The Japanese Beetle

The Origin and Impact Of The Japanese Beetle

The Japanese beetle (Popillia japonica), originally native to Japan, has become an invasive species in the United States. Minnesota is one of the many states where the Japanese beetle is considered a firmly established pest.

Both as grubs (the larval stage) and adults, Japanese beetles are damaging plant pests.

The larvae of Japanese beetles (grubs) develop in the soil, where they feed on the roots of plants and grasses. Even in its larval stage, the Japanese beetle is capable of causing damage. As grubs, these insects destroy turfgrass in lawns, parks and golf courses.

The Japanese beetle is the most widespread turf-grass pest in the United States. Efforts to control

the insect, both in its larval and adult stages, cost more than $460 million in 2015. As the pest has spread, the costs continue to rise.  Japanese beetles can disperse by flying. Additionally, adult beetles can be moved on plant material, and larvae can be transported in the soil of nursery stock.

Adult Japanese beetles are indiscriminate about what they eat - feeding on grassroots, foliage, flowers, and fruits of more than 300 different ornamental and agricultural plants. Adult beetles feed between June and August and may cause property owners and tree care experts to worry about the pests extreme foliage consumption.

The adult beetles consume plant matter between leaf veins, giving leaves a skeletonized look. In the least impactful scenario, the Japanese beetle visibly decimates foliage, from which the plant will eventually recover. The worst case is one where the Japanese beetle causes irreparable damage to the tree.

Identifying The Japanese Beetle

The adult Japanese beetle is slightly less than half an inch long, making it about half the size of an American quarter. The males usually are somewhat smaller than the females. The beetle has a shiny, metallic-green body with bronze-colored outer wings. The beetle also has six small clusters of white hair along the sides and back of its body under the edges of its wings.

The Lifecycle and Visibility of The Japanese Beetle

Although the Japanese beetles have the lifecycle of one year, adult Japanese beetles are most likely to be seen from late spring through midsummer.

During the feeding period, June to August females periodically leave the plants they consume to burrow approximately 3 inches into the turf and lays a few eggs. This cycle of feeding and egg laying repeats until the female produces 40 to 60 eggs.

By midsummer, the eggs hatch, and the young grubs begin to feed off the roots of turf, or plants. Each grub is about an inch long (a little bigger than an American quarter) when fully grown. In late fall, the larvae burrow 4 to 8 inches into the soil where it remains inactive over the winter.  The Japanese beetle spends roughly ten months of the year within the ground in the larval stage.

In early spring, the grubs return to the turf, where they continue to feed on roots until late spring. In late spring the larvae change into pupae. Within about two weeks, the pupae become adult beetles. At this point, the mature Japanese Beetle surfaces from the ground, and the cycle repeats.

How Property Owners Can Make Informed Decisions About Treating The Japanese Beetle

While the Japanese Beetle is here to stay, there are options for managing the pest.

The first task is to survey your property for both grubs, the second is to seek professional pest treatment.

Step 1: Survey For Japanese Beetle Larve

The objective of surveying for Japanese beetle larvae is to calculate the number of beetle grubs per square foot in your lawn. This estimate is important for assessing the severity of your pest infestation, and determining 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 based on the temperature in the Twin Cities, and across the local geographic regions.

Expert Tip:  If your lawn has brown or dead areas during the normal growing season, survey near the edge of the damage. If you find that grubs are the cause of the damage, unquestionably you should book treatment.

Take several random turf samples from your lawn. Taking multiple samples is important: the distribution and density of Japanese beetle larvae grubs differ widely within a small area.  By taking several samples, you may also be able to selectively treat specific areas rather than the whole lawn. This saves you money and prevents unnecessary chemical application.

Step 2: Survey For Japanese Beetle Larve

The objective of surveying for Japanese beetle larvae is to calculate the number of beetle grubs per square foot in your lawn. This estimate is important for assessing the severity of your pest infestation, and determining 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 based on the temperature in the Twin Cities, and across the local geographic regions.

Expert Tip:  If your lawn has brown or dead areas during the normal growing season, survey near the edge of the damage. If you find that grubs are the cause of the damage, unquestionably you should book treatment.

Take several random turf samples from your lawn. Taking multiple samples is important: the distribution and density of Japanese beetle larvae grubs differ widely within a small area.  By taking several samples, you may also be able to selectively treat specific areas rather than the whole lawn. This saves you money and prevents unnecessary chemical application.

Instructions To Spot Check Larve

  1. Using a shovel, dig a square hole 8 by 8 by 3 inches deep in your lawns turf. Turn the sod over on some newspaper and search the grassroots and the soil in the hole for grubs.

  2. Record the number of grubs found in the sample location

  3. Turn the turf back into the hole and add water to help the grass recover.

  4. Collect the appropriate number of samples based on the size of your lawn (above). During each sample, collection repeat steps 1, 2 and 3.

  5. Calculate the average density of Japanese beetle larvae per square foot of your yard.
    Average pest density = (Total the number of large recorded at each sample site) / The number of samples collected.

  6. Convert these numbers to the number of grubs per square foot, multiply them by 2.25.

  7. Generally, you should consider treating areas in your lawn with more than 10 grubs per square foot.

Step 2: Hire A Professional To Treat Pest Infestation

Timing and precise application of pesticides are the two most critical factors in the chemical treatment of pests, like the Japanese beetle.

Pesticides are toxic materials: users must read and follow label directions precisely. When used improperly, insecticides can pose serious hazards to both people and wildlife. For this reason, it is best to hire a professional plant health care expert to treat pests.

Reach out to the Birch Tree Care team today for a free quote.