Use these tips to get rid of Japanese beetles.
Prevent Japanese Beetles From Eating Your Plants!
How to Identify Japanese Beetles
Japanese Beetles are 陆 inch in length with distinct metallic blue-green heads. They have copper-colored backs, tan wings, and small white hairs lining each side of the abdomen. Japanese beetles usually feed in small groups.
Prior to becoming adult beetles in late June, they are 1-inch-long, white, c-shaped grubs that live in the soil and feed on the roots of many plants. These grubs are often a problem in lawns.
Once adults, Japanese beetles live only 40 days, but they are voracious. Japanese beetles attack plants in groups, which is why the damage is so severe. Most feeding starts in mid-to-late June in the North and mid-to-late May in the South.
Photo Credit: .
Signs of Japanese Beetle Damage
Japanese beetles feed on a wide variety of flowers and crops (the adult beetles attack more than 300 different kinds of plants), but in terms of garden plants, they are especially common on roses, as well as beans, grapes, and raspberries. Here鈥檚 what to look out for:
- Unhealthy, Brown Patches in Lawn
First come the Japanese beetle grubs (larvae), which damage grass when overwintering in the soil. The grubs feast on the roots of lawn grasses and garden plants. This can cause brown patches of dead or dying grass to form in the lawn, which will pull up easily thanks to the weakened roots. - Skeletonized Leaves and Flowers
Then come the adult Japanese beetles which chew leaf tissue from between the veins, leaving a lacy skeleton. You鈥檒l know right away when you see leaves that are 鈥skeletonized鈥 (i.e., only have veins remaining). (Mexican Bean Beetles can also leave foliage skeletonized, though, so be sure to identify the beetle by their appearance as well.)
To manage Japanese Beetles in yards and gardens, the trick is to start early! Once these insects are present in large numbers, the problem is very difficult to manage. Here are 10 tips to prevent beetles:
- Start at the grub stage! BTG or Bacillus thuringiensis galleriae (e.g., products such as grubGONE!) uses naturally-occurring soil bacteria. This bacillus ONLY targets certain lawn insect pests, such as Japanese Beetle grubs, before they become destructive adults. The grubs ingest the spores and the natural yet powerful BTG proteins as they feed in the soil.
It is as effective as a chemical pesticide and works within days to weeks of application but is NOT toxic to beneficial insects, such as earthworms, bees, and pollinators; it will not harm people, pets, animals, or plants. BTG will kill not only Japanese Beetle grubs but also a variety of other destructive beetle larvae and grubs, such as Chafers, Oriental Beetles, and Billbugs, throughout the spring through fall seasons.
To deter an infestation of adult beetles and kill the beetles that do infest your edible or ornamental plants, you can use BTG or Bacillus thuringiensis galleriae as a spray (e.g., product beetleGONE!). Like with the grubs, BTG effectively kills the adult beetles through a combination of the BTG protein and spores. One key to success is to start applying early: at the first signs of the adult beetle. Farmers and growers have stated that they believe BTG may reduce the attraction by early-arriving beetles of more beetles by inhibiting the effectiveness of the early arrivals鈥 use of their beetle-attracting pheromones.
This product can be mixed in water and sprayed on edible garden plants, ornamental plants, and trees to kill Japanese Beetle adults or put into turf to kill the grubs. It can also be used dry as a mix into potting or garden soil to control beetle grubs. The product is registered with a zero-day pre-harvest interval, therefore, you can treat for beetles and pick your food the same day. There are no label restrictions for use around bees or flowering plants; therefore, it can be safely used while pollinators are active. There is also no toxicity to fish or aquatic life.
- Hand pick early: Look for beetles in mid-to-late June or early July. In the early morning or evening, when beetles are more sluggish, knock beetles into a bucket of soapy water. Yes, it鈥檚 time-consuming, but it鈥檚 also the most effective way to kill these pests. Just be diligent. When you pick them off, put them in a solution of 1 tablespoon of liquid dishwashing detergent and water, which will cause them to drown. Do this daily, as the chemical trail of beetles attracts more beetles.
- Protect with row covers: Use row covers during the 6- to 8-week feeding period that begins by mid-to-late June in the North and mid-to-late May in the South. Row covers will keep the pests out, but they will keep pollinators out, too; be sure to remove netting or covers if your crops need to be pollinated. Do not cover plants in bloom that require pollination (i.e., fruits); after the plant sets fruit, then cover it with netting.
- Spray Neem oil if early: Deter feeding by adult beetles by spraying plants with Neem oil, which contains potassium bicarbonate. Adult beetles ingest a chemical in the neem oil and pass it on to their eggs, and the resulting larvae die before they become adults. Neem oil is effective for several days, but repeat applications are needed, especially after rainfall. Neem oil is not effective once you have beetles in large numbers. Neem is low risk to bees and other beneficial insects but can be harmful to fish and aquatic life, so don鈥檛 use it near lakes, rivers, and water.
- Do NOT use traps. They attract beetles, but research has proven that more beetles fly toward the traps than are caught. You鈥檒l be pulling beetles in from all over town and end up with a worse problem.
