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Selective Herbicide for Grass | What Is It and How Does It Work?

When unwanted weeds and plants grow on the lawn, sometimes hand removal is no longer viable, and you may need to get a selective herbicide.

There are so many different types of weed killers available in the market. However, you cannot just start applying the herbicide you got from your local garden supply store and expect it to solve your lawn weed problems.

You need to arm yourself with the proper information to avoid disasters. 

If you choose to use chemical lawn care products, how do you decide whether to go with non-selective or selective herbicide?

Using the wrong product or not correctly timing its application could make your efforts unsuccessful or even disastrous.

Gardener applying selective herbicide to a lawn

If you have an accident while using selective herbicide or your lawn is too far gone, check out our Instant Lawn Hobart Service page. We can transform your yard in 3 days or less.

WHAT IS AN HERBICIDE?

Herbicides are lawn care products, whether synthetic or natural, used to kill weeds by stopping the plant’s metabolic processes. They usually come in liquid or granulated form.

We use herbicides to eliminate unwanted vegetation. On the lawn, that means getting rid of weeds that compete with our turf for nutrients and make the yard less attractive.

Herbicides can either be contact or systemic:

  • Contact herbicides only react to the part of the plant that it touches. 
  • Systemic herbicides get absorbed by the plant through its vascular system so that it kills the entire plant.

Non-selective Herbicide

Non-selective herbicides, also broad-spectrum herbicides, will kill any vegetation it touches.

Broad-spectrum herbicides are not formulated to target specific weeds, therefore will destroy any living plant in or around the area of application.

You may use non-selective herbicides when you are sure that you do not intend to keep any plant wherever you apply it.

The most common non-selective herbicides are glyphosates, which can kill weeds as well as your turf.

Selective Herbicide

For unwanted weeds on the lawn, the selective herbicide is a better choice. If you choose correctly, you can target specific weeds while sparing your precious lawn.

How does a selective herbicide work?

Selective herbicides are formulated to destroy specific vegetation because they are made to act on a certain plant’s metabolic process, particular to different types of plant and even growth stage.

Selective herbicides may be classified depending on how they act to kill weeds. Some selective herbicides are root inhibitors, others are synthetic growth regulators, and the strongest are those that are inhibiting protein synthesis.

Root Inhibitors

Pre-emergent herbicides are root inhibitors. They work to block the cell division and the formation of the cell wall in the emerging root tissues.

With root inhibitors, the seeds cannot take root, and the weeds cannot grow.

Root inhibitors are applied before the weeds sprout or “emerge” from the ground. The usual time for this is before the growing season, which for many types of weeds is at the early part of spring.

Synthetic Growth Regulators

Synthetic growth regulators are post-emergent herbicides. This weed killer is applied when the weeds have already emerged from the soil—when you can already see them.

Synthetic growth regulators affect certain functions of the weed’s growth to prevent it from growing, which will eventually kill it.

Selective herbicides for broadleaf weeds, for example, will cause those weeds to have unusual growth patterns. 

The synthetic growth regulator in broadleaf herbicides causes blockage on the weeds’ circulation, resulting in the speedy death of the weeds.

Inhibiting Protein Synthesis

More potent herbicides inhibit protein synthesis in the weed. Protein synthesis is an essential metabolic process for the growth and survival of living things.

When protein synthesis is prevented, it will kill the target weed. This type of herbicide is formulated to kill specific weeds by blocking the pathway within that particular weed’s protein synthesis but allows others to continue, therefore sparing other vegetation.

These types of selective herbicides are used on more resilient broadleaf weeds and sedges.

Choosing the Right Selective Herbicide

Choosing the right herbicide requires diligence. Be fully informed before making a choice and using it on your lawn.

Know the specific weeds you want to eliminate

If you will choose to use a selective herbicide, then the most critical information is what type of lawn weed you are trying to eliminate? The choice of a selective herbicide very much depends on the target weed. Check our Lawn Weeds Guide for help with identification.

Next is to determine the life cycle and growth habits of the weeds. If you will use a pre-emergent selective herbicide, for example, timing is crucial. Find out when the weeds germinate so that you can apply your herbicide before that.

Knowing the type of weed will also help in the timing of a post-emergent selective herbicide.

Know your lawn

In addition to getting as much information about your target weeds, it is crucial to take into consideration the type of grass you have. 

While selective herbicides are formulated to target specific weeds, they are also made to either affect or be tolerated by certain grass types.

For example, a post-emergent with dicamba will harm Buffalo grass. Bromoxynil may be safer and not kill Sir Walter and other Buffalo grass. 

Bromoxynil is also tolerated by Bent, Kikuyu, Fescue, Rye, and Couch.

Selective herbicides with halosulfuron-methyl are effective against Mullumbimby Couch and nutgrass, while Sir Walter and most lawn types can tolerate it.

Endothall is effective against Winter Grass and relatively safe for Common Couch, Blue Couch, Buffalo, Bent, and Brown Top lawns.

Tips When Using Herbicides

After you have chosen the right herbicide for your needs, you need to keep in mind the following things:

Read the instructions carefully

Read, read, read and understand before applying the herbicide. 

Make sure that you know what herbicide you are using, what it is for, when you should apply it, and the manner of application.

You cannot use pre-emergent herbicides on already mature weeds. 

You need to get the right kind of selective herbicide that will kill the lawn weeds without harming your turf.

Measure well and make sure that you mix the herbicide according to the instructions.

Safety First

When handling strong chemicals like herbicides, you need to practice safety and precaution. 

Wear proper personal protective equipment or PPE such as glasses, gloves, long-sleeved shirts, long pants, and closed shoes.

Keep small children, pets, and other people at a safe distance from the area of application before, during, and a few days after.

Mind the weather and wind patterns

Some herbicides need to be applied when the lawn is dry, or it may need to be kept dry for several days. Make sure to check on the forecast to ensure that there is no rain around the days you plan to use it.

Another consideration is wind and wind direction. Spraying herbicides with blowing winds may take the product where you do not want it.

Have a dedicated applicator and container

If you have different lawn care products, it is better to have separate containers and applicators for each.

By keeping them separate, you will not run the risk of having residues of other products in a container.

Use a separate container for selective herbicides to avoid the risk of leaving some residue of the non-selective herbicide.

If you do not use separate containers and applicators, the residual broad-spectrum herbicide may end up harming plants or grass you did not intend to kill.