Beat Japanese beetles with a one-two punch

I remember the year when Japanese beetles found my garden in Orono. I had planted a Virginia creeper at the base of the front steps and by the second year this vigorous vine had reached the porch railing, heading up the corner post. Then one day in late June they arrived, half-inch-long beetles, metallic green with copper-brown wing covers. Small white tufts project from the sides and rear of the wing covers, a feature that helps distinguish them as the enemy.

In one day, a half-dozen beetles skeletonized all of the vine’s upper leaves. This is their way, top down. And so the battle began. For three weeks, I waged war in the early morning and late evening, before and after work, brushing beetles off the leaves into a pail of soapy water. I left the drowning beetles on the porch during the day, sending a message to the next wave of invaders: this is your fate.

They were not deterred. What began as a five-minute chore on either end of the day became an impossible task. I could not keep up as reinforcements arrived, spreading to other plants in the garden. At the end of each day, there were hundreds of beetles in the pail.

Yet while there were always beetles around – some would miss the pail and drop to the ground, only to return to feeding the moment I turned my back, while others flew in from miles away, attracted by the scent of the feeding frenzy – the damage to my plants was minimal, and gradually I prevailed. One morning, three weeks after they arrived, the beetles were gone.

The adults were gone, but not before ensuring the start of next year’s invasion. While they fed on my garden plants, each female (typically larger than the male) had stopped long enough to burrow three inches into the nearby turf and lay a few eggs, doing this several times until about 50 eggs had been laid. The eggs would hatch by midsummer and the grubs would spend the rest of summer feeding on the grass roots.

After spending winter deep in the soil, the grubs resume feeding in early spring, then pupate for a short time before becoming adults and emerging to feed in the garden again.

Since this insect spends about 10 months of the year in the ground, we need to combine mechanical control in the garden with a nonchemical control of grubs in turf.

I recommend insect-eating nematodes – microscopic parasitic roundworms – that actively seek out grubs in the soil.

These nematodes have a symbiotic relationship with a single species of bacteria. Upon penetrating a grub, the nematode inoculates the grub with the bacteria. The bacteria reproduce quickly, feeding on the grub tissue. The nematode then feeds on this bacteria and progresses through its own life cycle, reproducing and ultimately killing the grub.

Nematodes may be purchased in lawn and garden shops or through biological mail-order catalogs – such as The Green Spot, www.shopgreenmethods.

com, (603) 942-8925). Typically sold on a carrier, they can survive for a month or two under cool conditions, but are best used as soon after purchase as possible. They are applied with any standard insecticide applicator. Once mixed with water, nematodes must be applied quickly, as they have a high oxygen requirement. Follow accompanying directions carefully for best results.

And so there you have it, a double-edged sword to wield in the battle against the Japanese beetle, a combined strategy of handpicking and biological control. This approach has proven to be very effective, especially when entire communities work together to eliminate the beetle from turf areas.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to reesermanley

@shead.org. Include name, address and telephone number.