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Japanese Beetle Management
Rastral pattern on Japanese beetle.
Description of Stages:
The larval stage is a C-shaped white grub similar in apprearance to the June beetle, rose chafer and European chafer. The white grub lives in the soil. It's primary food source is grass roots, but it is known to feed on the roots of corn, beans, tomatoes and strawberries.
The pupae stage is where the grub starts to transform into a beetle. Japanese beetle pupae start out cream colored and age to a reddish brown. The average pupa is about 1/2 inch (14 mm) long and 1/4 inch (7 mm) wide. 
Larvae (Grub) Stage
All white gub species are similar looking but vary in their life cycles, so identifying the grub to species is important for the proper timing of Japanese beetle management options. All white grubs, including those of the Japanese beetle, are white, C-shaped, and will have six legs. In total length, the larva of a Japanese beetle will range in size up to about 2.5 cm (1 inch), making it a moderate-sized species. They can be distinguished from other white larvae by the pattern of hair on the hind end of the abdomen (rastral pattern) which forms a distinctive V-shape. First instar larvae are about 1/16 inch (1.5 mm) long while the mature third instars are about 1-1/4 inch (32 mm) long. Pupal Stage
The adults are a brilliant, metallic green color, generally oval in outline, 3/18 inch long and 1/4 inch wide. The wing covers are copper-brown and the abdomen has a row of five tufts of white haris on each side. The males have a sharp tip on the foreleg tibia while the female has a long rounded tip.
Adult Japanese Beetle
Life Cycle:
Japanese beetles lay their eggs in July and August. The eggs hatch and the young grubs begin feeding on grass roots within one or two weeks. Dry soils in July and August will casue many eggs to die from moisture stress. The grubs feed until fall and then burrow deep into the ground to overwinter. In the spring, the grubs burrow upwards to the grass root level and resume feeding until late May and then transform to the pupal stage. Adult Japanese beetles usually emerge in the beginning of July and can be found right through September. After hibernating through winter, the gurbs migrate into the turf root zone and feed again in May and June. Around mid-June, the grubs pupate, eventually emerging as adults in one to three weeks.
The Japanese beetle lives about one year, but in cooler climates can overwinter and live up to two years.The adult beetles are know to feed on over 400 species of broad-leaved plants, although only about 50 species are preferred. The grubs will also feed on a wide variety of plant roots including ornamental trees and shrubs, garden crops and turfgrasses. The adults are skeletonizers, that is, they eat the leaf tissue between the leaf veins but leave the veins behind. The adults will often attack flower buds and fruit. The grubs can kill small seedling plants but most commonly damage turf.Grub Control:
1. Since the eggs and young grubs are very susceptible to dry soils, do not irrigate during the time the eggs and first instar larvae are developing.
2. Do not plant trees and shrubs thar are highly attractive to adult Japanese beetles near turf.
3. The bacterial milky diseases have been quite effective at controlling grubs. Milky spore works best when soil temperature is between 60-70 degrees F. The spore count must build up for 2 to 3 years to be very effective especially in northern New Hampshire. During this time you should not use an insecticide against grubs that are needed to complete the baterium cycle.
Milky Spore is available in 20 pound bags and covers 7,000 square feet. This is a 2 - 3 year program with application three times per year in spring, summer and fall.
4. Beneficial nematodes are becoming widely available for white grub control. It is critical that the soil temperature be close to 70 degrees F. Apply the nematodes when the white grubs are in the second instars. Irrigation before and after nematode application with 1/4 inch of water minimum greatly increases the efficacy of the nemtodes. Nematodes "swim" through water between soil particles seeking grubs to attack.
5. Insecticides control grubs, but repeated applications may be necessary because of the relatively short rediual effect of the pesticides. Also, cautions about their use must be observed.
Product (Granular)WeightCoverage Active Ingredient Comments/Cautions
WeightCoverage Active Ingredient Comments/CautionsAdult Japanese Beetle Control:
1. Consistent handpicking of the adults can help protect your plants from the ravages of this pest. A coffee can, about a third full of soapy water, can be used to collect the beetles.
2. There are several different insecticides that can be applied to the plant leaf surface to assist in controlling the adult Japanese beetle. Select only one product to apply at a given time. If a product does not work, witch to a different insecticide.
Product (Spray/Dust)Weight Active Ingredient Comments/Cautions
Weight Active Ingredient Comments/CautionsBayer Advanced 3 in 1 Insect, Disease & Mite Control 32 oz conc. Merit - Imidacloprid Low toxicity to birds, fish.
32 oz conc. Merit - Imidacloprid Low toxicity to birds, fish.Bayer Advanced 3 in 1 Insect, Disease & Mite Control 1.3 gal RTU
1.3 gal RTUBayer Advanced Rose & Flower Insect Killer 24 oz RTU
24 oz RTUOrtho Max Flower, Fruit, Vegetable Insect Killer1.3 gal RTU Acetamiprid Low toxicity to fish, bees.
1.3 gal RTU Acetamiprid Low toxicity to fish, bees.Bayer Advance Complete Insect Dust2 lbs Permethrin High toxicity to fish, bees.
2 lbs Permethrin High toxicity to fish, bees.Shultz Houseplant & Garden Insect Killer 12oz RTU Pyrethrin High toxicity to fish, bees.
12oz RTU Pyrethrin High toxicity to fish, bees.Ortho Max Home Defense Garden Insect Dust 2.5 lbs.Bifenthrin High toxicity to fish.
2.5 lbs.Bifenthrin High toxicity to fish.Ortho Max Home Defense Garden Insect Killer 24 oz RTU
24 oz RTUSevin Dust Bug Killer 1 lb. Carbaryl High toxicity to bees,
1 lb. Carbaryl High toxicity to bees,Sevin Ready-to-Use Bug Killer 32 oz. RTU earth worms. Moderately
32 oz. RTU earth worms. Moderately toxic to birds, fish. Do not use adjacent to water.3. Several traps have been developed to capture the adults. These trasp generally use a mixture of the aggregation and sex pheromones. Be sure to place traps at least 50 feet away from the plants you want to protect. Do not wait for the trap bags to completely fill before emptying. Poorly maintained traps can be a liability instead of a help. In spite of some evidence that they may draw in more beetles than would normally be present, some gardeners have repported positive results with the traps.
Predators:
Starlings...yes, those pesky starlings love to dine on Japanese beetles! Tachnid flies and tiphia wasps kill them. Native birds and chickens will feed on the larvae. You can help the birds along by turning the soil in autumn to expose the larva.
Repellent plants:
Catnip, chives, garlic, tansy and rue.
Resistant plants:
Box elder, Common lilac, Firs, Hemlocks, Hollies, Pines, Rhododendrons, Spruces, Scarlet oak, Tulip tree, White ash, White poplar and Yews.
