NEW ORLEANS — A stinky but handsome and widely popular landscape tree has become an aggressive invader. Callery pears create dense thickets that overwhelm native plants and bear four-inch spikes that can flatten tractor tires.

Bradford pears and other ornamental Callery pears were cultivated from an import that saved pear orchards from a deadly fungus. And for decades, the decorative trees seemed near perfect, aside from a tendency to fall apart after about 15 years — and their stench. But they cross-pollinated with other ornamental varieties.

Invasive stands now have been reported in more than 30 states. Fourteen states, including Missouri, have formally listed the trees as invasive.