You think you have problems with ragweed? In "The Happening," the stupefyingly silly new eco-thriller from M. Night Shyamalan, the plant world rises up against humankind, releasing an airborne toxin that causes mass suicide to sweep the East Coast. After an ominous first act, the film dies on the vine.

In an opening of Hitchcockian suspense, pedestrians in New York's Central Park become disoriented and halt in their tracks, then begin acting in bizarre, self-destructive ways. The effect is almost punctured by an onlooker's awkward dialogue ("Are those people clawing at themselves? That looks like blood!"), but a sequence at a nearby building site where construction workers leap to their death evokes grim memories of 9/11. The "event" initially is considered a terrorist attack, but as more and more neuro-toxin outbreaks are reported, it becomes clear that something else is at work.

Mark Wahlberg plays a high school science teacher who flees the city with his wife (Zooey Deschanel) and the daughter of a friend in tow. They avoid population centers, prime targets for the contagion, heading for smaller and smaller towns as the mind-scrambling poison nips at their heels. Soon they're running for remote farmhouses and casting worried looks at the wind-rippled trees. Creating an environmental horror story with vegetation is harder than it sounds. Imagine "The Birds" without birds and you have a fair idea of the circumstances.

As the film progresses, we're subjected to dozens of grisly deaths, most shockingly a man wandering into the lion exhibit at the Philadelphia Zoo. But the focus stays on Wahlberg and Deschanel, whose marriage is under some strain because of a mild flirtation.

The attention paid to their piddling relationship woes vs. the entire fate of humanity is absurd. We never feel persuaded that they have a bond, much less invested in seeing them patch it up. They just seem to be competing to see who can deliver the least convincing line readings. Deschanel's emotional tone is all over the map, irrationally chipper one moment and shell-shocked the next. Wahlberg, so impressive in "The Departed," fares no better. A scene in which he has a tense conversation with a houseplant is a shoo-in for the most ridiculous minute of screen time to be filmed this year.

The twist ending that was a fixture of earlier Shyamalan films is absent here. In fact, there's hardly a finale at all, merely a lazy coda that brings the situation full circle. "The Happening" never should have happened.

Colin Covert • 612-673-7186