Identification and Life Cycle Figure
The damage from Japanese beetle feeding on corn and soybean can be eye-catching, especially on field edges. Japanese
beetles have a large host range and can feed on corn silks potentially reducing pollination and kernel set and cause
defoliation in soybean. Mild winters and early planting generally contribute to higher Japanese beetle populations.
Adult Japanese beetles (Popillia japonica) are about 5/16 inch (8 mm) long, have a metallic green head and neck region,
reddish to bronze wing covers, a row of six white bristle bunches along each side of their abdomen, and live about 30 to
60 days (Figure 1).1 The adults emerge from the soil starting in late May and early June with peak emergence occurring
four to five weeks later. Mating, which occurs soon after emergence, causes the females to burrow two to four inches
(51-102 mm) into the soil to lay four to six eggs every three to four days for several weeks. Eggs take roughly two
weeks to hatch into small grubs (larva).1 The grubs are 0.5 - 1.2 inches (13 – 30.5 mm) in length depending on the
instar, typical white, and C-shaped and similar in appearance to other commonly found white grubs. Larva are easily
identified by a V-shaped arrangement of hairs (raster) adjacent to the anus. Japanese beetle grubs may heavily infest an
area, however, a heavy white grub infestation is not always an indicator of potential severe injury from adult beetles,
as the beetles are very mobile and can move large distances to locate a preferred food source.
Figure 1. Japanese beetle feeding on soybean leaf.
Corn Scouting and Thresholds
The adults feed on pollen, tassels, silks, and leaves. Corn leaves may appear skeletonized or “lacy”, but leaf feeding
is rarely of economic importance. Economic damage can occur when beetles prevent pollination by early silk clipping. It
is important to protect silks during the first five silking days. Silk clipping after pollination does not affect yield
potential. When silks are clipped during pollination, this can interfere with pollination and the ears may be only
partially pollinated (Figure 2). A representative portion of the field should be evaluated when scouting corn for
Japanese beetles as populations could be overestimated if sampling is only conducted near field edges where Japanese
beetles can congregate. An insecticidal treatment should be considered during corn silking stage if:
- There are three or more Japanese beetle adults per ear, and
- Silks have been clipped to less than a 1/2-inch (13 mm), and
- Pollination is less than 50% complete, and
- Japanese beetles are still present and actively feeding.2
Figure 2. Japanese beetles feeding on corn silks.
Photo courtesy of Daren Mueller, Iowa State University, bugwood.org.
Soybean Scouting and Thresholds
Although Japanese beetle feeding can cause major defoliation, soybean plants can compensate for the damage and
defoliation is unlikely to affect yield potential (Figure 1). Flowering fields should be scouted for Japanese beetles
and the extent of defoliation. The percent defoliation should be estimated on randomly selected leaves in at least five
different areas of the field. An insecticide application should be considered if:
- 30% defoliation occurs prior to bloom or
- 20% defoliation occurs after bloom, and
- Japanese beetles are present and actively feeding.2
Foliar applied insecticide control
Damage from Japanese beetles can add to other stresses the crop is experiencing, and economic thresholds may need to be
adjusted if plants are under moisture stress.1 This, along with commodity prices, should be taken into consideration
when using thresholds to determine if insecticide treatment is needed (Table 1). Insecticide recommendation for foliar
applied adult control is an option when the population exceeds the control level for the crop. The type of insecticide
approved and the rate of application for the insecticide can be different for corn or soybeans.
|Table 1. Products labeled for control of Japanese beetles in corn and soybean in Ontario Canada.3
|Chemical Group (IRAC)
||imidacloprid + deltamethrin
|**Product is not labeled for use in this crop
This chart is based on PUB 812 for Ontario and check Provincial registrations for additional recommendations.
Foliar applied insecticides may initially control or knock-down a population; however, poor residual activity and the
mobility of the insect could lead to the need for a second application if populations resurge later. With subsequent
treatments, consider an insecticide with multiple or different modes of action (MOA).
In fields with a high risk for infestation, soil applied insecticides can also be used to target larvae (white grub) and
adults that overwinter in the soil. These chemicals include imidacloprid and halofenozide, which have been effective
against early stage larvae. Other effective active ingredients include neonicotinoids, neonics plus abamectin,
pyrethroids, organophosphates, pyrethroids plus organophosphates, and diamide seed treatments.4 White grubs feed on seed
kernels and destroy germinating seeds. In some Provinces, for some insecticide seed treatments, approval is needed on a
case-by-case situation. The producer will need to follow and respect the laws and rules of their province. It is
important to find out about local laws before buying treated seed. For more information, contact your local seed dealer.
Cultural control methods include irrigation during peak flight periods and adding more organic matter to the soil. This
can help with controlling beetle populations by making it more difficult for the adult beetle to deposit eggs in the
field. Biological controls include nematodes, parasitoid wasps, and bacteria have been identified as chemical control
alternatives but are currently very expensive.4
Performance may vary from location to location and from year to year, as local growing, soil and weather conditions may
vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts
of these conditions on the grower’s fields.
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