- Choose the right plants: There are some that Japanese Beetles seldom damage, such as boxwood, clematis, chrysanthemum, conifers, daylily, geranium, ginkgo, Japanese tree lilac, forsythia, common lilac, magnolia, red and silver maple, oak, white poplar, redbud, rhododendron, and yew. See our list of the Best and Worst Plants for Japanese Beetles. Dispersing the beetle鈥檚 favorite plants throughout the landscape, rather than grouping them together, can also help.
- Introduce natural enemies: You can also attract native species of parasitic wasps (Tiphia vernalis or T. popilliavora) and flies to your garden, as they are predators of the beetles and can be beneficial insects. They will probably attack the larvae, but they are not very effective in reducing the overall beetle population.
- Use companion plants: Avoid attracting beetles with companion planting. Try planting garlic, rue, or tansy near your affected plants to deter Japanese beetles. (Roses love garlic is a popular expression.) All herbs and other aromatic plants make wonderful companions. Scented geraniums (Pelargonium), rue (Ruta), feverfew (Tanacetum), parsley (Petroselinum), and thyme (Thymus) all may help ward off Japanese beetles as well as aphids. Try ornamental and culinary sage (Salvia), anise-hyssop (Agastache), Russian sage (Perovskia), lavender (Lavandula), yarrow (Achillea), oregano (Origanum), catmint (Nepeta) and calamint (Calamintha). Four-o鈥檆locks (Mirabilis) and larkspur (Delphinium) are said to act as decoys by attracting rose-loving Japanese beetles to eat their poisonous leaves, but they do not kill the beetles.
- Beware of insecticides: If you wish to use insecticides, speak to your local cooperative extension or garden center about approved insecticides in your area, and be aware of whether you鈥檙e killing the very pollinators that bring fruit and flowers!
For example, Chlorantraniliprole (Acelepryn庐) provides two to four weeks of protection and is low risk to bees. But most dusts or sprays are highly toxic to honeybees, native bees, and other pollinators. If application of these materials to plants is necessary during the bloom period, do not apply during hours when bees are visiting the flowers (late morning through mid-day). Apply sprays in the morning, never in full sun or at temperatures above 90潞F. If your plants start to wilt, rinse the leaves immediately with clean water.
- Nip rose buds and spray rose bushes: Note that insecticides will not fully protect roses, which unfold too fast and are especially attractive to beetles. When beetles are most abundant on roses, nip the buds and spray the bushes to protect the leaves. When the beetles become scarce, let the bushes bloom again. Timeliness and thoroughness of application are very important. Begin treatment as soon as beetles appear, before damage is done.
For rose growers, see our Growing Guide for Roses for more tips on caring for roses!
Photo Credit: Jeff Hahn, University of Minnesota.
Catherine Boeckmann
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Research suggests that the beetles are most active on warm, sunny days between the hours of 9 AM and 3 PM but they also may feed at night.
Japanese beetles seems to enjoy eating my amaranth plants. So we can add amaranth to the list. (Amaranth is known to farmers as pig weed.)
Has anyone found peppermint oil an effective deterrent?
Back in 2009, a study was published that had looked into how well various essential oils helped to repel Japanese beetles. Wintergreen was the best, followed by peppermint oil; a combination of the two were even more effective. These weren’t foolproof (some years yielded better results than others), but they were better than other essential oils at repelling Japanese beetles from traps baited with an attractant.
Wondering if you spray the lawn with these essential oils does it kill the beetles before the season they come up from the ground?
for some reason my room is filled with those bugs and i can't get rid of them
I use a shop vac to vacuum up Japanese beetles off my plants. Adding pieces of PVC pipe as an extension to the tubing lets you reach up high. Try different sizes of vacuum attachments to get suction enough to grab beetles with little damage to the plant. It's very emotionally satisfying to pour bleach on several gallons of beetles at one time, die beetles!! :) Wonder how many beetles are in a gallon?
And if you do the tarp trick mentioned in the article, do it when it's chilly before dawn, as soon as they warm up they will start flying. Sweep them off the tarp and into a can often, so if it warms up a degree or so and they start flying, they don't get away.
I have considered using a shop vacuum but was afraid that it might make the vacuum stink, what's your experience?
I have elderberries that Japanese Beetles seem to really relish. Insecticidal Soap did a fair performance controlling them. However they would come back fairly soon and even before the next rain. Neem Oil did a much better and longer control on them. They stayed away until the next very hard rain which is not exactly common in my part of Arkansas in the deepest throes of summer. Like the article says hand picking (Which I do) is great method, however, when you have 50 elderberry plants that can get pretty tedious. I was literally picking quarts of them a day before using Neem oil. Filling a five gallon bucket a week. In my 50+ years, my particular site here in North Central Arkansas had never seen them until three years ago.
Thanks so much for your suggestion of the Neem oil. I just discovered the beetles for the first time ever today. They were enjoying my large pots of Hibiscus, my most treasured flowers! Then I saw them on my Knockout rose bush devouring one bloom. A minimum of 6 were chewing away, crawling over one another. I have a spray bottle of Neem, went right out and sprayed the heck out of the Hibiscus and rose bush, and I am now Japanese beetle free!!
