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Extension offers Japanese Beetle advice

Extension offers Japanese Beetle advice

July 10th, 2013 in News

Japanese beetles numbers are headed up.

Mid-Missouri is about three weeks later than last year.

So, Japanese beetles probably will peak at the end of July.

Below is a fact sheet prepared by James Quinn, regional horticulture specialist for the University of Missouri Extension.

"Understanding Japanese Beetles and Its Control Options"


The Japanese beetle (Popillia japonica Newman) is a highly destructive plant pest that can be very difficult and expensive to control. Feeding on grass roots, Japanese beetle grubs damage lawns, golf courses, and pastures. Japanese beetle adults attack the foliage, flowers, or fruits of more than 300 different ornamental and agricultural plants.

The Japanese beetle (Popillia japonica) is about 1/2 inch long with a shiny metallic-green body and bronze-colored outer wings. The beetle has a row of five lateral tufts on each side and one each on the last segment of the abdomen.

Japanese beetles were first found in the United States in 1916 near Riverton, New Jersey. Since then Japanese beetles have spread throughout most states east of the Mississippi River. However, partial infestations also occur west of the Mississippi River in states such as Arkansas, Iowa, Kansas, Minnesota, Missouri, and Oklahoma.

The Cole County Extension Center has had a population monitoring trap for the beetles since 2009. When first started 200 beetles in a trap for a week was peak. In 2012 the same trap caught up to 3,000 in a day. What will happen in 2013 is difficult to say; the drought last summer may have held them back and the cool and wet weather has been correlated to lesser numbers of cucumber beetles (a common vegetable pest). But they will be sure to arrive in substantial numbers. It has been reported that after about 5 to 7 years of "pest levels' that Japanese beetles seem to then drop off. Hopefully this will occur in Jefferson City region soon, but until this happens, home gardeners may need to be proactive to protect plants that these beetles find desirable. Unlike cucumber beetles which will always show up to feed on plants in the cucumber/melon/squash family, Japanese beetles are erratic and may be unpredictable on what they choose to feed on from year to year.

First emergence of Japanese beetles is about the first of June. Based on prior years they can be expected to increase for the next 4 to 5 weeks before declining for about 3 weeks. Fourth of July tends to coincide with the height of their activity.

Control of Japanese beetles is complicated, because the grub stage lives in the soil, with lawns being a favorite place. The adults feed on plant leaves, and have high preference for specific plants. Control options include treating the soil, plant foliage or mass trapping. A critical component on the control, understands IF you have a plant or plants that are a favorite food of theirs, and then IF you want to spend the time and resources to protect that plant(s), or just want to tolerate the damage for a month or so.

Favorite Plants of Japanese Beetles

Woody Plants Susceptible to Adult Japanese

Beetle Feeding


  1. Japanese maple Acer palmatum

  2. Norway maple Acer platanoides

  3. Crape-myrtle Lagerstroemia indica

  4. Apple, crabapple Malus spp.

  5. Virginia creeper Parthenocissus quinquefolia

  6. Plum, apricot,

cherry, peach Prunus spp.

  1. Pin oak Quercus palustris

  2. Sassafras Sassafras albidum

  3. American

mountain-ash Sorbus americana

  1. Linden (American,

European) Tilia spp.


  1. Horse-chestnut Aesculus hippocastanum

  2. Althaea Althaea spp.

  3. Birch Betula spp.

  4. Summer-sweet Clethra spp.

  5. Hawthorn Crataegus spp.

  6. Beech Fagus grandifolia

  7. Black walnut Juglans nigra

  8. Larch Larix laricina

  9. Lombardy poplar Populus nigra var.

  10. Willow Salix spp.

Herbaceous Plants Susceptible to Adult Japanese

Beetle Feeding


  1. Hollyhock Alcea rosea

  2. Dahlia Dahlia spp.

  3. Hibiscus Hibiscus moscheutos

  4. Common mallow Malva rotundifl ora

  5. Evening-primrose Oenothera biennis

  6. Soybean Glycine max

  7. Pennsylvania

smartweed Polygonum pensylvanicum

  1. Rose Rosa spp.

  2. Grape Vitis spp.

  3. Sweet corn Zea mays


  1. Clematis Clematis spp.

  2. Gladiolus Gladiolus spp.

  3. Sunflower Helianthus annuus

  4. Morning-glory Ipomoea purpurea

  5. Cardinal fl ower Labelia cardinalis

  6. Peony Paeonia spp.

  7. Asparagus Asparagus offi cinalis

  8. Rhubarb Rheum rhabarbum

  9. Red raspberry Rubus idaeus

  10. Zinnia Zinnia spp.

Controlling Japanese Beetles Numbers or Damage

Hand Control and Netting

Unfortunately for many individuals, these two control options will either be too time consuming, and for netting, too expensive as well.

