The trouble with poison oak, Dr. Martin Vale explained to the committee, was largely a misunderstanding.
The plant produced an oily mixture called urushiol. In human skin, its components reacted with proteins, giving the immune system something unfamiliar to attack. Much of the resulting damage was inflicted by the defense. It was an unfortunate chemical encounter rather than evidence that the shrub bore humanity any particular ill will.
“Nevertheless,” said the chairman, scratching beneath his watchband.
“Nevertheless,” agreed Vale.
Vale had spent eleven years studying the problem and had learned when an explanation was over. He advanced to a photograph of a firefighter on a ventilator.
Deer browsed on poison oak. Birds ate the berries. For humans, even getting rid of it could be dangerous: burning a patch carried the oil into the lungs of whoever stood downwind. The firefighter in the photograph had spent three weeks in intensive care. After that summer, Vale had little difficulty getting on the committee’s agenda.
He proposed an engineered plant virus. Its intended hosts were the urushiol-producing species the committee wanted removed: poison oak, poison ivy, and their close relatives. Preliminary tests had killed the target plants without damaging the surrounding vegetation.
“And it attacks only those plants?” asked the chairman.
“Those are the only hosts we’ve identified.”
The chairman underlined only.
“What happens when they’re gone?”
“Without a host, the virus cannot reproduce.”
The chairman put down his pen. A solution that disposed of itself required very little further discussion.
The funding was unanimous.
The field trials went beautifully. Treated plants withered among untouched grasses. Insects emerged unharmed, birds continued feeding, and the soil showed no troublesome residues. Vale’s team produced photographs in which the dead plants were circled, since otherwise it was difficult to appreciate how much better the landscape had become.
Spraying began across the Pacific Northwest that autumn. By winter, the results exceeded every target except complete eradication. Here and there, healthy specimens remained among their dead neighbors.
Vale requested funding to follow the surviving patches through another growing season. The program director returned his application with a question in the margin: were any of these plants sick?
Vale wrote that this was precisely what concerned him.
The director arranged for a grounds crew to remove them and closed the grant.
In March, a field technician brought Vale a cutting from one of the patches awaiting removal. She had carried it in a plastic bag on the passenger seat. She set it on his desk and stopped halfway through explaining where she had found it. When he offered her a chair, she shook her head, then sat down.
Vale called an ambulance. As the paramedics wheeled her out, she held her keys toward him.
“The car’s in a loading bay.”
He took them and told her not to worry.
Then he opened the bag beneath an extraction hood. The leaves were glossy and unmarked.
By evening, he had moved her car into a visitors’ space. The hospital called while he was still holding the keys. The technician had died; did he have a number for her family?
The laboratory found almost none of the familiar urushiol in the sample, which was briefly reassuring, and several unfamiliar compounds, which were not. One escaped readily into the air and damaged lung tissue directly. Previous sensitivity to poison oak made no difference.
For the first time in Vale’s career, the distinction between an allergen and a poison interested everyone.
The surviving plants still carried the virus. They tolerated an infection that had killed their neighbors, and within them the virus had continued changing. Their outward recovery concealed a substantial alteration in their chemistry.
Officials ordered the patches destroyed. Workers wore sealed protective equipment. Each site was fenced, numbered, and scheduled for inspection before the surrounding land could be reopened.
Then a woman died tending tomatoes in a greenhouse outside Portland.
Vale read the report twice before calling the attending physician.
“Any contact with poison oak?”
“Her husband says no.”
“Gardening equipment? Firewood?”
“She grows tomatoes, Doctor.”
Vale sent for a plant. It arrived in a sealed container, healthy and bearing fruit. His staff found a variant of the virus in its leaves, along with the compound that had killed the technician.
He checked the sample number against the shipping receipt, then asked them to run it again.
Further samples arrived from a nursery and an orchard. The altered virus could infect plants well outside its original host range. In those hosts, too, the infection changed what the plant produced. The concentrations varied. The substance did not.
Vale’s team began testing everything they could obtain. A negative result meant that a specimen was uninfected when sampled. It no longer meant that the species was safe.
Shipments were halted after the nursery stock had been delivered. Gardens were destroyed after the compost had been collected. Insects carried the infection across quarantine boundaries while committees negotiated where those boundaries should be.
The maps acquired circles, then shaded regions, then dates after which no reliable reports had been received.
At first, the emergency food program replaced contaminated crops with other crops. Later, its bulletins listed the remaining stocks of food harvested before the spraying began.
The chairman called Vale from an underground facility.
“You said it would run out of hosts.”
“It was supposed to.”
“What about the unaffected species?”
“We haven’t found one that stays unaffected.”
There was a pause. Vale could hear someone speaking in the room with the chairman, asking a question the chairman did not answer.
“Then stop them producing it.”
Vale looked at the sealed growth chambers beyond his desk. There had been a time when that request would have sounded like a grant.
“We’re working on it.”
“How long?”
Vale had an explanation, but he had learned when an explanation was over.
Outside, the municipal sprinklers came on at dusk, as programmed, to conserve water.
By summer, nothing on Earth was allergic to poison oak.