Guide To The Best Weed Killer For Lawns

When you’re working on developing the best possible lawn, there are few things as annoying as having weeds pop up. With deep root systems, hardy constitutions and other characteristics that make them difficult to control, weeds are often the bane of the diligent homeowner’s yard when they’re allowed to get out of hand. Let’s take a look at different weed killers, how they work and figure out what the best weed killer for lawn will be.

What’s The Problem?

Before you can figure out what the best weed killer is for your lawn, we need to figure out what weeds you have. Are they broadleaves or undesirable grasses? Broadleaf weeds are easier to eliminate as they have a different mode of action in their growth mechanisms, so you can spray a broadleaf herbicide on them without harming the grass growing nearby too much. You can use either preemergent or postemergent on broadleaves, but overdoing it may result in brown or yellow spots in your lawn while nearby or oversprayed grass recovers

Weedy grasses, on the other hand, take a bit more care. Because they have more in common with the turf grass you want in your yard, it becomes much easier to accidentally damage the turf grass you’re trying to keep. To treat these weeds, you’ll need to either use a preemergent herbicide to kill them prior to the desired grass emerging, use organic methods that don’t cause much damage to nearby plants or be willing to deal with the brown or yellow spots that often occur as nearby grass is also damaged.

Modes of Action

Different herbicides have different modes of action that can be more effective on particular types of weeds and should be considered when figuring out the best weed killer for lawn problems. Purdue University has a much more in-depth guide to the best weed killer for lawns, but here are some basic modes of action and common herbicides associated with them:

  • Auxin Growth Regulators: Auxin is a plant hormone that controls growth. After treating a plant with a herbicide from this category, the plant will begin to deform and have significantly different growth patterns than it did prior to treatment. Eventually, the growth will kill the plant by restricting nutrient flow, restricting photosynthesis surfaces available to capture sunlight and similar modes, making it effective against biennial and perennial weed problems. Common herbicides used in this category include Phenoxyaliphatic Acid in 2,4-D, Benzoic Acid in dicamba and Picolinic Acid in picloram, clopyralid, triclopyr and fluroxypyr.
  • Aromatic Amino Acid Inhibitors: Amino acids are used in maintaining the plant’s photosynthesis production, so using this class of herbicide on the foliage will quickly causes leaf damage, including yellowing and death, starving the weed. Glyphosate, the primary ingredient in Roundup, and sulfosate are the two herbicides in this broad-spectrum herbicide. Because of its range, this is one of the best weed killer for lawn issues that most homeowners face, as they deal well with a wide range of plant types.
  • Branched Chain Amino Acid Inhibitors: Much like the previous category, this herbicide class stops growth at shoots and roots. It causes yellowing and discoloration of the plant treated, but take a few weeks for the effects to become apparent. They include Imidazolinones such as imazquin and Sulfonylureas such as chlorsulfuron.
  • Photosynthetic Inhibitors: These herbicides include a number of chemicals that destroy a plants’ photosynthesis capabilities, essentially starving it. Some of them are restricted to trained applicators. This class includes Triazines such as atrazine, Uracils such as terbacil, Phenylureas such as linuron, and a few other individual compounds that fall into the class because of their mode of action.
  • Cell Membrane Destroyers: With a very fast mode of action, these herbicides, when combined with sunlight, cause the cell membrane to be destroyed, killing the plant. Bipyridyliums such as paraquat specifically target stem material and Bentazon is a single chemical in its own family within this class that is effective against annual broadleaves, yellow nutsedge and shoot removal for perennial weeds.
  • Root Cell Division Inhibitors: As a preemergent herbicide, this class prevents weeds through application before your intended grass starts growing for the season: late spring for warm weather grasses and early spring and late summer for cool season grasses. They include Dinitroanilines such as prodiamine which is known commercially as Barricade and inhibits root growth.

Organic Methods of Weed Control

Though there are some options for an organic weed killer for lawns, staying on top of getting weeds out of your yard before they seed is the best route to prevent major outbreaks. For biennial plants such as thistles, Queen Anne’s lace and other plants with a deep taproot, watering the area before pulling weeds will make them much easier to remove. Pouring boiling water on the plant, burning it back with a propane torch or keeping it trimmed back to the stem will cause enough damage and starve it badly enough to kill it, though it may take several treatments.

There are two specific organic weed killers that can work well, but you need to use them with caution. Salt can be used to kill weeds, but it may affect plants you want to keep, so it’s best kept to keeping walkways, driveways or patios weed-free. Examples of what happens when there’s too much salt in the soil are the fall of the Babylonian and Aztec empires, who used salt-heavy fertilizer water and eventually ruined their soils, causing starvation.

The acetic acid in vinegar is another great organic weed killer. Pour straight vinegar into a spray bottle and wet the leaves of the weed you’re trying to get rid of. Adding a few drops of Dawn dish soap or other hardy grease-cutting dishsoap will help the vinegar get into closer contact with the leaves by breaking down the waxy leaf surface. Some tough weeds, such as thistles, will require repeated sprayings every couple weeks as they send new leaves out. Because it dissipates within a couple days, and even faster in the presence of water, don’t spray before a storm or your efforts will wash away.

So what is the best grass and weed killer? As you can see, the question is not so simply answered, as the best weed killer for lawns will change based on your circumstances. Take into consideration the type of weeds you are having problems with, your environment and the time you can commit to keeping weeds under control. This makes determining the best lawn weed killer for your situation much easier to figure out.

About the author

Matt Hagens

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