Japanese beetle has staying power

The last word on Japanese beetles is that they are here to stay, at least as long as someone in the neighborhood is intent on a wide expanse of turf rolling from front door to curb. All the gardener can do is make adjustments, in attitude and practice.

In his essay, “The Idea of a Garden,” Michael Pollan reminds us that while gardeners have a “legitimate quarrel with nature – with her weeds and storms and plagues, her rot and death,” we best not take it too far. Consider our infatuation with DDT’s victory over insects. “Better to keep the quarrel going,” he writes, “than to reach for outright victory, which is dangerous in the attempt and probably impossible anyway.”

And so I will continue to hand pick the beetles in their season, thankful that the absence of any turf in Marjorie’s garden keeps their numbers low. And I will continue to see poetic justice in the beetle’s appetite for Norway maple – one more reason to banish this weedy tree from our gardens and streets.

Perhaps the smartest adjustment in garden practice is shunning those plants that we know attract Japanese beetles. American and European lindens, once popular street and lawn trees, look scorched by midsummer, every leaf skeletonized by hordes of the beetle. I recall such a scene from my days in Orono, a long row of evenly spaced defeated lindens lining the perimeter road of campus, and wonder if this was a strategy to keep the beetle on the fringes.

Japanese beetles seem to favor species in the rose family. In addition to garden roses, they seek out the leaves of plums, apricots and cherries, mountain ash, and apples, including some crabapples. But sometimes there is no explaining the choices they make. I have watched them devour the leaves of Sargent cherries while leaving nearby crabapples untouched.

Among the many varieties of crabapples, some are considered more resistant to the beetle than others, at least by some observers. Varieties reported to be highly to moderately resistant include Brandywine, Indian Summer, Profusion, Red Jewel, Sargent, Snowdrift, and White Cascade.

My favorite crabapple, Donald Wyman, turns out to be on at least one list of least resistant, but that will not stop me from growing it in my own garden and recommending it to others. I had one in my Orono garden and only occasionally found the beetles feeding on it – probably because they were congregating on the nearby Virginia creeper. And the splendid specimen in Littlefield Garden on the Orono campus went undamaged in the seven years I was there.

Other trees to avoid include horse chestnut, black walnut, and – not a surprise – Japanese maple. Unfortunately the birches, including our native species, must be added to this list.

So what can we plant? Tree species that are resistant to adult Japanese beetle feeding include pagoda dogwood (Cornus alternifolia), red maple (Acer rubrum), red oak (Quercus rubra), and white ash (Fraxinus americana). Among shrubs, lilacs, forsythia, and hollies all seem to be resistant to varying degrees. In my own experience, I have grown chokeberries (Aronia sp.), fringe tree (Chionanthus virginiana), spireas (Spiraea sp.), and ninebark (Physocarpus opulifolius), all beetle-free within a few feet of the devoured Virginia creeper.

It is beyond the scope of this column to list every resistant variety of garden plant. The Internet is filled with such lists, as are the past histories of local gardens. Check around.

Keep in mind that resistance is not the same as immunity. I am of the opinion that a hungry Japanese beetle will eat almost anything.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to reesermanley@ptc-me.net. Include name, address and telephone number.