The Japanese beetle and Japanese beetle grubs are a notorious landscape pest found in the eastern United States. Japanese beetles are voracious feeders in landscapes and gardens, with over 300 species of plants (turf, flowers, fruits, shrubs, trees) the beetles regularly dine on. Roses, lindens, small maple trees, fruit trees, and Virginia creeper vine are most often targeted by the beetles.
The beetle was first discovered in Denver back in 2006. Since then, the beetle infestation is now firmly entrenched and spreading rapidly.
Life Cycle and Plant Damage of the Japanese Beetle Grubs
Japanese beetles spend most of their lives as a soil grub. Grubs are up to 1 inch long, C-shaped, and have six legs. In the spring as the soil warms, Japanese beetle grubs migrate to the surface briefly feeding on grass roots. In late June and early July, adult beetles emerge. Shiny metallic green, one-half inch long beetles swarm plant foliage – feeding on the top of the leaves. Beetles quickly skeletonize the foliage by chewing in between leaf veins leaving a lacy appearance. Leaves turn brown and prematurely fall off. Adult beetles are most numerous in July, but may persist well into August.
The adult female beetle burrows into the soil laying up to 60 eggs. In late summer the eggs hatch into grubs. The grubs resume feeding on turf roots and this is when injury occurs on your lawn. With roots eaten and the onset of hot dry summer months, grass quickly fades and turns brown. Small dead patches quickly coalesce into large areas of dead grass.
How to control Japanese beetle
Soil injections are available for American elm, birch, linden, maple, and roses. Soil injections offer longer lasting control.
Infested plants may also be sprayed. Two applications may be necessary. Currently, no applications are available for fruit bearing plants. Contact a Denver pest control expert for suggestions on how to control Japanese beetle on your property.
One application of granular slow release insecticide will provide yearlong control of Japanese beetle grubs in the lawn. The application should be made in June just prior to egg laying. Once the damage is evident, complete control of grubs is not possible and the damage will continue.
The key to Japanese beetle control is preventative applications. Once beetles appear on plant foliage or damage occurs on your lawn, control is difficult.