HERBICIDES
Use herbicides as a last resort—when nothing else works on a particular weed or when your lawn is completely overrun. And follow directions carefully. Used incorrectly, herbicides can injure or kill turf and other desirable plants.

If you use an herbicide, choose one that's labeled as safe for the type of turf you're growing and effective against the weeds you've got. The label states when and in which conditions to use the product. Some herbicides work only within a certain temperature range; others work only when applied at a specific time of year.

Herbicides fall into three major categories:

Preemergence herbicides kill germinating seeds before seedlings break through the soil. Crabgrass is the primary target. The most common preemergence herbicides are synthetic. Natural, nontoxic preemergence herbicides made from corn gluten are safer, though you might have to apply them for several seasons for them to be fully effective. Three quality products are Concern Weed Prevention Plus, WOW! and WeedzSTOP. A drawback to these and most other preemergence herbicides is that they kill germinating lawn seed. Check product labels carefully.

Postemergence herbicides kill existing weeds that are actively growing. These come in two basic forms: contact and systemic. Contact herbicides kill only the part of the plant they touch. Most act quickly and work best against annual weeds. Systemic herbicides circulate inside the plant, killing the whole thing. They're more effective than contact herbicides on perennial weeds, though repeat treatments might be needed.

You also need to choose between selective and nonselective versions of systemic herbicides. Selective herbicides kill only certain weeds, while nonselective herbicides kill any green, growing plant, whether it's a weed or not. Most broadleaf herbicides, including products like Weed-Away and Weed Warrior, are systemic and selective to kill broadleaf weeds only. They won't kill weedy grasses. Glyphosate—the active ingredient in Roundup and other products—is an example of a systemic, nonselective herbicide that kills broadleaf weeds and weedy grasses. But because it also kills turf and other desirable plants, it's safest to use it on your lawn when you want to kill an entire section and then replant it. Finale, in which the active ingredient is gluphosinate ammonium, is another nonselective used for this purpose.

When using any postemergence herbicide, don't apply them over your entire lawn, if possible. Instead, spot-treat isolated weeds or weedy patches.

Weed-and-feed products combine fertilizer and herbicides to do two jobs at once. But their promised labor savings can backfire if the recommended time for weed control doesn't coincide with the best time and rates for fertilizing. Most also pose an herbicide-overdose risk when used for follow-up fertilizing. WOW Plus!, corn gluten with added organic fertilizer, is the safest weed-and-feed.

Whichever herbicide you use, follow the directions. Address the causes of weeds at the same time to keep new ones from growing. And reseed the bare spots left by dead weeds. The bottom line in the war against weeds: Care for your lawn and apply only what it needs—and only when necessary.
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