? Hand picking can be used for small numbers of beetles. For larger numbers, some individuals like to use buckets or pans of soapy water and they then knock the plants such that the beetles fall into the soapy solution. The soap plugs up the breathing pores of the insect and they suffocate. Another hand control tactic is to use a vacuum of some type, be it a sump vac, dust buster, house vacuum, or leaf blower with reversed air flow. A strong vacuum can be hard on plant foliage so one would need to experiment some with the plant and vacuum devise.

? Netting is effective but time consuming to apply and somewhat expensive. Bird netting is not fine enough to exclude the beetles. Window screening is the least expensive screen readily available to home gardeners that is effective. For some plants that are highly attractive to birds and Japanese beetles (e.g. grapes) it could serve two purposes. Japanese beetles will be relatively easy to exclude with netting, as compared to birds and wildlife (like raccoons) which may be very persistent or cunning in circumventing netting.


Synthetic or conventional insecticides are likely to be the most easy and cost effective way to effectively control Japanese beetles.

Several over-the-counter and commercial insecticides are labeled for adult and larval (white grub) Japanese beetles.

? Carbaryl (Sevin) is effective for both adults and grubs. It is widely regarded as giving the most obvious and immediate knock down or kill of the adults. Since carbaryl provides only 1 to 2 weeks protection, frequent reapplication will be needed during heavy pressure.

? Products containing pyrethroids such as cyfluthrin (Bayer Advanced Lawn & Garden Multi-Insect Killer), bifenthrin (Hi-Yield Bug Blaster; Bug-B-Gon MAX® Lawn & Garden Insect Killer), lambda-cyhalothrin ( Spectracide Triazicide), and permethrin (many manufacturers & formulations), will provide 2 to 3 weeks protection. The criticism of these products is the adults don't appear readily killed; they get groggy and may go away or hang around.

? Systemic products (neonicotinoids) like imidacloprid (e.g. Bayer Advanced products) and thiamethoxam (Meridian) offer a good option and will provide protection for 3 weeks if not much more (check label). How they are recommended for control on roses is the most telling with roses. Bayer advises to apply at the onset of Japanese beetle emergence. If beetle damage becomes apparent, then apply carbaryl, and reapply it whenever additional control is needed. These systemic products do not translocate well into flower petals, so control may be achieved on the foliage but not the flowers. However, remember the beetles do need to eat some plant parts in order to be killed.

Organic insecticides or foliar deterrents-

? For those wanting an organic approach, Neem products like Azatrol or Neem-Away will provide 3 to 4 days deterrence of feeding. Sequential applications of all products may be needed under extended periods of activity.

? Pyrethrum based products may provide brief knock down, but may not kill the beetles. Pyrethrum based products with the synergist piperonyl butoxide may perform slightly better. However, control will be extremely short, 1 or 2 days.

? Neem products mixed with pyrethrum may provide some better effectiveness due to the combination of knock down and deterrence.

? Kaolin clay based products (e.g. Surround) are proven to provide feeding and foraging deterrence of beetles. The clay sticking to beetles disturbs them, and thus dissuades them from staying on those plants. Unfortunately it turns the plants a chalky white color.

Note- Always follow label directions and note any precautions for bees. On food crops, follow the recommended pre-harvest interval before harvest begins.

Biological Control that is Available for Purchase

Commercially available biological control of Japanese beetles is only readily available for the larvae (grubs). Application of these products normally will not reduce the pest in the growing season in which it is applied, and may take several years to reach full impact. Furthermore, (like mass trapping) it will be more effective if instituted over an entire community. Remember that the beetles can easily fly ••• mile.

? 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 two nematodes that are most effective against Japanese beetle grubs are Steinernema glaseri and Heterorhabditis bacteriophora. The latter is commercially available. Nematodes may be purchased in lawn and garden shops or through biological mail-order catalogs.

? Bacillus thuringiensis (Bt)-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-Milky spore is the common name for spores of the bacterium Bacillus popillae. 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 to 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 communitywide treatment programs. Check with your extension agent regarding the availability of milky spore material.

Mechanical Traps

Millions of beetles are captured annually in mechanical traps. These traps are commonly sold at garden centers and similar retail outlets. 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 percent 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. Japanese beetles can fly (easily) up to ••• mile.

The bags provided with store bought traps are often insufficient in size to capture beetles over several days or a week during peak flight levels. Garbage bags or similar are sometimes used to increase the capacity. If the capture container becomes too heavy, consider positioning the trap so that the bottom will rest upon the ground to take the weight off the suspended trap. Some wildlife (e.g. raccoons and opossums) like to eat the beetles and may tear into soft plastic containers. Metal window screen can be sewn up into a long tube that they will not be able to tear through. Beetles can be killed by placing them into a freezer for several days. One can try feeding Japanese beetles to chickens or birds; they may be more desirable to birds during the winter.

Sources of information-

Managing the Japanese Beetle: A Homeowner's Handbook by USDA/APHIS

Japanese Beetles on the rise or fall, but still there. Missouri Environment and Garden (newsletter), June, 2012.

Personal Communication. Jaime Pinero, State Integrated Pest Management Specialist, Lincoln University.