Japanese beetle

Insect

Japanese beetle

Popillia japonica Newman

Coleoptera: Scarabaeidae

Distribution: Southeastern Canada and in most fruit-growing states in eastern US.

Photos

Adult feeding on fruit surface. Peter McGhee, MSU
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Japanese beetles can be present from June through September. Japanese beetle adults are metallic green or greenish bronze with reddish wing covers and several white spots near the abdomen tip and along the sides. They have 6 or 7 small tufts of white hair around the posterior (rear) abdomen, just under the wing covers. Japanese beetles are active during the the day and feed on many species of trees, shrubs and flowers, sometimes causing serious damage to roses, linden trees, grapes and others. Adults are known to feed on over 300 species of plants, although some are preferred over others. Eggs are laid in late July and August. The eggs hatch in about 10 days and the small (1/8 inch long) grubs begin feeding on turf roots. Larvae are larger C-shaped grubs that live in the soil. They grow larger as they feed until late October when they are nearly 3/4 inch long. When the soil temperature cools below 50° F the grubs begin to move deeper into the soil to overwinter. The move back into the root zone and start feeding on turf roots in April, but new damage is rarely observed from Japanese beetle grubs in the spring.

Japanese beetles are often present in a mixed population with European chafer. Healthy turf can easily support a population of 5 grubs per square foot, even when not irrigated, or up to 15 per square foot where it is irrigated. Proper mowing, fertilizing and watering should be the first line of defense when dealing with Japanese beetle grubs.

Crops Affected: turf

Damage

Distant: Turf thins in patches in the lawn or in a golf course fairway; dead patches may appear if a heavy grub infestation is combined with prolonged dry weather in September or October. Skunks and raccoons may turn-over heavily infested turf in search of grubs to eat.

Up close: Turf heavily infested with grubs can be easily rolled back when most of the roots have been consumed. In the top 2 inch of soil under infested turf look for C-shaped white grubs from 1/8 to 1 inch long.

Time of year when damage appears: Normally found in mid-September and October especially after a dry spell. If numbers are high, the damage may be observed becoming worse in the spring as the grass is beginning to turn green.

Host: All grass types

Site: Japanese beetle tends to prefer irrigated turf or turf in areas receiving frequent rain in July and August. This includes golf courses, home lawns, athletic fields and recreational turf.

Description of damaging stage: 3/8 to 3/4 inch long C-shaped white grubs. They have 6 legs, a brown head capsule, and visible chewing mouthparts. They can be identified to species by the pattern of hairs on the underside of the last abdominal segment, called the raster.

Management

Sampling: Between September 1 and October 15, dig a 1 ft² area of turf down about 3 inches and sort through the roots and soil to look for grubs. Do this in several spots in the yard close to, and in, the dying patches. If the removed turf is kept moist, and watered immediately after putting it back in place, it should re-establish. Sample around the edges of dead patches of turf instead of in the center of the dead patch. If an average of 5 grubs per square foot is found in non-irrigated turf or in a golf course fairway, or if 15 or more are found in an irrigated lawn, an insecticide application may be desirable.

Preventing Pest Injury to Turfgrass: Home lawns, recreational turf and golf course roughs can be managed to avoid insect injury without insecticides by using proper fertility, mowing at a height of 3.0 to 4.0 inch, and watering during dry periods. This will build a dense stand of turf and a diverse community of insects that will keep turf pests under control. All lawns in Michigan will typically start off lush and green in the spring and will go dormant and turn brown during periods of little rain. Information on the use of insecticides to treat turf pest problems is only meant to be used for the unusual cases where turf damage from pests becomes unacceptable. Even then, insecticides should only be used in areas of a lawn with severe turf damage, and only until a dense turf is re-established.

Using insecticides: Use insecticides judiciously, temporarily, and only in response to unacceptable turf injury. Many insecticides are poisonous if ingested, and therefore must be stored in places where they cannot be found by children. Use the rate recommended on the label for the pest you are attempting to control. Wear rubber gloves, safety glasses (or goggles), rubber boots, long pants and long sleeved shirts when mixing and applying insecticides. The most caution is needed when mixing a concentrated insecticide in water, because skin contact with the concentrated insecticide in the original container is more dangerous than contact with the diluted insecticide after mixing. Water the turf immediately after applying the insecticide to wash it to the base of the plants or into the soil and allow the turf to dry before allowing access by people and pets.

