The Japanese beetle can be a destructive pest of trees, plants and turf. It is important to understand that an IPM (Integrated Pest Management) program will not eliminate all Japanese beetles from your property; however, the management options discussed here can help you reduce the damage inflicted by this pest.
To control the Japanese beetle, several potential tactics are available. The choice of method will reflect the management objectives and control philosophy of the homeowner.
In order to plan and implement appropriate control strategies for the Japanese beetle, you must first survey your property for both grubs and adult beetles.
Traps for adult beetles operate primarily with 2 chemical lures. A combination of a pheromone, or sex attractant, and a floral lure attract both male and female adult beetles to the trap. Then, as a result of their clumsy flying and the design of the trap, they end up caught in either the bag or funnel portion of the trap.
Assessing Japanese Beetle Population Density Japanese beetle traps can be used to assess the beetle population in a given area. For instance, if you put a trap out while the adults are flying and find that beetles fill the trap in 1 day, you probably have a serious Japanese beetle problem. If, during a week, the bottom of the trap is barely filled, you probably do not need to be concerned. Adult beetles can fly long distances, so those caught in your yard may have come from up to a mile away. For this reason, it is difficult to estimate the number of grubs in your turf from adult trap catches.
To survey for grubs, you need to calculate the number of Japanese beetle grubs per square foot in your lawn. This estimate is important for deciding the severity of your white-grub problem and whether treatment is necessary.
Japanese beetle grubs can be sampled in late summer (August to October) and late spring (April to June). Timing will vary by geographic location.
If your lawn has brown or dead areas, survey near the edge of the damage. If you find that grubs are the cause of the damage, clearly this area should be treated. Otherwise, take several randomly selected samples throughout the lawn. The density of Japanese beetle grubs often varies widely within a small area, so by taking several samples, you may be able to pinpoint the damage and therefore selectively treat specific areas rather than the whole lawn.
Using a shovel, dig a square hole 8" x 8" x 3" deep in the turf. Turn the sod over on some newspaper and search the grass roots and the soil in the hole for grubs. Turn the turf back into the hole and add water to help the grass recover. Record the number of grubs found in the sample location so you can map out or average grub densities. To convert these numbers to the number of grubs per square foot, multiply them by 2.25. Generally, you should consider treating areas in your lawn with more than 10 grubs/square foot.
If you have a serious Japanese beetle infestation, you probably already have seen the damage. You need a plan of action. There are several methods that can be used and it is perhaps best to use combinations of these methods. Make no mistake, these beetles can quickly strip a desirable plant in a matter of days. Ignoring the infestation can leave your valuable plants at risk.
If you have seen Japanese beetles already eating your plant to shreds, perhaps the best course is to spray the leaves with an insecticide that lists Japanese beetles. Sevin is a good example. Insecticidal soaps are not effective at controlling the Japanese beetle.
Set out a beetle trap upwind of where the insects are feeding.
After the insects disappear, apply a grub control to the lawn and landscape beds. This will not only protect your lawn from damage, but will also slightly reduce the population next year.
Homeowners who decide to use chemical methods in an IPM approach to Japanese beetle management should base their decision on several factors. Choosing what pesticide to apply and when to apply it comes down to a value judgment for the individual. First, you must assess the risks and benefits of pesticide use. Correct timing and application are probably the most essential elements for success with pesticide applications. Because pesticides are toxic materials, users must read and follow label directions exactly!
Each state has its own agricultural chemicals handbook, updated yearly for appropriate control recommendations. The following chemicals are effective for use in the control of the Japanese beetle adult and its grubs:
Chemicals for Adults:
Carbaryl
Malathion
Methoxychlor
Rotenone
Chemicals for Larvae (grubs):
Imidacloprid (Merit Insecticide for turf; Marathon for nursery use)
Bendiocarb
Isofenphos
Chlorpyrifos
Diazinon
These lists do not include all materials registered for Japanese beetle control. For further details regarding chemical controls, consult your local Cooperative Extension Service. Before using any of these chemicals, check the label for particular formulations registered for Japanese beetles, read the entire label, and carefully follow application instructions regarding dosage and rate.
Be aware that all insecticides are extremely dangerous, especially if you have children and pets. Consider the risks before applying any insecticide Ask yourself: is that plant worth more than the health of your children, pets and yourself? Maybe it would be better to just replace the plant with something that is less attractive to these destructive pests.
When used improperly, insecticides can pose serious hazards to people, wildlife, and the environment. There is also increasing concern about the fate of insecticides in the environment and the potential for pesticide runoff to cause water contamination. Because of these concerns, scientists believe that biological control agents are preferable to pesticides in the suppression of turf insects.
