Things You'll Need
Japanese beetles are a hated scourge. Adult beetles ruin ornamentals and vegetables by eating flowers, tender stems and leaves, often leaving a characteristic, skeletonized leaf. The grubs bore into the ground and eat plant roots all summer. Telltale signs of grub damage are reduced plant vigor in summer and large patches of dead grass. The gardener looking for a pesticide to minimize Japanese beetle populations will find a friend in carbaryl, known by the trade name Sevin. Sevin is favored, especially in vegetable gardens, for its non-toxicity to both humans and plants.
Mix Sevin with water in a spray container according to the manufacturer's directions. Sevin is available as a powder or liquid concentrate and also comes in a ready-to-use spray bottle.
Spray the tops and bottoms of plant leaves, all buds and flowers and the stem and branch parts of the shrub. The plant should be dripping with the milky solution. When the leaves dry, they will have a light, powdery film that will wash off in the rain.
Reapply every two or three weeks until Japanese beetle adults become less active in late summer. Monitor the plants for beetle presence and damage between applications. Fast-growing plants such as roses and vegetables may need more frequent applications as they produce fresh, unprotected plant parts.
Water affected lawn areas thoroughly to increase penetration of the active ingredient into the soil.
Apply Sevin to the lawn, following manufacturer's directions for rate of dilution and volume of application. The grass should be evenly wet and dripping with the liquid.
Water again thoroughly after application. Watering increases the efficacy of Sevin by moving it into the soil, where the grubs feed on grass roots.
Begin spraying plants when adult beetles and their damage can be observed. Repeat applications every two to three weeks until the adults disappear in late summer.
Begin spraying lawns as soon as grubs begin feeding on turf roots--about two weeks after the first appearance of adults. Starting early kills grubs when they are small and actively feeding. Reapply every two to three weeks until Japanese beetle grubs slow down in early fall.
You can use a hand-held spray bottle or pump sprayer. Hose-end sprayers are useful for application on large areas of lawn.
Don't spray areas of turf that are not affected by Japanese beetle grubs. Overuse can kill beneficial and benign insects and grubs, making room for Japanese beetles to do their damage.
Robert W. Lewis
Robert Lewis has been writing do-it-yourself and garden-related articles since 2000. He holds a B.A. in history from the University of Maryland and has training experience in finance, garden center retailing and teaching English as a second language. Lewis is an antiques dealer specializing in Chinese and Japanese export porcelain.