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IF
Using Lawn Herbicides,THEN Be Sensible About It
You shouldn't need to apply an herbicide or weed killer to your lawn, IF your lawn is properly maintained. Mowing at the right height and frequency, fertilizing with the right amount at the right time, and watering according to grass needs not homeowner ease, are key to proper lawn maintenance. That said, there are plenty of lawns around town that are full of weeds. Weed control options for homeowners with established lawns are hand pulling, mowing, and applying herbicides. Hand pulling weeds shouldn't be dismissed as absurd. A frequent weed check of the lawn may reveal a single species starting to invade, so pulling the few weeds before they proliferate makes good sense. Mowing the lawn before weeds flower and set seed also minimizes the spread of weeds. Some broadleaf weeds are killed over time just because their growing points are continuously mowed off. Unfortunately hand pulling and mowing won't get rid of all weeds, especially when weeds are present in abundance and the lawn is weak in stand. So what about using herbicides? Herbicides for Broadleaf Weeds: The easiest weeds to control in grass lawns are annual broadleaf weeds. Perennial broadleaf weeds can also be controlled, but it sometimes takes additional effort. Some common annual broadleaf weeds include bur clover, filaree, prickly lettuce, shepherds purse, and sowthistle. Common perennial broadleaf weeds are dandelion, white clover, creeping woodsorrel or oxalis, and plantains. There are oodles more broadleaf weeds. Many products are available and formulated for specific weeds or for use on specific turfgrass species. Generally these weed killers are postemergent, systemic herbicides containing combinations of two or three active ingredients, such as dicamba, mecoprop, or 2,4-D, and are very effective in controlling numerous broadleaf weeds. Some brand names are Trimec Lawn Weed Killer, Spectracide Weed Stop, Ortho Weed-b-Gon Weed Killer for Lawns, and Bayer Southern Weed Killer. There are many others that are similar, like Monterey Weed Whacker, so read the labels for their active ingredients and choose your favorite brand. If you have a warm-season lawn such as bermudagrass, hybrid bermuda, or St. Augustine, then be sure to purchase the right formulation or make sure that the label says it is safe to use on these lawn types. Triclopyr (Turflon) is also an effective broadleaf herbicide (especially good on oxalis) and is quite safe to use on cool-season lawns such as tall fescue. However, it will cause injury to bermudagrass and other warm-season lawns. Herbicides for Grass Weeds: Annual grasses such as crabgrass and annual bluegrass (Poa annua) can be effectively controlled in established lawns with preemergent herbicides such as benefin, bensulide, dithiopyr, oryzalin, pendimethalin, and prodiamine. Trade names such as Amaze, Crabgrass Preventer, Halts, Pendulum, Weed Stopper, Barricade, and Dimension may sound more familiar. The key to success is to apply the herbicide 2 to 3 weeks prior to weed germination and to thoroughly water the herbicide into the lawn. It may take three applications per year (early fall, late winter and mid-spring) to clean up a Poa annua and crabgrass weed infestation, but herbicides should not be needed year after year if cultural practices are modified to favor the turfgrass. It is much more difficult to control weedy grasses with postemergent herbicides. Products containing CMA (Ortho Crabgrass Killer), DSMA or MSMA (Weed-Hoe) reduce crabgrass and dallisgrass infestations, but not as effectively and several applications are needed in summer and in subsequent years. Some perennial grasses such as bermudagrass growing in a tall fescue lawn can be suppressed with repeated applications of triclopyr (Turflon), but are nearly impossible to eliminate, and a nonselective systemic herbicide such as glyphosate (Roundup) may be the last resort. Herbicides for Sedges: Yellow and purple nutsedge can be killed with spot treatments of glyphosate, alternatively you can make two applications with halosulfuron (Manage) or you can repeatedly spray with MSMA or bentazon (Nutgrass Nihilator). The latter is only effective on yellow nutsedge. No preemergent herbicides kill nutsedge tubers in turfgrass. Weed and Feed Products: Some fertilizer products contain either preemergent or postemergent (or both) herbicides for weed control. Use these combination products only when the lawn has a known weed problem and not every time you fertilize. Be sure the active ingredient in the product is one that will control the weed species causing your problems and also that the timing of the application is right. Tree safety: Also be aware that certain broadleaf herbicides, such as dicamba and triclopyr, can be absorbed by tree roots growing in lawns and may cause tree injury if applied too close to the tree dripline. Precautions are always listed on the herbicide label. Visit the MG website for more free information about lawns. Check
out the new interactive tool called UC Guide to Healthy Lawns.
It's useful for homeowners and professional gardeners alike. March 11, 2004 |