From The Ground Up: The Japanese beetle has arrived

The menacing Japanese beetles are finding our gardens again. If you are finding leaves that look like skeletons and three eighth inch metallic green and tan insects on your plants, the Japanese beetle has found your garden.

The Japanese beetle was first identified in New Jersey in 1916 after being accidently imported from Japan. They have slowly moved west since that first identification. It has only been in the last decade that it has become a pest in Eastern Iowa.

The life cycle of the beetle allows the beetle to be destructive to the gardener in two ways. The adult beetle emerges from the soil in late June or early July to feed, mate and lay eggs. The adult only lives for approximately sixty days but during this time it is in a feeding frenzy destroying the leaves on various plants. It does seem to have favorite foods such as grapes, roses, linden trees and fruit trees.

The remedies for the adult beetle are varied. The beetle is very slow moving in the morning so can be easily hand- picked or shaken off into soapy water. This of course is not practical for trees and large grape arbors. They can also be sprayed with Neem or pyrethrin products. These products should be used with caution and only according to directions so as not to be detrimental to bees and other pollinators.

The Japanese Beetle traps contain a pheromone lure that attract beetles from several thousand feet away. It has been proven that the trap attracts more beetles than it traps so if you are using the traps place them a far distance from the plants you are trying to protect.

After the adult has mated and laid eggs two to three inches below ground surface the eggs develop into grubs which feed on the roots of turf grass. This activity will result in large patches of brown grass which can be pulled up like a carpet. If you see this in your lawn, look under the brown grass to expose the grubs. Treat for grubs if there are more than ten grubs per square foot. If you have an infestation of adult beetles it does not mean that you have an infestation of grubs because the adult beetle can fly a very long distance to find their favorite meal.

If it is necessary to treat the grubs the treatment should be done by the end of August when the ground temperature is above sixty degrees. After the soil temperature drops to below sixty degrees the grubs move deeper into the soil and the insecticide won't reach them.

l For questions, call the Linn County Extension Master Gardener Hortline at (319) 447-0647.