Title: Chemical-free weed control at San Francisco Botanical Garden
[Pesticide Research Institute 04 Feb 2014] — Over the past fifteen years, the San Francisco Botanical Garden (SFBG) in Golden Gate Park has become a true model for chemical free weed management under the guidance of Bob Fiorello, a dedicated horticulturist and IPM professional. Using predominately non-chemical methods, Bob and his staff of eleven gardeners care for 55 acres of diverse plant communities representing over 8,000 different species from around the world. “When it comes to parks and pests, most of what we do is weed management” Bob explains while pointing out a new addition to the garden, a hillside featuring Mediterranean drought-resistant grasses and shrubs. “This area used to be all blackberries and ivy. We cut back the vegetation, used heavy machinery to clear it, and brought in new soil… volunteers helped dig out the blackberry roots the backhoe couldn’t reach. After two years the plants are settling in, and sheet mulching keeps the weeds down. If we had relied on herbicides to clear the hillside it would have taken multiple treatments and a considerable amount of product to achieve similar results…if we were lucky.” Using chemicals isn’t always a quick fix for a weed problem. “When we used to apply Roundup® it could take 2-3 weeks to work because of our cool, foggy climate. Often a new crop of weeds would grow up while we waited for the ones we sprayed to die.” The Botanical Garden’s adoption and commitment to chem-free practices resulted from concern over the health impacts of pesticide exposure and the need for better pest management solutions. Comment
As a San Francisco Recreation and Park facility, SFBG adheres to the policies set forth by the city’s landmark IPM ordinance, also known as Chapter 3 of the San Francisco Environment Code. The ordinance was enacted in 1996 and has inspired and helped guide communities around the world to establish their own IPM programs. Bob had a hand in writing this legislation and developed the Park Department’s formal IPM policy at that time. At the botanical garden he now enjoys the challenge of putting theory into practice. “After all this time, this stuff is still a lot of fun!”
For the Garden staff, an IPM “best practice” is defined as the most efficient and effective way of managing a pest safely and ecologically. The key is to be persistent and to act early. While pest monitoring and pest prevention measures take time, these efforts can thwart costly and damaging full-blown pest infestations down the road. SFBG gardeners cultivate unusual, and in some cases, incredibly rare and one-of-a-kind plants. “Effective and efficient pest control strategies are essential in managing these plant collections. We can’t afford to take this lightly. We are really pleased to be able to accomplish our objectives with virtually no pesticides in both the gardens and our nursery, and we aim to keep moving in this direction.”
Fortunately the Garden has a robust internship program and dedicated volunteers to help. Tuesdays and Thursdays are volunteer work days, where individuals can join the “Green Team” to weed, mulch and care for the thousands of plants that make up the collections. It often takes a group effort to transform a problem area, and thanks to the garden’s regular and occasional volunteers, more areas are being renewed as weeds are replaced with beautiful horticultural displays. “While we haven’t grown in size, we’ve virtually doubled our holdings in the past decade. Practically every square inch of this place is actively gardened now. Folks who haven’t visited us in a while are amazed.”
In order to maintain this growing garden, workers rely on a combination of methods for pest control, ranging from mulching, physical removal, and green flaming for weed control to cultural practices for insect and disease pests. Sheet mulching with cardboard and fibrous plant materials like palm fronds is a favored practice for smothering weeds in overgrown areas, along trails, and in the spaces between plantings. Weeds are tolerated in some instances such as in small pavement cracks, but in the native garden, invasive European grass weeds are painstakingly extracted so visitors can enjoy a recreation of a pristine, authentic California meadow.
Very little synthetic fertilizer is used throughout the collections. Bob stresses how beneficial this practice is in reducing the numbers of insect pests since there is far less succulent growth and excess nitrogen in the foliage to attract them. “Over fed plants often lead to overfed plant feeders.”
“We have a diverse collection of floral resources with different flowering times that helps support pollinators and beneficial insects as well. Since we don’t spray, their populations thrive and we reap the rewards. We rarely have problems with insect pests requiring anything from us. Last fall we did experience a particularly bad Araucaria scale infestation and had planned to purchase cryptobugs as a biocontrol, in the spring. By the time the weather warmed up in February, the scale had all but disappeared. It’s often like that with insect pests here. By the time we figure out what’s going on and what to do, the pest is gone.”
Gophers, moles and voles, on the other hand, also inhabit the garden and are essentially omnipresent. Their feeding and burrowing activities wreak havoc with the turf and in the planting beds when their numbers are high. Coyotes, foxes, hawks and owls all do their part in helping keep populations in check by acting as natural predators, but control measures are still necessary. Rodenticides have not been used at SFBG for many years. Instead, the staff relies on a variety of traps to catch gophers and moles in their burrows. They concentrate much of their efforts early in the spring before breeding season.
Fiorello and the SFBG interns and volunteers have accomplished a great deal in transforming this urban oasis into a pesticide-free zone. Natural, least-toxic products are used sparingly for yellow jacket control in the garden and slug and snail control in the nursery when needed. Otherwise, “the plug’s in the jug” as Bob puts it. However things are changing, and global warming brings the threat of more pests, particularly soft-bodied insects like scale, whiteflies and mealy bugs. “We in the Bay Area are starting to experience what our friends and colleagues in the Central Valley and Southern California have been dealing with for years in this regard—bugs! And lots of them.”
Bob is also on the lookout for emerging invasive species and plant diseases, having previously dealt with Sudden Oak Death (SOD) and Pine Pitch Canker, which killed off several specimen trees and continue to be major problems in Golden Gate Park. Well aware that the botanical garden doesn’t exist in a bubble, the garden staff continues to research and learn new pest control methods as the need arises.
Aside from the opportunity to view unusual plants and the spectacular scenery of one of America’s most beloved public spaces, the San Francisco Botanical Garden offers visitors the chance to see IPM principles in action and to learn how to implement non-chemical methods for pest control at home. It’s something that has brought the SFBG much acclaim and attention over the years, but the man who has done the most to make this strategy a success takes it all in stride, “We are working with nature, not against nature… so we have this natural system that, with just a little help from us, pretty much takes care of itself. Really, how cool is that?”
You can find out for yourself by visiting the San Francisco Botanical Garden at Strybing Arboretum in Golden Gate Park. They are open everyday of the year at 9 am. For more information, visit their website at www.sfbotanicalgarden.org.
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