Leaf leaks have experts treed

Bug expert says it's bugs, tree guy says it's trees ...

October 19, 2006|By Jill Rosen | Jill Rosen,SUN REPORTER

Something is making Baltimore-area trees let loose so much moisture that people, thinking the skies have opened, are reaching for umbrellas and running for cover.

What in the name of Arbor Day is the deal?

Not an actual weather disturbance or copious amounts of

morning dew. The water mains are fine and air-conditioners blameless. A coming apocalypse seems about as likely as extra-terrestrials or sad tree tears.

Dozens of such hypotheses - more creative than credible - have surfaced to explain the weeping tree phenomenon, where typically unassuming maples and poplars drop buckets of mysterious liquid, so much that it's being mistaken for a misty rain.

But Maryland's scientific elite - speaking with nothing close to unanimity - have found two premises to half-heartedly endorse: One is pretty gross, the other pretty obscure. The fiercest advocates of each faced off this week in Patterson Park, hoping to solve the whodunit.

Maryland entomologist Mike Raupp, banking that bugs are behind everything, waits near the Pagoda, a long-handled tree clipper in one hand, a plastic bag of leafy evidence in the other.

Hugo Lam, director of Baltimore's parks conservation program, drives in from his Druid Hill Park office empty-handed but with confidence to spare. He has no doubt that something called "guttation," a natural yet unusual type of plant secretion, is at work.

They shake hands and slosh off into a driving rain - real rain this time - for an hourlong session of leaf-picking, limb poking and way-wonky sleuthing.

When he heard trees were releasing odd fluid, Raupp, a University of Maryland professor, immediately thought of minute insects known for settling onto conifers, bingeing on nutrient-rich sap, then purging the excess into the air. The sticky-sweet excretion is commonly called "honeydew."

Aphids could be the culprit, but Raupp thought scale insects were likelier suspects. Members of the coccidae family, these sneaky characters look more like bumps on branches than bugs. They favor urban environments and suck and spew sap with gusto, but unlike aphids they'll settle on any type of tree.

To prove his case, Raupp trolled the park in search of tell-tale lumpy branches, curled foliage and the sooty mold honeydew provokes.

"Bugs are easy," he says. "They always leave something behind."

Lam, meanwhile, a recent graduate of Yale's School of Forestry, can't get over how anyone - let alone scientists - can deduce anything but guttation from the evidence.

"What are these people thinking?" he says. "Just open any biology textbook. It's common knowledge - or at least I thought it was."

Because guttation's trademark dripping leaves are usually spotted on herbaceous plants, particularly strawberries, Lam agrees it would take some doing for trees to get in on the act.

That said, he thinks that the saturated soil, the humidity and the recent temperature swings could shock trees into the behavior.

"The way I look at it," Lam tells Raupp, "[the trees] are just confused right now."

The two, shelving their differences in the name of science, ignore the driving rain and prowl the park for clues.

Raupp quickly spies a tiny nub on a thin limb, a bump that to untrained eyes would look as if it's supposed to be there. But Raupp knows it's a bug's doing - an egg sac holding what will someday launch hundreds of microscopic insects.

Yet despite this and many egg-laden branches like it, Raupp eventually declares with a sigh, "There's no smoking gun here."

"I've got to be honest," he adds. "I haven't seen enough in Patterson Park to think that bugs were triggering what [we're] talking about."

Not ready to give up, the two head toward Butcher's Hill, a sort of ground zero for weeping trees, which neighbors have spotted along Lombard, Chester and Baltimore streets.

While Raupp uses his long-reach clippers to grab leaves from a Lombard maple, Kirsten Lapointe comes outside to see what the men are up to.

Her eyes widen when she finds out they're investigating the leaf leaking. She interrupts Lam's Guttation 101 to mention that an "older lady" who lives on the block recently told a group of youngsters to stop freaking out, because the trees have been doing this for years.

"See?" says Lam, almost giddy at the prospect of being proven right. If it has happened before, a natural explanation like guttation might make more sense. "We must listen to our elderly!"

It's about this time that Raupp gives it up.

"Guttation makes me happy," he says flatly. "I could live with guttation."

Not that other tree experts are.

"I just don't see it," says Gary Coleman, a University of Maryland tree biologist. "I've been working with trees for a long time, and I wouldn't go to Las Vegas and wager on that."

Joe Sullivan, a forest ecologist in Sullivan's department, is equally skeptical.

Even a believer like Steve Britz, a plant physiologist with the U.S. Department of Agriculture in Beltsville - someone who swears his strawberries were guttating just the other day - isn't 100 percent sold.

"I'm, um, probably like 75 percent sure," he says. "Certainly more than 50 percent."

Not the most ringing of endorsements.

When it comes to the weeping trees, Mike Galvin, an arborist with Maryland's Department of Natural Resources, isn't sure of much. Not about bugs. Not at all about guttation. Just that the whole thing is "freakish."

His best arboreal advice? Get an intern on it.

"There's got to be something else at play here," he says. "We need to get some grad student to get a grant and check it out."

jill.rosen@baltsun.com

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