Tiny killer destroys work of years at Ladew gardens Topiary hemlocks fall prey to pest

October 04, 1993|By Mike Klingaman | Mike Klingaman,Staff Writer

On crisp autumn mornings, Lena Caron strolls the terraced grounds at Ladew Topiary Gardens to watch the mist rise through soft green windows carved of living hemlock.

It is, she says, "the most beautiful thing I've ever seen."

But a tiny invader threatens to turn that scene to mulch.

"See this?" says Mrs. Caron, Ladew's director, plucking a yellowed bough from the hemlock windowsill. "This is what we're fighting."

The foe, an insect from Japan called the hemlock woolly adelgid, attacks with a one-two punch that is half vampire, half viper: The bug sucks the tree's sap while injecting lethal spittle.

It's a killing combination: Infected trees generally die within four years.

The woolly adelgid arrived in the United States decades ago and spread very slowly at first. Riding the wind from place to place, it found Eastern hemlocks to its liking, but not the species of tree found in Western states.

Though small -- four insects can fit on a pinhead -- the adelgid already has felled thousands of acres of hemlocks in forests from Maine to the Carolinas.

More than three-quarters of the graceful, soft-needled trees are dead or dying in Virginia's Shenandoah National Park. The insect also has invaded Catoctin Mountain Park, near Camp David, assaulting hemlocks that shade presidential trout streams. Ecologists fear the trees' demise will lead to warmer streams that will drive away the fish.

No less vulnerable are the trees at Ladew in Monkton, one of the United States' most popular topiary gardens. Eighty percent of Ladew's topiary is hemlock.

Some of those trees already are on death row.

Next month, when the Harford County attraction closes to the public for winter, workers will rip out twin arcs of dying hemlocks, each the length of a football field.

The 60-year-old trees, the first planted in the 22-acre garden, will be ground into mulch for Ladew's flower beds -- an ignominious end for the once-proud hemlocks.

L "I think I'll hide under the bed that day," says Mrs. Caron.

Those 15-foot-high hemlocks will be replaced with healthy 2-foot yew shrubs and a latticed green trellis. The cost of the project is expected to top $40,000.

Meanwhile, Ladew has launched an aggressive campaign against the woolly adelgid in an effort to slow the demise of the remaining hemlocks.

The trees are drenched in horticultural oil, suffocating many of the aphid-like insects. Then the hemlocks are pumped full of nutrients -- sea kelp and iron.

Ultimately, however, the trees will succumb. For that reason, all the hemlocks eventually will be removed from the gardens, which were created by the late Harvey S. Ladew, a local sportsman, and are maintained by a nonprofit foundation bearing his name.

Mr. Ladew was intrigued by the art of topiary -- the trimming of ornamental shrubs and trees into fantastic shapes -- and cut his plants to resemble animals, birds and other objects.

But the constant shearing needed to maintain those shapes takes a toll on some species, particularly hemlocks, lowering the trees' resistance to pests and diseases.

"Hemlocks don't always take well to topiary; pruning them is like shooting yourself in the foot," says Barbara Paca, the landscape architect hired to oversee Ladew's hemlock replacement. "For these trees to have survived 60 years reflects well on the staff. I'd have figured 40 years, tops."

Certain sections of the garden are dying faster than others. Already, visitors are beginning to step through raggedy windows of sculpted hemlock, confusing those openings for doorways.

"Losing these trees is a terrible shock, but we've got to face reality," says Barbara "Bunny" Hathaway, head of Ladew's garden committee. "You can't have scruffy stuff in a tourist garden."

More than 25,000 people from 40 countries visited last year.

Unaffected by the ravaging pest are some of Ladew's most striking topiary figures, including a Chinese junk made of privet, and a buddha and a swan hedge shaped from yew.

Ladew officials discovered the woolly adelgid four years ago, wrapped in tiny white balls and woven like tinsel around needles and branches. Each "snowball" contains adult insects and up to 300 eggs.

Initially, says Mrs. Caron, visitors liked the snow.

"It's so cute," she recalled one saying.

"My hemlock at home has the same thing," she quoted another. "I cut the branches and use them to decorate the house."

Then came the sad truth: The woolly adelgid is a wolf in sheep's clothing.

"It's insidious that this insect looks so pretty," says Mrs. Caron.

Worse, the invader plays by its own rules, defying normal insect behavior. It is most active during winter rather than summer; and the adelgid survives some conventional pest-control strategies.

For example, the accepted practice of pumping stricken trees full of high-nitrogen fertilizer, to stimulate new growth, actually triggers a baby boom among the bugs: The more new tree there is to feed on, the faster they reproduce.

"Giving nitrogen to infested hemlocks is like throwing gasoline on a fire," says Ms. Paca. "The adelgid population just explodes."

Ladew's plight gives Baltimore-area homeowners some advance warning, she says.

They should check their hemlocks for snowlike infestations and use this treatment: Spray with horticultural oil, sold in garden centers, in early fall -- or whenever egg sacs are spotted.

The oil should be applied to the entire tree, because the insects often hide underneath branches.

Scientists seeking a biological weapon against the pest pin their hopes on a tiny blind mite, also from Japan, that attacks the adelgid's egg colonies.

Though research with the mite is promising, a cure is years away -- too late to save Ladew's hemlocks.

"We have pictures of the trees when they were tiny," says Mrs. Caron. "I'll be so upset when they're gone. But you go on; you find another spot of beauty.

"After all, it is a living garden."

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