are serious pests in both the adult beetle and the larval grub stages. Adult beetles will eat almost any plant, though they do have preferences, skeletonizing leaves to a lace work. They are above ground, feeding, mating and laying eggs from perhaps mid June to early August. Be aware that they can fly! The white ‘C’ shaped grubs spend most of the rest of the growing season eating the roots under your lawn, resulting in brown patches that increase in size with time. Fortunately there is only one brood each year.
One organic method of control is to simply hand-pick them. Hold a small bucket of strong soapy water under the bug and tap or shake the critter into it. You will need to be diligent about this, visiting your plants as often as possible and inspecting carefully. Several times each day is best. You may find that children (who often find Japanese Beetles ‘pretty’) can be persuaded to assist with this if suitable reward is offered.
Another organic method is to cover your plants with a physical barrier such as fine-mesh screening fabric. Light-weight spun bond coverings (aka ‘floating row cover’ or ‘seed covering’) are available for this purpose at your favorite Garden Center (Linder’s!). While this method is not practical for very large plants such as trees, it can work well for a favorite rose or specific veggies. Be sure whatever covering you use is ’breathable’ to allow moisture and as much light as possible to pass through. Remove the covering as soon as Beetle season is over. Do NOT use plastic.
One of the most efficient methods of reducing Japanese Beetle numbers is to treat your lawn for grubs. There are both organic and chemical products available. Although killing grubs under the lawn this summer will not affect the number of beetles this year, their numbers next year may be reduced.
‘Milky Spore’ is a biological agent that is specific to Japanese Beetle grubs; it does not harm earthworms, other insects such as bees and butterflies, pets, humans or other animals. It does need one or more applications annually for three to five years to adequately inoculate your lawn, but once appropriate levels are in place, no further treatment is needed for as much as 10 years. While Milky Spore may be a bit less effective here than in southern states due to our shorter season, grubs are less likely to thrive where Milky Spore is present.
A granular insecticide can be applied to lawns to kill Japanese Beetle grubs. The annual version is a good preventative to have in place when the female Japanese Beetles are laying eggs in the lawn in mid-summer. Baby grubs are most vulnerable in late summer and early fall while they are still small and near the soil surface. You will also find a short-term grub killer to use when grubs are visible in large numbers just under the lawn surface.
There are several insecticides available to use for adult Japanese Beetles. A liquid systemic such as Imidachloprid (Merit) absorbed through plant roots can be useful for very large plants and trees. Topical insecticides can be sprayed directly on plants and range from organic insecticidal soaps and Neem products to permethrin and contact insecticides. If you are spraying edible plants, be sure the product is labeled for those plants. Be aware, however, that these are ‘broad-spectrum’ insecticides that affect many kind of insects, including bees and butterflies, so use them cautiously, applying only when and where needed. Keep these insecticides away from ponds and streams as well.
Traps for adult beetles have become controversial: some professionals feel they don’t work. In fact, the problem is that they work too well, sometimes attracting more beetles than are captured. On the other hand, trapped beetles are not eating your roses or laying eggs under your lawn to produce next year’s generation of pests, and are easily dispatched. If you choose to use traps, be sure to place them well away from whatever plants you are trying to protect.
Whether and how intensely you choose to do battle with Japanese Beetles is up to you. There are likely to be some in your garden no matter what you decide; they are able to fly in from your neighbor’s garden or the golf fairways across the street. Your plants are likely to survive one way or the other. However, such destructive pests need not be encouraged! The knowledgeable staff at Linder’s Garden Center can help!