Martha Maletta, Home Horticultural Consultant
Dated - July 09, 2004

The periodical cicadas are gone, and the Japanese beetles have arrived in considerable abundance if calls to the Rutgers Master Gardener Helpline of Hunterdon County are an indicator. Unlike the 17-year cicadas, Japanese beetles are an annual “event”, some years seemingly worse than others.

Insect populations will fluctuate year to year for many reasons. One possible reason there may be more Japanese beetle adults this year, if that is, in fact, the case, is the adequate moisture last July and August during egg laying and hatching. Soil moisture aids survival.

The Japanese beetle is, in effect, two quite different pests in one. The larval stage, the grub, is a pest of lawns. The adult beetle is a pest of a wide variety of plants: trees, shrubs, flowers, fruit. Control of each stage requires different tactics that, in terms of reducing pest potential, are unrelated: controlling the grubs will not protect plants from the adults, and controlling adults will not protect lawns from grubs. The reason: the adults are very mobile and readily fly 1 to 2 miles. So, eliminating grubs from an infested lawn in late summer or early fall will not prevent damage from adults in the following year. And using insecticides to kill adults and protect plants during summer will not prevent a grub problem.

Grub control materials are best applied when a survey of the lawn in August shows that there are grubs present in numbers that would result in significant damage. There are some insecticides that have been developed which can be applied early in the summer before egg laying. However, this means that they might be applied before a grub survey can be done; the application may not have been needed. For complete information on white grub control in turf, send a SASE to RCE Hunterdon County, P.O. Box 2900, Flemington, 08822 or visit the RCE website at for the Fact Sheet “White Grubs”.

Controlling Japanese beetle adults is another matter. They can be difficult to manage because, while insecticides may reduce numbers temporarily, new individuals will probably arrive shortly. This can make beetle control a frustrating task. Hand picking for a light infestation is an option. One tactic NOT to use is beetle traps, which may lure more beetles to the area than there would have been without the trap. Contact the Rutgers Master Gardener Helpline, 908-788-1735, M-Th 9 to 12 and Th 12:30 to 3:30 for insecticide recommendations for certain ornamental plants.

Like the cicadas, the Japanese beetle adults will gradually disappear after a few weeks, but unlike the periodical cicadas, they are sure to be back next year.


The Melda C. Snyder Teaching Garden at the Rutgers Snyder Research and Extension Farm is the site of two upcoming Friday morning programs. July 16th the topic will be Fall Vegetable Gardening. It’s just about time to plan and plant for harvests until frost and beyond. On August 6, Dr John Grande, Farm Director and turf expert, will discuss and demonstrate Renovating Your Lawn. Please RSVP to 908-526-6293 if you plan to attend either or both of these programs and for directions to the farm.

The 5th Annual Garden Party in Colonial Park Gardens will be held July 17th, 1 to 5 p.m. It will feature lectures and workshops, music and refreshments, plants and plant experts to answer questions. Call 732-873-2459, ex. 22, for more details.