Tree doctor puts together the clues that reveal what's ailing the arbor

Dr. David L. Roberts is known as Michigan State University's Tree Doctor. But he could be the inspiration for the lead detective role in "CSI: Forest," if CBS would like to pick up a procedural on the exciting world of plant pathology.

The subject might not be for everyone. But the case that brought Roberts fame could be dramatized for TV: 

The timeframe, 2001-2002. Ash trees are dying mysterious deaths around Michigan. 

Low-angle shot: Roberts and an MSU entomologist are looking up at half-dead trees. He peels bark to find tracks in the wood, from some kind of worm. The entomologist points to D-shaped holes in the bark. "Clearly this is a chestnut borer infestation," the entomologist says.

"If they're chestnut borers," Roberts says, putting on aviator sunglasses, "then why have they developed a taste for ash?"

Roger Daltrey screams and The Who's "Won't Get Fooled Again" plays over opening sequence of Roberts hiking in old-growth forests, examining herbicide containers, looking concerned over mulch piled up too high around a homeowner's maple.

Little green bugs

In the real world, there's more persistent toil than made-for-TV drama in Roberts' work. But it was pretty dramatic the day his ash investigation caused little green bugs to infest his lab.

Roberts discovered that the mysterious die-off of ash trees in Detroit suburbs in 2001-2002 was not caused by ash yellows disease or the native chestnut borer -- two theories at the time -- but by the invasive emerald ash borer, the Asian bug that has since wiped-out most of Michigan's ash and has spread as far as Colorado, Texas, and Quebec.

He became concerned in 2001 when investigating a condominium's complaint that all 80 of their mature ash were dying. Then, suburban Detroit communities were using up budgets to cut down dead ash. "They wanted answers."

Roberts drummed up grants to conduct DNA tests on ash around the area to see if disease was the problem. In short: It wasn't.

He collected worms from dying trees. MSU entomologists told Roberts the larvae were from the two-lined chestnut borer, a dark brown insect native to Michigan. They sometimes bored into non-chestnut trees. But it was "weird" that they would be infecting so many ash trees, Roberts says.

The only way to know for sure was to see what the larvae became. So he took samples of sick ash to his lab, sealed them in plastic bags, and waited. The fierce bugs "could actually chew their way through the plastic bag to get out." 

The vivid green insects "were flying around my lab and everything." Roberts had oak and maple samples in his lab, but "they would always fly back to the ash logs because that's what they recognized."

Farm boy to tree doctor

These days, especially in the spring as trees come out of winter dormancy, Roberts is busy with calls and emails from around Michigan and the country. 

He laughs when people tell him he's got a reputation for solving any dead or dying tree mystery. There are others who have his knowledge, Roberts says. "I don't know how many are as diverse as I am, because of my diagnostic clinic background.... I'm a pretty broad generalist."

Roberts grew up on a self-sufficient farm in central Ohio, raising chickens, pigs, dairy cows, and crops.

He went into ag studies at Ohio State. He was also a generalist in college, too much of one. "I got a letter from the dean saying you've got to declare a major sometime here, before it goes on much longer. I figured that horticulture and agronomy were just too easy, so I chose the most difficult subject that I could find, which is plant pathology," or, what makes plants sick.

He eventually earned his PhD at MSU, became the director of the university's plant and pest diagnostic clinic (1984-1998), and worked at investigating sick plants from pines to soybeans to houseplants. He then took the role he holds today, a senior academic specialist focusing on arboriculture.

While professional arborists charge for diagnostics, Roberts is generous with his services. 

"That would be pitch mass borer, an insect," he says when this writer describes the sick spruce in his yard, dropping needles and covered with gooey, sappy lumps. "You can actually dig into it, take the pitch off, and you can find the larvae in there... get a knife or something and just dig in there. It's awful messy, you'll get resin all over...." 

Though he has to raise grants and find other funding to cover his costs, it's part of his duties to travel around the state to investigate arboreal problems. "I try to get around as much as possible. There's very few people that I turn down."

Roberts can diagnose what ails a tree, but some problems have no cure, yet.

Like the ash borer. There've been efforts to introduce the EAB's natural Asian enemies, such as wasps that kill the larvae, but Roberts isn't "real excited" about using other foreign bugs as a solution.

He thinks the issue is that Asian ash trees are genetically resistant to the EAB, and North American ash are not. MSU planted both native and Asian ash at its Tollgate Farm in Novi. "The emerald ash borer didn't even attack those (Asian) trees, much." 

Roberts doesn't know how to fix the problem of invasives. "I don't think anybody does, except maybe limit our intercontinental trade." 

The biggest danger to Michigan trees

What are Michigan trees' biggest danger -- native pests and disease, invasives, or humans?
"You want me to select one of those?" 

Roberts continues, "The invasives are definitely the biggest problem, but the humans as well -- after all, we've transported the invasives here, so that combination is both deadly to our native forests and urban forest." 

The urban forest: It's not easy to picture a tree surrounded by parking lot pavement, or that sugar maple in your yard, as a forest. But that's what it is, and humans are its biggest threat, Roberts says. "The urban forest, where some of the major (problems) are pesticides, over-care -- too much water and so forth."  

People assume that a tree is a mighty, strong plant. Nothing can kill it -- certainly not an innocent mistake by a homeowner. But Roberts has seen otherwise. Chemicals, bad arborists, pruning at the wrong time of year -- he's seen it all. (See sidebar.)

His basic advice to homeowners is, treat your trees "as nature would. If we tend to water them or fertilize them, do things around them such as grow dense turf under them, we're essentially violating nature's laws, or God's laws, whatever your leaning is. Trees are designed to live in forests with other trees." 

"Because they have been there so long, people take them for granted. They put most of their landscape finances into lawns... They figure this big tree is always going to be here, and they never have to do anything for it." 

Mark Wedel is a Kalamazoo-based freelance journalist who’s covered a bewildering variety of topics since 1992. Before that, he worked with plenty of trees on his family’s nursery farm.
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