Using herbicides safely

If you use selective herbicides on your lawn, it's important to ensure that weeds, not desirable plants, receive the right dose at the right time. Herbicides can reach the wrong plant in a number of ways, most obviously by misdirected spray. Wind can also carry droplets to nearby plants, and sunlight can actually cause volatile products to drift about on warm days.

No matter the chemical you're using, review and follow all label directions and cautions. Here are some usage tips for specific types of herbicides:

"Weed-and-feed," or granular, herbicides

These herbicides are intended to be used only with a drop spreader.

• Before application, determine the correct setting by calibrating your spreader. Never apply granular herbicides with broadcast-type spreaders.
• Use granular herbicides if susceptible weeds are distributed throughout your lawn; avoid applying herbicide where there are no weeds.
• Apply only when the lawn is wet, such as by dew in the early morning. The moisture is necessary to activate the herbicide. After application, don't water for at least 24 hours (postpone application if rain is likely within 24 hours). Apply when air temperatures are between 60 and 90 F.
• Wear gloves, eye protection, long sleeves, and any other items noted on the label. Afterward, wash clothes in a separate load.

Concentrated liquid sprays

These products are designed to use in both hose-end and tank-type sprayers, but we strongly recommend the latter for their more accurate dilution and application.

• Double-check dilution rate and units used: "Tbs." is the abbreviation for tablespoons, "tsp.," teaspoons. There are 3 teaspoons in 1 tablespoon, and 2 tablespoons in 1 fluid ounce.
• Do not spray over exposed roots or leaves of nearby trees or other desirable plants, and avoid spray drift by applying only on calm, dry days when temperatures are between 55° and 90 F. Do not apply when rain is expected within six hours.
• Follow precaution directions on the label. You may have to wear water-impermeable gloves as well as long sleeves, rubber boots, and eye protection. After spraying, change clothes and wash the used ones in a separate load.

Herbicide types

Herbicides are classified according to their use or mode of action:

Nonselective herbicides like Roundup kill all kinds of plants.

Selective herbicides like Ortho Weed-B-Gon Max Weed Killer for Lawns Concentrate kill some plants but not others, when applied as directed. In lawns, selective herbicides kill types of plants that botanists call dicots. These have branching veins in variously shaped leaves and include many common lawn weeds. Monocots, which have parallel veins in typically narrow leaves, include most grasses.

Post-emergent herbicides such as Roundup and Weed-B-Gon kill growing weeds and may be either selective or not.

Pre-emergent herbicides prevent some weed seeds from even germinating. They are typically used in lawns in early spring to prevent crabgrass. Most often these herbicides are combined with a fertilizer, as in Scotts Turf Builder Halts Crabgrass Preventer.