Question: I have used a broadleafed weedkiller to try to get rid of this weed all season long. I still have it. What can I do? (Note from Neil: Several readers asked similar questions.)

Answer: This is sheep sorrel. It’s a weedy form of oxalis, and it’s really tenacious. I would continue to use the broadleafed weedkiller. We have no product that is any better for oxalis. However, I’d offer these suggestions. First, include one drop of liquid dishwashing detergent with each gallon of spray that you mix. That will hold the spray on the waxy leaf surfaces. Use a pump sprayer and not a hose-end sprayer. You’ll be able to apply smaller droplets that way, and again, they will hold onto the leaves better. Do not spray before or right after you mow your lawn. You need as much leaf surface as possible to absorb the 2,4-D broadleafed weedkiller.