Homeowners who choose biological methods to control Japanese beetle populations can successfully use parasites, nematodes, fungi, or other biologically based approaches. Some of these agents are commercially available to homeowners; others are not. While they take a little longer to produce the same results as insecticides, biological control agents last longer in the environment. More importantly, they do not adversely affect non-target insects, or more important, potentially beneficial organisms that live in our landscapes.
Biological controls are used primarily for grub control. While these controls will greatly reduce the grub population in your lawn and the resulting damage they can cause, they will do little to control adult Japanese beetles. Once the Japanese beetle emerges from the ground, it will seek out other Japanese beetles and a desirable food source. Therefore if you have a desirable food source, they will find it.
Insect-eating nematodes, microscopic parasitic roundworms, actively seek out grubs in the soil. These nematodes have a mutualistic symbiotic relationship with a single species of bacteria. Upon penetrating a grub, the nematode inoculates the grub with the bacteria. The bacteria reproduce quickly, feeding on the grub tissue. The nematode then feeds on this bacteria and progresses through its own life cycle, reproducing and ultimately killing the grub.
The 2 nematodes most effective against Japanese beetle grubs are Steinernema glaseri and Heterorhabditis bacteriophora. The latter is commercially available.
When using nematodes, remember they are alive and have a fairly high oxygen requirement. They are typically sold on a carrier, which they can survive on for 1 — 2 months under cool conditions. They can be applied with any standard insecticide applicator. Once mixed with water, nematodes must be applied fairly quickly. Follow accompanying directions carefully for best results.
Nematodes may be purchased in lawn and garden shops or through biological mail-order catalogs.
Bt is a naturally occurring soil bacterium typically used as a microbial insecticide. The Bt strain registered for the Japanese beetle is for use on the grub stage only. Bt is a stomach poison and must be ingested to be effective. Apply it to the soil as you would insecticides. Effectiveness is similar to that of insecticides. Check with your extension agent regarding the availability of Bt.
Milky spore is the common name for spores of the bacterium Bacillus popilliae. This bacterium was first registered for use on turf in suppression of the Japanese beetle grub in the United States in 1948.
Upon ingestion, these spores germinate in the grub's gut, infect the gut cells, and enter the blood, where they multiply. The buildup of the spores in the blood causes the grub to take on a characteristic milky appearance.
Milky spore disease builds up in turf slowly (over 2 — 4 years) as grubs ingest the spores, become infected, and die, each releasing 1 — 2 billion spores back into the soil. Milky spore disease can suppress the development of large beetle populations. But it works best when applied in community-wide treatment programs. Check with your extension agent regarding the availability of milky spore material.
Releasing natural enemies or parasites of an exotic insect is a successfully proven method to reduce pest populations. Introduced parasites must be shown to be host specific (that is, to parasitize only the target pest) before USDA approves releasing them. Two such parasites of the Japanese beetle have been brought to the United States from Asia. Researchers have successfully established these insects in areas inhabited by the Japanese beetle, and the parasites are now functioning as important biological control agents of the beetle.
Tiphia vernalis, a parasite of the Japanese beetle grub, and Istocheta aldrichi, a parasite of the adult, have been shown to be important in regulating the population dynamics of the beetle in the Northeastern United States.
These parasites are not yet commercially available; however, you can contact your local extension agent to see if they are established in your area. If they are, planting the appropriate food plants will attract these parasites and increase the rates of parasitize, and thus help control the Japanese beetle on your property.
Tiphia vernalis: This small, parasitic wasp of Japanese beetle grubs resembles a large, black, winged ant. Its current distribution is believed to be throughout the Northeastern United States and south to North Carolina.
After a brief period of feeding and mating during the spring, the female wasp digs into the soil, paralyzes a beetle grub by stinging, and then deposits an egg on the grub. When the egg hatches, the emerging wasp larva consumes the grub.
Food sources for Tiphia vernalis: Adult wasps of this species feed almost exclusively on the honeydew of aphids associated with the leaves of maple, cherry, and elm trees and peonies. In North Carolina, the nectar of tulip poplars has been found to be an important food source for the adult wasps.
Istocheta aldrichi: This solitary fly is an internal parasite of the adult Japanese beetle. The female flies are capable of depositing up to 100 eggs during a period of about 2 weeks. The eggs are usually laid on the thorax of the female beetles. Upon hatching, the maggot bores directly into the beetle's body cavity, killing the beetle.
Because it does not take this fly long to kill the beetle, I. aldrichi can suppress Japanese beetle populations before beetles can reproduce.
Food sources for Istocheta aldrichi: I. aldrichi is commonly seen feeding on aphid nectar deposited on Japanese knotweed (Polygonum cuspidatum), a persistent perennial weed native to Japan.
Birds in the yard will also eat the beetles. However, depending on this as a means of control is not reliable. The number of beetles that would attract birds will be significantly more than the birds can consume.
