|University of Kentucky Entomology|
JAPANESE BEETLES IN THE URBAN LANDSCAPE
by M.F. Potter, D.A. Potter, and L.H. Townsend, Extension Entomologists
|Table 1. Landscape Plants Likely to be Attacked by Adult Japanese Beetles.|
|Scientific name||Common name|
|Acer palmatum||Japanese maple|
|Acer platanoides||Norway maple|
|Betula populifolia||Gray birch|
|Castanea dentata||American chestnut|
|Hibiscus syriacus||Rose-of-Sharon, Shrub Althea|
|Juglans nigra||Black walnut|
|Malus species||Flowering crabapple1, apple|
|Platanus acerifolia||London planetree|
|Populus nigra italica||Lombardy poplar|
|Prunus species||Cherry, black cherry, plum, peach, etc.|
|Sorbus americana||American mountain ash|
|Tilia americana||American linden2|
|Ulmus americana||American elm|
|Ulmus procera||English elm|
|1Some cultivars (e.g. Baccata v. jackii, Jewelberry, Harvest Gold, Louisa) are relatively resistant. See Kentucky Cooperative Extension Service publication ID-68, "The Flowering Crabapple," for more information.
2Tilia tomentosa 'Sterling' and Tilia americana 'Legend' are less susceptible than other lindens.
Fortunately, many common trees and shrubs are much less attractive to Japanese beetles (Table 2). These differences in susceptibility should be considered when selecting plant species and cultivars for use in Japanese beetle-infested areas.
|Table 2. Landscape Plants Seldom Damaged by Adult Japanese Beetles.|
|Scientific name||Common name|
|Acer rubrum||Red maple|
|Acer saccharinum||Silver maple|
|Carya ovata||Shagbark hickory*|
|Cornus florida||Flowering dogwood|
|Euonymus species||Euonymus (all species)|
|Fraxinus americana||White ash|
|Fraxinus pennsylvanica||Green ash|
|Ilex species||Holly (all species)|
|Liquidamar styraciflua||American sweetgum*|
|Magnolia species||Magnolia (all species)|
|Morus rubra||Red Mulberry|
|Populus alba||White poplar|
|Pyrus communis||Common pear*|
|Quercus alba||White oak*|
|Quercus coccinea||Scarlet oak*|
|Quercus rubra||Red oak*|
|Quercus velutina||Black oak*|
|Sambucus canadensis||American elder*|
|Syringa vulgaris||Common lilac|
|Most evergreen ornamentals, including Abies (fir), Juniperus, Taxus, Thuja (arbor vitae), Rhododendron, Picea (spruce), Pinus (pine) and Tsuga (hemlock) are not attacked.
*Species marked with an asterisk may suffer occasional light feeding.
Japanese beetles are also fond of certain weeds and non-cultivated plants such as bracken, elder, multiflora rose, Indian mallow, poison ivy, smartweed, and wild grape. Elimination of these plants whenever practical destroys these continuous sources of infestation.
Although plant selection is important, other approaches must obviously be used to protect susceptible plants that are already established in landscapes.
Removing beetles by hand may provide adequate protection for small plantings, especially when beetle numbers are low. The presence of beetles on a plant attracts more beetles. Thus, by not allowing beetles to accumulate, plants will be less attractive to other beetles.
One of the easiest ways to remove Japanese beetles from small plants is to shake them off early in the morning when the insects are sluggish. The beetles may be killed by shaking them into a bucket of soapy water. Highly valued plants such as roses can be protected by covering them with cheesecloth or other fine netting during the peak of beetle activity.
Many insecticides are labeled for use against adult Japanese beetles. Examples include pyrethroid products such as cyfluthrin (Tempo, Bayer Advanced Lawn & Garden Multi-Insect Killer), bifenthrin (TalstarOne, Onyx), deltamethrin (Deltagard), lambda cyhalothrin (Scimitar, Spectracide Triazicide), esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer) and permethrin (Spectracide Bug Stop Multi-Purpose Insect Control Concentrate and other brands). Carbaryl (Sevin and other brand names) too is effective. The pyrethroid products generally provide 2-3 weeks protection of plant foliage while carbaryl affords 1-2 weeks protection. For those seeking a botanical alternative, Neem products such as Azatrol or Neem-Away (Gardens Alive), or Pyola (pyrethrins in canola oil) provide about 3-4 days deterrence of Japanese beetle feeding. Insecticidal soap, extracts of garlic, hot pepper, or orange peels, and companion planting, however, are generally ineffective.
With all products, foliage and flowers should be thoroughly treated. The application may need to be repeated to prevent reinfestation during the adult flight period. Follow label directions and avoid spraying under windy conditions or when bees are foraging. Be sure the insecticide is registered for use on the plant or crop you intend to spray. If it is a food crop, note the minimum number of days that must be observed between the date of the last application and the date of harvest.
Because Japanese beetles are attracted to favored host plants from a considerable distance, controlling white grubs in the lawn will not protect landscape plants from adult feeding.
Japanese beetle traps are sold in many garden centers. Commercially available traps attract the beetles with two types of baits. One mimics the scent of virgin female beetles and is highly attractive to males. The other bait is a sweet-smelling food-type lure that attracts both sexes. This combination of ingredients is such a powerful attractant that traps can draw in thousands of beetles in a day.
Unfortunately, research conducted at the University of Kentucky showed that the traps attract many more beetles than are actually caught. Consequently, susceptible plants along the flight path of the beetles and in the vicinity of traps are likely to suffer much more damage than if no traps are used at all.
In most landscape situations, use of Japanese beetle traps probably will do more harm than good. If you experiment with traps, be sure to place them well away from gardens and landscape plants.
Mention or display of a trademark, proprietary product, or firm in text or figures does not constitute an endorsement and does not imply approval to the exclusion of other suitable products or firms.
CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.
Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!