I have seen several articles coming out saying that Japanese beetle populations are on the rise in Missouri. The Japanese beetle has been in Missouri for over 20 years and has been showing itself in great numbers for the last 4 to 5 years in southeast Missouri.
The adult Japanese beetle is about ? inch round, with a green and orange or copper metallic back and black sides with white spots of small hairs. These adults usually emerge by June and continue to feed for as many as 8 weeks. The larvae is a grub, overwintering deeper in the soil and coming to the surface to reproduce.
It has a veracious appetite for vegetation and does not differentiate between herbaceous ornamentals, fruit, vegetables or trees. Some of its favorite plants include roses, crape myrtles, elm, lindens, grapes, sassafras, Japanese maple, peach, cherry, plum and crabapple. These are just a few of the popular choices in our location.
From afar damage may appear as a yellowish or brown coloration to a bush or tree. As you move closer you will see the leaves have been skeletonized as the beetle eats all but the veins. Plants can recover from this but the longer they go without leaf tissue the less they will produce energy for the plant.
As the population has moved through the U.S. they have hit high concentrations which will last for about 5 years and then the population seems to level out likely due to natural predation. Hand control may be obtained by placing a bucket of soapy water beneath a shrub or small tree and shaking the branches so the beetles fall in. This can be affective if the insects are caught soon enough. As Japanese beetles move into your landscape they will attract more beetles. Plants can also be covered with a fine cloth to prevent flying beetles from accessing the leaves.
There are Japanese beetle traps which will fill with adult beetles and can then be emptied into soapy water or in a sack and burned however the danger of using these traps is that they will attract more adults to the yard where they are hung.
Chemical control measures may be applied as a contact to the adult beetle but scouting should be continued in June and July and control should be reapplied as necessary based on the label recommendation. Once a control has been applied to the first population, a second and third population may enter the area re-infesting the same plants. Control can also be hard to achieve if neighbors are not working toward the same goal.
Permethrin's, bifenthrin and pyrethroid's are effective in controlling adult beetles as can be carbaryl. Applications should be precise to the beetles and consideration should be taken for the health of bees in your landscape when you are deciding on a method of control. You may do just as well by spraying insecticidal soaps on shrubs that are heavily infested. Granular applications of 'Merit' may be used on turf to control the larvae stage of the Japanese beetle.
The larva of the Japanese beetle is a grub that hatches later in the summer, July and August, increasing in size within 40 days before moving deeper to overwinter. Feeding is concentrated on the roots of turf grasses, usually those that are irrigated. If populations are high enough, this feeding can cause damage to the health of turf.
Source: Japanese Beetles in the Urban Landscape. M.F. Potter, D.A. Potter and L.H. Townsend. University of Kentucky Cooperative Extension Service. Entfact-451.
The Extension office is open Monday - Friday, located in Kennett, Missouri at 233 North Main Street. For horticulture questions contact the horticulture specialist at 573-686-8064. MU is an equal opportunity/ADA institution.