It was the fall 2008 election season in Washington, D.C., and the smell of possibility was in the air. Unfortunately, that wasn't the only smell around.
All over town, GINKGO TREES were dropping their malodorous fruit, a yellowish grape-sized berry, all over the sidewalk. Unsuspecting pedestrians crushed the berries underfoot, releasing a putrid bouquet containing butanoic acid, an acrid-tasting compound that also turns up in vomit.
The stench was the result of a setback in controlling the ginkgos' fruit production at the District's Urban Forestry Administration, which plants and maintains the city's street trees. Local bloggers raised a stink over the fetid fruit and dubbed the scandal Ginkgogate, as only Beltway insiders can.
The ginkgo is an ancient tree with elegant, fan-shaped foliage. Ginkgos can be male or female, but only the females produce fruit, explains John P. Thomas, associate director of Urban Forestry for the District. The capital has about 6,000 female ginkgos, the legacy of a planting project that took place before experts could tell the sexes apart at the sapling stage, he says.
Instead of removing the trees, the city decided to block their fruit production by spraying them with Sprout Nip, a plant growth regulator containing chlorpropham, which is a carbamate that affects plant mitosis. But spraying isn't a simple fix—the process requires lots of equipment, such as spray trucks, and needlessly exposes a tree's surroundings to the chemical. What's more, timing is essential for the spray to work. The exact window in which chlorpropham works best varies in different pockets of the city, complicating the situation, Thomas says.
A few years ago, District workers began testing an alternative—dikegulac-sodium, a sugar derivative that blocks DNA synthesis. Dikegulac can be given to trees in a variety of ways, from spraying to simply pouring it at the base of a tree, says Gary Custis, manager of field research and technical services at PBI/Gordon, which sells dikegulac under the name Atrimmec.
The District opted to use specialized needles to deliver small amounts of dikegulac just under ginkgo trees' bark. In smaller scale tests, the injected dikegulac was as effective as Sprout Nip at blocking ginkgo- berry formation. So in 2008, officials decided to try it citywide.
The fruits of that labor turned out to be rather more pungent than anyone had expected. "To this day, we aren't sure what went wrong," Thomas says. Countless factors may have been at play, from temperature variations to the exact method of injection, he adds.
"It may have come down to timing," speculates Chip Doolittle, president of ArborSystems, the company that sells the dikegulac product Pinscher, which the District used. As with Sprout Nip, there exists a precise window where Pinscher will work best.
"Working with plant growth regulators is definitely not a cookie-cutter thing," says Jacqueline K. Burns, who studies plant physiology at the University of Florida Citrus Research & Education Center. "Environmental conditions may not be conducive to the same effect every year."
The District hasn't given up on Pinscher, Thomas says. Although his department sprayed Sprout Nip this year, they're back to tinkering with Pinscher so they can figure out how to make it work. "Understanding the use of these chemicals and delivery systems is a big untapped market," he says.