I stopped using Roundup herbicide years ago after learning about its devastating consequences. Is there a good substitute? I want something speedier and less unsightly than black plastic sheeting. And what's the right way to dispose of my leftovers?

—Ellen in Chicago

When I was a kid on a Wisconsin farm, I rode a tractor that hauled a big barrel of the herbicide 2,4-D. I loathed the odor of it then, and even more after learning it was an ingredient of Agent Orange, 12 million gallons of which the U.S. military dumped on Vietnam. However, even as a long-term enemy of pesticides, I cannot name a good spray-on substitute for Roundup or other pesticides whose active ingredient is glyphosate, the most heavily used herbicide on Earth.

The EPA declared glyphosate safe in 1991. But in March, the International Agency for Research on Cancer, an arm of the World Health Organization, classified glyphosate as a "probable" cause of cancer. As an alternative, you can try vinegar, corn gluten, pelargonic acid (a naturally occurring fatty acid), or clove- or citrus-oil sprays.

All that said, you might find yourself more satisfied with two labor-intensive solutions: hand weeding or "flame weeding" with a propane torch designed for gardening. The problem with flaming is that unless you cook the weeds early, you risk incinerating friendly flora.

For pesticide disposal, follow the instructions on the container. If you lack equipment for this process, consider it hazardous waste and contact your state or local pesticide or environmental control agency. Never pour pesticide down the drain or dump it.—Bob Schildgen