Chemical Control of Grubs: There are 2 types of chemicals that can be used for grub control: curative products (carbaryl and triclorfon) and preventive products (neonicotinoid insecticides such as imidacloprid, thiamethoxam, clothianidin and the anthranilic diamide insecticide, chlorantraniliprole). Read the ingredient section of the label of the insecticide package to determine which active ingredient is in it. The chemicals listed earlier are by common name. There are a myriad of trade names that these active ingredients are in. The curative grub compounds work now (or at least in the next 7-10 days). They need to be applied at the full rate recommended for grub control and should be watered in immediately after application with a minimum of 1/2 inch of water. See the specific sections for the species of grub you are treating for. They will give about 40-65% grub reduction. Don't use these too late in the fall as it will take one to two weeks to get to where the grubs are feeding. If it is getting cool, the grubs will not be feeding and will not pick up any of the insecticide. The grubs begin to pupate between mid-May and the beginning of June, depending on the grub species. They stop feeding and again, will not pick up any insecticide if it is applied too late. It is best to wait and apply a preventive compound for a spring grub problem unless there is a very high population.

The preventive grub compounds are systemic and are absorbed by the roots and moved throughout the grass plant. It takes a while for the materials to be absorbed by the plants and they work best on small grubs. It is important to get the material into the root zone so that it can be picked up by the plant. It is also important to apply it early enough to give the chemical a chance to be picked up by the grass before the grubs become large. When properly applied they will give 90+% control of grubs. They do not kill the grubs present at the time they are applied; they kill the ones that will be developing in 3-12 weeks. Ideally, the neonicotinoid applications should be made between June 1 and mid-July and should be watered in with a minimum of 1/2 inch of water. They can be applied as late as mid-August, but it becomes more critical to supply irrigation the later you wait. The effectiveness falls off rapidly after about the 3rd week of August, even with irrigation. Chlorantraniliprole is a relatively new compound for grub control. It is much less water soluble than the neonicotinoids and therefore must be applied much earlier. April to mid-May is the optimum timing for chlorantraniliprole, followed with 1/2 inch of irrigation.
Crops Affected: grapes

Damage

Japanese beetles feed on the upper leaf surfaces, leaving a lacelike skeleton. Injured leaves may turn brown and die if feeding is severe, but clusters are not attacked. Juice grape vines are resistant and tolerate some damage, but vinifera and hybrids are more susceptible. This pest can be a problem particularly in new vineyards using grow tubes. Frequent monitoring is required to reduce the risk of severe damage. Japanese beetle traps may attract beetles to vineyards, so their use is discouraged. Beetles lay eggs underground in grassy areas near vineyards, preferring soil with moisture. The white, C-shaped larvae (grubs) feed on grass and weed roots and overwinter underground in these areas.

Management

Cultural and biological controls of grubs may reduce subsequent abundance of adults.
Crops Affected: apples, cherries, peaches, pears, plums

Damage

Attacks all tree fruits, particularly peach and apple. Adults (only) feed on the surface of the fruit and leaves of deciduous fruits (B, C). The fruit may be partly peeled and gouged in irregular shallow patches, or nearly devoured. The leaves are skeletonized (B). Damage is more severe in sandy locations, often occurring especially at orchard edges in proximity to grassy areas.

Management

Feeding damage from adults is sporadic and transient during the summer. If needed, an insecticide can be applied when leaf damage or the insects feeding on foliage are noted in the trees; retreatment may be necessary as new adults arrive. Biological control of Japanese beetle may be elected through use of milky spores of bacteria or nematode products.

Similar Species

Rose chafer [Macrodactylus subspinosus (F.)] adults are slender, long-legged beetles, fawn-colored with a reddish-brown head and thorax, and undersurface of the body black. Its larvae are also large, C-shaped grubs. Both rose chafer and Japanese beetle are relatives of green June beetle (Cotinus nitida), with whom Japanese beetle sometimes occurs in the adult stage. The two species can be distinguished by the differences in their size and coloration; also, unlike green June beetle, which can injure both green and ripening fruit, Japanese beetle prefers fruit that is close to ripe.