Spring & Summer Insects – Japanese Beetle

Remember digging around as a kid and coming upon these white grubby worms. We used to try to fish with them. Don’t remember if I ever caught anything. Then there were these shiny, metallic green insects with copper-brown wing about 3/8-inch in length. These insects are probably both different stages of the Japanese beetle, and this guy can reek havoc on your lawn and garden!


The beetle starts as a small white egg laid in the soil. If moisture is sufficient, they will absorb it and enlarge, becoming rounder as they do. They grow into the white grub stage that is so familiar in lawns. By August they are about full size (almost an inch long). They can live in almost any soil and a major infestation of these grubs can destroy a lawn in short order.


Japanese beetles overwinter in the grub stage. As the soil temperature lowers they move deeper. When the temperature starts to rise again in the spring they move back up to the roots of you plants and start feeding again. After a feeding period of 4-6 weeks, the grubs pupate in an earthen cell and remain there until emerging as adults. Adults generally emerge from the ground sometime from May to July, depending on your location. They live for about 30 – 50 days feeding on your plants. After a few weeks the females dig into the soil and lay their eggs. They can lay 40 – 60 eggs in their lifetime.


Adults fly long distances to food plants; so, just because you see an adult infestations, does not necessarily mean that they are in your turf. Adults feed on leaves and flowers of many plants including rose, bean, grape, and crabapple. Feeding injuries to leaves usually result in conspicuous “skeletonizing injuries” where larger veins are avoided leaving a lacy “skeleton” of the leaf.


Turf control. Look for areas of brown turf and search in adjacent green areas for grubs and pupae. If the damage is extensive insecticides may be needed to control grubs and adults. There are several granular insecticides for grubs. The best time to apply is from mid-July until end of September. There are also several organic treatments as well.


For adult beetles simply removing the beetles by hand may be the best solution if the infestation is not severe. The presence of beetles on a plant attracts more beetles. Thus, by not allowing beetles to accumulate, plants will be less attractive to other beetles. Different chemicals are available to kill the adults but should never be applied in windy conditions or when bees are foraging.


Japanese beetle traps. Think twice before using the trap. Most traps contain a lure with the scent of flowers and the sex pheromone of the female. The pheromone will attract beetles from a few thousand feet resulting in more beetles fling toward traps than are caught.


Cultural Control. Carefully selecting plants that are not susceptible to Japanese beetles is the best way to prevent them. Certain common landscape plants are inevitably attacked. Your local nursery should be able to provide you with a list of plants seldom damaged as well as offering suggestions on best chemical applications for your area to use to control a Japanese beetle infestation.

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