Japanese beetles have been with us here in the Central Great Plains now for almost 10 years. However, they have become more of a problem in the last 6, with western expansion from the Missouri River areas. And because they are now present and not going away, we have to learn how to manage them in a way that keeps them from overwhelming us. Its going to be tough for organic gardeners like myself too because the farmers feel like they need to spray more insecticides to reduce beetle populations and damage on corn, soybeans, and other crops.
But what ways as a homeowner can we manage Japanese beetles without turning to full out chemical warfare? When we too turn to chemicals, we kill of more than just the beetles, but every predator and beneficial insect as well. We have to turn to the predators, as well as cultural controls for management. But first we need to go over again all we know about Japanese beetles.
Where Did Japanese Beetles Come From?
Well, they came from Japan. How did they get here? In 1916 the City of New York hosted the World’s Fair. And because of that, they had to bring in materials from all over, including iris bulbs from Japan. It is surmised that the iris bulbs has Japanese beetle larvae or eggs hiding on their roots, and they escaped into the nursery they were sent to. Why did we not torch the area then?
It is likely that several thousand iris roots were brought over, not just a few, and therefore several thousand Japanese beetle larvae or eggs. Moving them into the soil at planting would have been accidental, but entirely possible. And even though they have adapted to our country, it has taken them a century to get to and past the Missouri River, the longest river in the United States.
They are now spread across the country, but not established fully in every state. See the map below.
Life Cycle
Japanese beetles begin as eggs laid in sod in either turf or pasture in July. The eggs hatch in August and the newly hatched grubs begin root feeding in September. Sometime in October, the grubs move downward into the soil for overwintering (this is likely based on a reaction to soil temperature). The grub stays deep in the soil until April, as the soil begins to warm and root development begin anew. They feed from April to June, then pupate and emerge as adults in early June and July. The adults feed for 6 to 8 weeks, mate, and lay eggs and the process starts over again.
What do They Eat?
The grub stage of the beetles feed on the roots of turfgrass and other grasses in pastures and meadows. While many homeowners prefer to use grab killers such as Merit (Imidicloprid) in the soil, this route would only work if everyone was doing it. But if your neighbor does not use a grub killer, and you do, all you are doing is preventing grub predators (skunks, moles, raccoons, opossums, etc.) from eating in your yard.
The adult beetles feed on a variety of plants and fruits aboveground. They cause damage mainly to tree leaves and fruit, but also flowers. In severe infestations, they can defoliate trees from the top downward. Plants which they prefer include:
- Fruit trees, especially plum, apricot, cherry, peach
- Littleleaf linden
- Elm
- Grape
- Hibiscus (all types)
- Birch
- Crabapple
- Mountain Ash
- Roses
- Oakleaf hydrangea
- Common milkweed
But, just because they prefer these plants, does not mean that they will not eat other plants too.
Look-A-Likes
Japanese beetles have several look-a-likes, mostly other beetles. At the grub stage, there are a lot of other beetles, and only an expert can identify them. But in the adult stage, there are several similar beetles. Japanese beetles how 2 rows of white hair tufts on the abdomen, 1 on each side. This is the main distinguishing factor. See the photo below for look-a-likes.
Controlling Japanese Beetles
There are variety of ways in which we can control or limit the populations of Japanese beetles in our landscapes and gardens. We must first start with promoting biodiversity, as natural predators are our first line of defense against them. If we can continue to add native plants, reduce or eliminate pesticides and synthetic fertilizers, and let natural processes run, then we will build a wall of protection for ourselves.
Natural Predators
The first step in managing them is to know your natural predators. For every pest there is a solution, whether its insects, mites, arachnids, fungi, birds, or animals. Despite the Japanese beetle being an invasive species, there are many native predators which have adapted to eating it. Birds and mammals are the largest predators. Robins, starlings, crows, sparrows, cardinals, blue jays, wild ducks, turkeys, and others all eat beetles. Among mammals, coyotes, raccoons, opossums, moles, and others eat the beetles, as adults and larvae. A
Arthropods which eat Japanese beetles include:
- Ground beetles
- Tiger beetles
- Wheel bugs
- Predatory stink bugs
- Assassin bugs
- Spiders
- Rove beetles
- Tachinid flies
- Introduced parasitoid wasps
How to Attract Natural Predators
To get more predators of Japanese beetles, and other pests in you garden, you need to first eliminate the use of insecticides, most fungicides, and synthetic fertilizers. All those things damage the ecosystem and deter arthropod populations from making the yard a home. Plant natives, as many as possible into your yard and garden. And add pollinator plants which provide either pollen or nectar, or both for insects that are playing multiple roles (pollinator and predator). The following is a short list of plants which provide food for predatory insects:
- Queen Anne’s Lace
- Milkweeds
- Coreopsis
- Roughleaf Dogwood
- Daisy Fleabane
- Rattlesnake Master
- Bonesets
- Joe-Pye Weed
- False Sunflower
- Mountain Mints
Trapping
One of the ways in which I have lessened the effect of Japanese beetles in my own landscape is with the use of traps. In the past, we have been warned off about traps because in areas where they were first arriving, the traps attracted beetles in from other areas. But now that they are widespread, trapping is an effective method to remove beetles from the garden.
But not just a single trap will do. And you have to empty them daily. For an acre yard I would recommend at least 3 barrel traps. These can be done in 2 ways:
- Use a barrel with a small amount of soapy water and is enclosed so the whole barrel fills up after a few days (See photo 1)
- Or you can have an open barrel 3/4s full of water and scoop the beetles out every day (See photo 2) – this is the method I use because I supplement my ducks’ feed each day with Japanese beetles from the end of May to August.
By using the barrel method you can reduce the feeding damage to plants by at least 50% over the 6 to 8 week feeding period. But the key with traps is to place them on the edge of the property, and put them out before the adult beetles have emerged (end of May is best time).
Handpicking
This is another way in which you can selectively remove beetles from plants. The best time of day to do this is early morning before they start warming up. Carry a bucket (5 gallon works best) with soapy water in about 1/3 of it, and gently scoop or push the beetles into it. If you shake a plant covered in the morning, they will usually fall off into the bucket. Be sure not to squeeze the beetles however, when handpicking, becuase other beetles are attracted to the scents released when squished.
Exclusion
What do I mean by exclusion? Basically, it means to use insect netting to keep beetles of important plants or crops. This can work as long as you keep the netting tight and only use netting which is made to exclude insects (bird netting will not work).
Pesticides As Control
These should always be the last control method used, and only in extreme situations. I do not like to use or recommend pesticides, in any form, but there are situation which warrant the use of them. If you are being overwhelmed by beetles in a commercial apple, peach, or plum orchard, I would think the best solution may be pesticides. In those instances, it many be warranted to use organic sprays first, before switching to synthetics
- Organic – Neem Oil
- Organic – Insecticidal Soap
- Diatomaceous Earth – Organic
- Bifenthrin – Synthetic
- Imidicloprid – Synthetic
- Milky Spore – Organic
- Bt for Beetles
Conclusion
Japanese beetles are around and here to stay (unless a miracle happens). We must use the best possible measure for controlling them in our landscapes, measures that protect our ecosystems and our children as well.
Happy planting!
