Landscape and Turf - Japanese Beetles

Japanese beetles are emerging across the state. The following is more information.

Japanese beetles are emerging across the state. Adult activity typically occurs between 1094-2410 GDD (base 50). They are highly mobile and feed on over 300 different types of broad-leaved plants. Last year JB adult populations declined in some locations with drier weather in July. Leaves are skeletonized by beetles feeding in between leaf veins. Preferred plants include roses, cannas, flowering crabapple, lindens, Norway and Japanese maples, and elms.

Many natural enemies attack JB life stages such as: assassin bugs, parasitoids, ants, ground beetles, rove beetles, birds, skunks, and raccoons. Cultural control includes hand removal, removing beetle-damaged leaves, or shaking beetles into buckets of soapy water.

Control adults with insecticides including Orthene, Sevin, or one of the pyrethroids (e.g., cyfluthrin, deltamethrin, etc.). Apply insecticides every 1-2 weeks when adult activity is high. Neem based products typically deter feeding for 3-4 days, although some report longer activity. Last year, we reported wettable powder formulations of some pyrethroids (pyrethrins) may be more repellent than EC formulations. Thorough coverage is required. Insecticidal soaps, plant extracts, and companion plantings are generally ineffective. Since adult beetles are mobile, control of white grubs or adult JB does not ensure control of the other life stages. Treat for white grubs using preventive products such as Merit or Mach 2 in mid-June to mid-July. Acelepryn is a new product with a different mode of action than Merit and may be applied as early as May for effective grub control.

Information from Brian Kunkel, Ornamental IPM Specialist, UD.