Asiatic garden beetle

What is Asiatic garden beetle?

The Asiatic garden beetle is native to Japan and China, where it is not an important pest. It was first found in the U.S. in New Jersey in 1922 and has been a pest in the Northeast ever since. UF/IFAS notes it is usually less common and less damaging than the Japanese beetle, but it can build up enough to hurt turf, gardens and field crops.

Gardeners often meet it as a mystery: leaves on carrots, beets, peppers, herbs or flowers are shredded overnight, but nothing is there in daylight. The adults feed after dark and spend the day buried in loose soil or mulch at the base of plants. On summer nights they gather in large numbers on lit windows and screen doors.

The grubs feed on roots of grasses and weeds and can turn up in garden beds and lawns. UMass describes them as small but aggressive, and some of the preventive grub products that work on Japanese beetle grubs do not work on this species, according to Rutgers.

Plants it attacks: Lawn grasses and weeds (grubs eat the roots), carrot, beet and Swiss chard, parsnip, pepper, cabbage, turnip, lettuce, onion, corn, strawberry, Many herbs, fruits and ornamentals (UNH).

Signs and damage

• Leaves stripped, shredded or notched, especially along the edges, with no beetle in sight during the day.
• Damage that seems to appear overnight, because the beetles feed after dark.
• Lots of small brown beetles crawling on lit windows and screen doors on summer nights.
• Beetles found in loose soil near plant roots while weeding (UMass), or grub damage in poorly kept turf.

Asiatic garden beetle identification: what to look for

• Adult: About 3/8 inch (10 mm), plump and domed, dull chestnut to cinnamon brown with a velvety surface and a slight iridescent sheen.
• Larva: White C-shaped grub with a brown head and six legs, about 3/4 inch (19 mm) when grown. Raster has a curved row of spines across the underside of the last segment.
• Eggs: Laid in the soil in clusters of up to 20, held together by a jelly-like coating; they hatch in about two weeks.
• Timing: Adults emerge in late June and July and may keep feeding through summer. Grubs feed on roots in early spring.
• Damage: Ragged, notched leaf edges on vegetables, herbs and flowers from night feeding; root feeding by grubs in turf and garden soil.

Life cycle

One generation a year. Small grubs spend the winter in the soil and feed on grass and weed roots in early spring. They pupate in late May and June, and adults emerge in late June and July. Females lay eggs in the soil in clusters of up to 20, and eggs hatch in about two weeks (UNH Extension).

When to look: Check plants with a flashlight after dark from late June through summer. Look for grubs while weeding and digging in early spring.

Asiatic garden beetle look-alikes

A few things get mixed up with it:

• Japanese beetle (Popillia japonica): Adults are shiny green and copper, about twice as long, and feed in daylight. Grub has a V-shaped patch of spines.
• Oriental beetle (Anomala orientalis): Adults are blotched straw and black and feed very little. Grub has two parallel rows of spines.
• May/June beetles (Phyllophaga spp.): Also come to lights at night, but they are much bigger (1/2 to 1 inch) and darker reddish-brown, and they fly in late May and early June.

How to control Asiatic garden beetle

Cultural control

• Hand-pick beetles at night with a flashlight, or knock them into a wide bowl of soapy water (UNH).
• Use a light trap to catch adults at night (UNH).
• Cover herb and vegetable beds with spun-bonded row covers; UNH notes this helps less if grubs spent the winter in that same weedy soil.
• Clean up the garden in fall, and till under or compost weeds and plant debris (UNH).
• Avoid leaving weedy or fallow ground next to the garden, which can build up beetle numbers (UMass).
• Monitor adults with lights or light traps, or by sweeping the grass with an insect net at night (Cornell).

Biological control

• Rutgers says insect-parasitic nematodes work less well on Asiatic garden beetle grubs than on Japanese beetle grubs, and UMass notes scarab species differ in how much nematodes affect them.
• Milky spore will not help; it infects only Japanese beetle grubs.

Chemical control

UNH says grub control for this beetle is rarely needed in home lawns. For lawns that do need it, Rutgers notes imidacloprid, thiamethoxam and halofenozide do not work on Asiatic garden beetle grubs, and it uses a higher damage level for this species (15 to 20 grubs per square foot). For adults on vegetables, UMass says to check labels on broad-spectrum pyrethroid, carbamate and neonicotinoid foliar sprays, and names neem products and pyrethrin as organic options; it also notes that controlling grubs in vegetable beds may not be practical or needed. Follow any bee-protection directions on the label. Use only products labeled for this use; the label is the law.

Use only products labeled for this pest and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Keep lawns in good shape; UMass notes grub damage from this beetle is usually worst in poorly maintained turf.
• Keep weeds down in and around the garden, since grubs feed on weed roots.

When to call a pro

Call a licensed pesticide applicator (see our pesticide applicator license guide) if lawn sampling shows 15 or more grubs per square foot with dying turf, or if night feeding is destroying a large planting.

Related guides: Weed identification guide · All pests and diseases

Questions about Asiatic garden beetle

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