Q: Hi Steve, we have a problem with dollarweed in low parts of our yard that stay wet. We've tried some weed killers but even at low concentrations, our St Augustine (much of which is Floratam) the grass seems to be affected more than the weeds. I found a new weed killer "Image" with 4% Atrazine that says it's safe for all St Augustine grass. Is this safe for Floratam? Is it too late in the season to use it? It seems this time of the year is when the dollarweed really takes off. We don't water these areas unless we're into a real drought, so we can't do much about the wetness. Any suggestions would be greatly appreciated.
Don Taylor, Panama City, FL
A: Dollarweed -- which gets its name from shiny, green leaves that are the shape and size of silver dollars -- is the main scourge of St. Augustine lawns in the Coastal South where the grass stays wet. It's perennial, spreads rapidly, and hard to pull up. Atrazine is the most effective herbicide to use against it. As long as you follow label directions, it's safe for St. Augustine.
Unfortunately, atrazine isn't safe for hardly anything else. It's soluble in water, so it moves rapidly through the soil following rain or irrigation. When it contacts roots of flowers, shrubs, and trees, it can injure or kill them. It's very toxic to fish if it gets into a pond or stream. And it has become a major pollutant of groundwater in the South. Many cities now test for it as a contaminant in drinking water. If it were up to me, I'd ban its use entirely.
So what about the dollarweed? Without atrazine, the only thing you can do is water less often, try to get the soil to drain better, and core-aerate your lawn at least once a year to reduce compaction. I have heard some people say they've had luck with wetting the dollarweed foliage and then sprinkling baking soda on it, but I've never tried it, so I don't know if it works.