The plant doctor is in
For nearly two decades, an emeritus professor has treated ailing flora at a monthly Botanical Garden clinic

By D. Lyn Hunter, Public Affairs



With a “potside” manner any physician would envy, Professor Emeritus Robert Raabe and a cadre of colleagues diagnose all the ailments that foliage is heir to.
Noah Berger photo

25 September 2002 |

The Sick Plant Clinic is held on the first
Saturday of every month, from 9 a.m. to noon, at the Botanical Garden, 200 Centennial Dr. The next session is scheduled for Saturday, Oct. 5. For information, call 643-2755.

Though he doesn’t look much like a doctor — dressed in faded flannel shirt, suspenders, and dirt-stained khakis — Robert Raabe is one of the first experts some worried people turn to if a loved one isn’t doing well.

Even before his “office” opens, the patients are lined up, waiting for Raabe to carefully look them over. The maladies he sees — viruses, powdery mildew, rust, black spot, insect infestation — are not usually fatal but can riddle the afflicted with unsightly cankers, carbuncles, and pockmarks.

The professor emeritus of environmental science, policy, and management treats plants, not people — although the distinction can be lost on some avid gardeners, for whom a prized pelargonium is as deserving of care as any other family member.

Those who dote on their lavender, lobelia, or lupine can bring their charges to the Botanical Garden’s free “Sick Plant Clinic,” held on the first Saturday of every month. There Raabe — along with Nicholas Mills, a Berkeley professor of insect biology, and a cadre of other experts — will inspect plants, diagnose their problems, and offer up possible solutions.

“Some folks come in very worried,” says Raabe, who’s conducted the clinic for nearly 20 years. “But the most common ailments — fungus or insects — won’t kill your plant, they’ll just make them look weird.”

His prescriptions for controlling disease are almost always biologically based and chemical-free. For example, Raabe sometimes suggests Neem Oil, derived from a tree in India, to control fungi. “It’s available at most nurseries,” he says. “It smells funny, but can be effective.”

Another natural method for limiting certain fungi, such as powdery mildew on roses, is to spray the affected plant with water at noon. The spores are released at around that time every 24 hours.

“This kills the spores and prevents them from causing new infections,” Raabe explains. “It’s also important to do it at this time of day so the leaves can dry quickly. If they stay wet for too long, then there’s a risk of getting rust or black spot.”

The Bay Area’s unique climate — dry summers, cool nights, and foggy skies — is ideal for the production of some disfiguring fungi. And the area’s heavy clay soils are a prime breeding ground for another insidious disease: root rot.

“People like to grow non-native plants that aren’t compatible with our soil,” Raabe says. “This is usually done for aesthetic reasons, but it can be harmful to the plant.” Raabe recommends that people learn about the origins of their non-native plants and try to replicate the conditions in which they naturally thrive.

Another common mistake gardeners make, he says, is putting plants with different requirements next to each other, such as a sun-loving, drought-resistant sage adjacent to a thirsty fern that prefers shade.

Raabe employs his avuncular “potside” manner to educate gardeners about the various things that can affect their plants. He also encourages them to learn to co-exist with diseases, because the persistent and hearty organisms that cause them “aren’t going away anytime soon.”

Every now and then, the clinic’s experts see a disease they can’t diagnose. That’s when the real detective work begins, often starting with questions about where in the garden the afflicted plant is located. Sometimes it’s necessary to take such plants into the lab before a cause can be determined.

“In some instances,” says Raabe, “the plants are damaged because they’ve come into contact with toxins, due to leaks in gas or sewer lines, or even cracks in swimming pools.“

While most visitors simply want one or two problem plants looked at, there are a handful of clinic “groupies” who come just to hang out and listen to the diagnostic discussions. One regular, says Raabe, is recording the sessions with the hope of writing a book about what she’s learned there.

During summer months, up to 30 people come to each clinic. That figure dwindles significantly in the winter; but, says Raabe, there has never been a day when no one showed up.

“We always have a good time,” he says of the clinic’s informative but relaxed atmosphere. “We laugh quite a bit and try not to get too serious.”

Hopefully, they can convince fretful home gardeners to do the same.


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