Q: I want to use Drive XLR8 herbicide to control crabgrass. The label says I need a crop oil adjuvant. What is that?

A: An adjuvant is a chemical added to a pesticide to make it work better. Some gardeners add a drop of dish soap to their pesticide sprayer to cut water’s surface tension and help the herbicide spread across waxy leaves. Methylated seed oil makes the chemical in Drive stay on the leaf surface longer, causing better weed kill. At this time of year, though, I don’t think you need to kill crabgrass. The weed has already dropped thousands of seed in your yard. Your best bet for crabgrass control is to apply a pre-emergent in March next year to prevent crabgrass seed germination.