They’re back! Just when we thought that perhaps the harsh winter had saved us from our annual scourge of these destructive pests, they’ve arrived in their full glory, chomping our roses, grape vines and a whole range of plants!
There’s no easy way to control Japanese Beetles, but there are a few ways to lessen their impact. There are plenty of chemical-based products on the market today but unfortunately there aren’t many natural controls that are totally effective, but here are a few suggestions to try. NOTE: Japanese beetles use pheromones to attract other beetles to good eating spots, so the sooner and more diligent you are in eliminating them, the better it will be for you and your plants!
Taking matters into your own hands – literally! As disgusting as it might sound, the most effective way to deal with them once they’ve hatched is to take a wide-mouthed jar or yogurt container filled with soapy water into the garden and knock the beetles into the jar. It’s best to do this in the early morning or early evening when the beetles are in their lazy stage. Make certain that they’ve all died before tossing the water. You can add a bit of vinegar or oil into the water to hasten that process. If you have a large population and the space to do it, you can also place drop cloths around the plants, shake the beetles onto the drop cloths and then drown them in a bucket of soapy water.
Some grub controls like Milky Spore disease can lessen the grub (Japanese Beetle larvae) population within your own yard, but because these beetles can fly long distances, having a grub-free yard won’t prevent others from visiting your gardens.
We’ve found that Neem Oil is also pretty effective in controlling beetles but it isn’t a normal insecticide and won’t kill the beetles immediately. It can suffocate them but it isn’t immediate. It is more of a deterrent and also works well against other garden pests like leafhoppers, tomato hornworms and grasshoppers when used as a spray. It can also be used as a systemic insecticide whereby a dilution of Neem oil is poured into the soil around the plant and the plants then absorb it in their tissues. Insects may still try a few nibbles but they won’t be back. Caution: Neem oil is nontoxic to beneficial insects simply because those insects don’t eat your plants. However, if they’re sprayed with Neem, they too can suffocate. Neem oil sprays and concentrates can be found at most garden centers.
Insecticidal soaps can be effective in killing the beetles they come in contact with but generally don’t provide any ongoing protection to the plants themselves. They tend to be a bit expensive but you can even make your own natural insecticidal soap using cedar oil.
Diatomaceous earth (often referred to as DT earth) has also been touted as a way to kill Japanese beetles. This white talc-like powder is the fossilized remains of tiny aquatic organisms and when sprinkled on pests, destroys them. We’ve used DT earth (food grade only – available online and at many feed stores), to control flea beetles, slugs, snails, ants and other garden pests and it makes sense that it could also work on Japanese Beetles, especially if it gets under their hard, protective shells to irritate the softer part of their bodies. (Thanks to reader Cheryl Arthur who’s brought this to our attention!)
Beetle Traps – don’t do it! If you’ve seen traps filled with Japanese beetles and been impressed with their effectiveness, keep this in mind: these traps release chemicals called pheromones into the air to lure the beetles. Yes, this is the same method that beetles use to attract other beetles. The result? Beetles from meadows, woodlands, and your neighbors yard come to your garden to see what’s happening! So, you’re not really killing the ones you already have in your yard, you’re attracting more! If you must use them, place them as far away from your garden as possible.
Companion planting is also said to be effective. For instance, white geraniums are touted as Japanese beetle deterrents and may even be poisonous to them. We gave it a try this year, planting them around our Flower Carpet Yellow roses and haven’t seen a sign of the beetles on those plants. 4 O’clocks are also said to be poisonous to Japanese beetles. They love the taste but drop dead quickly after eating them. We tried some around our rudbeckia and although the 4’ O’clock leaves are being devoured, their blossoms will be fine, and the rudbeckia is untouched and the ground is scattered with dead beetles.
And finally, choosing the right plants for your garden may be the best way to handle this problem. Although roses tend to be a favorite of Japanese beetles, especially some of the modern shrub roses, with their strong breeding, Flower Carpet roses tend to be of less interest to them. That’s not to say that the beetles won’t nibble on them here and there, just as they do many other plants in the garden, but they won’t destroy or devour them. The photo below shows a Flower Carpet Scarlet planted side by side with a Knock Out Red rose and you can clearly see the difference. Although they can attack a multitude of flowers and plants, their favorites include grapes, zinnias, blueberries, evening primrose, mallow and most fruit trees.
Looking for more information? Marie Iannotti with About.com offers more indepth information about Japanese beetle controls and life cycles. Iowa State University’s extension service also offers very helpful advice.
Have you been successful in controlling Japanese beetles without the use of harmful chemicals? If so, please share your tips in our comments section below and thanks to all who have suggested additional ways to control these pesky beetles!