Native to Japan, the Japanese beetle (Popilia japonica) was first detected in New Jersey sometime around 1916. It has since spread to nearly every state east of the Mississippi, and continues to spread each year. The adult beetles are skeletonizers, which means they feed on the leaves of trees by eating the tissue between the leaf veins. Severe Japanese beetle infestations can completely devour all of the tree's leaf tissue, leaving only the veins behind. They will often feed on flowers and fruit as well.
Japanese beetle attacks a broad host range of shade trees, shrubs and other woody ornamentals, grape vines as well as fruit and vegetable plants. Soil applications of Xytect or Lepitect will provide acceptable levels of stand-alone control.
Use of a calendar of growing degree days (GDD) is very helpful in forecasting the timing of treatments. Japanese beetle adults typically show up at 1000 GDD, and finish up their feeding season around 2100 GDD. Consult your Territory Manager or local Extension office for further information on using growing degree days as part of your pest management strategy.
Protecting trees against early feeding is extremely important.Japanese Beetles are attracted to trees that are being fed on by other beetles.Applicationof Acelepryn just prior to anticipated arrival of adult beetles allows for treatmenton trees which may happen to be in flowering stage, without undue risk to pollinating insects visiting the trees. Studies have shown effective control for several weeks with foliar applications of Acelepryn. A second foliar application of Acelepryn or a soil application of Lepitect will be necessary to extend control throughout the active season of feeding, which typically lastsuntil at least 2100 growing degree days.
For heavy infestations, combine a soil application of Lepitect or Xytect (non-flowering species) and at least one foliar spray treatment immediately after petal drop. This will provide a high level of protection for the earliest stages of Japanese Beetle adult feeding.
Xytect 10% or Mectinite can be used as tree injection treatments for trees that cannot be treated with foliar sprays or other systemic options.
Other Treatment Practices
- When the soil applied systemic products (e.g. Xytect or Lepitect) are applied, the beetles are not prevented from feeding, but they do die after they feed. Some defoliation should be expected even on treated trees. From a distance trees will look fine, when viewed up close you will see some damage.
- Combine soil applications with foliar spray applications for clients with low tolerance for leaf damage or in areas that have a history of severe infestations.
- Feeding adult beetles attract more adult beetles to attack.
Signs of Damage
- Individual leaves are missing leaf tissue between the leaf veins causing a lacelike skeleton appearance
- After being “skeletonized” the leaves soon wilt and die
- From a distance, severely attacked trees appear as if they have been scorched by fire
- The adult is a 3/8 inch (8-11 mm) long beetle with a metallic green head and thorax, and copper-brown wing covers
- The adult beetle has a row of five white hair tufts projecting from under each wing cover and two more at the rear tip of the abdomen (this characteristic distinguishes Japanese beetles from other beetles with similar color traits)
- The larvae are white, C-shaped grubs about 1/16 inch (1.5mm) at first instar
- At maturity, the larvae are 1 ¼ inch (32 mm)
- Grubs can be significant turf pests
Photo: leaf damage
Photo: leaf damage
Photo: canopy symptoms
Photo: turf damage from grubs
Trees At Risk
Japanese beetles attack over 400 species of plants including many trees and shrubs such as linden, crape myrtle, flowering crabapple, Norway maple, pin oak, Japanese maple, flowering cherry, elm, sycamore, black walnut, horse chestnut, plum, gray birch, and others.
- The larvae overwinter in the soil at a depth of 4-8 inches.
- Adult emergence occurs over a 3-4 week period during late June through August, or earlier on southern portions of the country (GDD 1056. Just as petals fall on linden trees). Upon emergence, adults release pheromones that attract other beetles.
- After mating and feeding on leaf tissue for a few days, the females lay 1-5 eggs into the soil and return to the tree to start the feeding, mating, and egg laying cycle over again.
- The females will lay about 40-60 eggs by the end of these cycles.
- The eggs hatch in 8-14 days where the larvae feed on roots and organic material before overwintering.
Journal of Arboriculture and Urban Forestry
Chlorantraniliprole: Reduced-risk Insecticide for Controlling Insect Pests of Woody Ornamentals with Low Hazard to Bees; Carl T. Redmond and Daniel A. Potter, ISA Journal of Arboriculture & Urban Forestry 2017. 43(6):242–256
University of Minnesota
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.