Making the habitat less suitable for Japanese beetles is another way of controlling their populations over the long run. Cultural methods typically employed in the control of the Japanese beetle include planting resistant plant species and using mechanical traps designed to attract and trap the adult beetles.
Diseased and poorly nourished trees and plants are especially susceptible to attack by beetles. Therefore, keep your trees and plants healthy. Also, prematurely ripening or diseased fruit is very attractive to beetles. Remove this fruit from the trees and the ground. The odor of such fruit will attract beetles, which are then in a position to attack sound fruit.
Although the Japanese beetle feeds on almost 300 species of plants, it feeds sparingly or not at all on most plants. The various kinds of plants on your property can significantly influence the susceptibility of your property and plants to Japanese beetle damage. Having a well-dispersed mixture that favors non-preferred species can reduce the level of beetle-caused damage.
When beetles are abundant, damage to plants can be minimized by using species that are immune to, or seldom attacked by the insect. When planting a new ornamental or modifying established plantings, make more extensive use of trees, shrubs, and other plants that are not preferred by the beetle. Select plants that are least likely to be seriously injured. Use the following list as a guide for determining what plants to cultivate on your property, and what plants to stay away from.
While these lists apply in most situations, they may not ALWAYS apply. A recent reader related his problem that had recently planted a Euonymus alatus that was devoured by an onslaught of Japanese beetles which devastated his plant.
Every landscape situation is unique. Plants listed as being resistant to Japanese beetles means just that: they are resistant. Under the right situation (heavy infestations, lack of other nearby food sources, etc.) any plant can become a food source, and a reminder that whenever you notice Japanese beetle damage, remove the insects by hand as quickly as possible to prevent further damage.
| Plants Resistant to Adult Japanese Beetle Feeding |
|
|---|---|
Primary plants that are resistant to adult beetles:
|
|
| Magnolia | Magnolia sp. |
| Redbud | Cercis sp. |
| Dogwood | Cornus sp. |
| Red maple | Acer rubrum |
| Northern red oak | Quercus rubrum |
| Burning bush | Euonymus alatus |
| Holly | Ilex sp. |
| Boxwood | Buxus sp. |
| Hemlock | Tsuga sp. |
| Ash | Fraxinus sp. |
Secondary plant list:
|
|
| False cypress | Chamaecyparis sp. |
| Yew | Taxus sp. |
| Juniper | Juniperus sp. |
| Arborvitae | Thuja sp. |
| Spruce | Picea sp. |
| Pine | Pinus sp. |
| Forsythia | Forsythia sp. |
| Lilac | Syringa sp. |
| Clematis | Clematis sp. |
| Sweetgum | Liquidambar styraciflua |
| Plants Susceptible to Adult Japanese Beetle Feeding |
|
|---|---|
Primary plants that are top of the menu for the beetles:
|
|
| American linden | Tilia americana |
| Crabapple | Malus sp. |
| Apple | Malus sp. |
| Japanese maple | Acer palmatum |
| Norway maple | Acer platanoides |
| Rose | Rosa sp. |
| Crape myrtle | Lagerstroemia sp. |
| Pin oak | Quercus palustris |
| Birch | Betula sp. |
| Plum, Apricot, Cherry, Peach |
Prunus spp. |
Secondary plant list:
|
|
| Black walnut | Juglans nigra |
| Willow | Salix sp. |
| Grape | Vitis sp. |
| Horsechestnut | Aesculus hippocastanum |
| Althea | Althea sp. |
| Asparagus | Asparagus officinalis |
| Highbush blueberry |
Vaccinium corymbosum |
| Sassafras | Sassafras albidium |
| Virginia creeper | Parthenocissus quinquefolia |
| Summersweet | Clethra sp. |
Millions of beetles are captured annually in mechanical traps. This method is an easy and inexpensive way to reduce beetle populations and curtail egg laying. Under favorable conditions, a trap will capture only about 75% of the beetles that approach it. Because the traps actually attract more beetles than they capture, be sure not to put traps near your garden or your favorite plants. Put traps at the borders of your property, away from plants the beetles may damage. Traps are most effective when many of them are spread over an entire community.
Homeowners who choose to give the mechanical traps and lures a try as part of their IPM program can typically find them at yard and garden centers.
Traps should not stay in place year 'round because the lures inside get stale. Trap placement should be timed to coincide with the emergence of adult Japanese beetles in your area. Adults generally emerge between early June and late August. Check with your extension agent for information of the Japanese beetle flight period in your area.
Shaking the tree Another method of controlling large numbers of Japanese beetles is to go out very early in the morning when these pests are less active. Place a large plastic sheet underneath the plant being attacked. Then vigorously shake the plants to dislodge the beetles. Because of their sluggishness at this time, most will not be able to fly off and they will fall to the ground. Quickly fold up the plastic sheeting to trap the beetles and then dispose of the beetles in such a way that they cannot return.
