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You Can Use RoundUp (for lawns) on Your Grass This Summer!

by Allyn Hane 21 Jul 2020

Summer Weeds and Crabgrass

Summer can be tough on your lawn, and tough on you, too.

If you have cool-season turf, your lawn may be barely even growing right now, struggling to stay green, but one thing that is surely growing are the weeds.

If you have warm-season turf, for sure weeds are growing strong - they mirror the speed and strength of your St Augustine, Bermuda, Zoysia, or Centipede.

But all is not lost, you can make good progress and knock some, if not most of them back.

How Does Weed Control Work?

There are many weed controls that have an 85 degree temperature restriction on them.

What this means is you should not spray when temps are over 85 as you risk damaging your grass if you do.

When we spray the lawn for weeds, we are using a “selective herbicide” which means it will kill the targeted weed in the lawn and not visibly harm the lawn.

It’s “selective” about what it kills. However, just because you don’t see any visible harm to your grass, it doesn’t mean it’s not still causing some stunting or stress.

Most of the weed controls we utilize work systemically. This means they absorb into the plant and kill it from the inside out.

As an example, Dicamba is an active ingredient found in many of the weed killers we use.

It can be used on all cool-season turf and warm-season Bermuda, Zoysia, Centipede, and Bahia (very low concentrations ok for St Augustine too!).

Here you can see it listed in the very popular Bio-Advanced Weed control that is available at box stores and I have recommended for many of you.

Dicamba is an “Auxin” herbicide. It mimics naturally occurring auxin hormones in plants, but instead of healthy, normal levels of auxins that stimulate healthy growth, it causes rapid, extreme cell growth and disfigurement that kills the plant (weed) from the inside.

Think of it like overdosing the plant with steroids and growth hormone to the point where it dies. Gnarly right?

I bring this up because for the most part, turfgrass isn’t sensitive to this chemistry. But that doesn’t mean the grass plants are unaffected.

Think of this like you coming in contact with a virus. You may not develop any visible symptoms, you may only feel slightly tired for a day, but someone else in your household may be sensitive to that same virus and get sick from it.

But what if you were compromised and came in contact with it? What if you were tired and stressed from lack of sleep?

Maybe then your resistance to that virus would be weakened and you would suffer sickness from it. (I know this is a subject we are all very familiar with right now and so I hope you understand that this is just an analogy to open a window to your understanding of the lawn and weeds)

When your turf is stressed and tired from heat over 85F, the auxin herbicide dicamba can damage it. If it is stressed from insect or disease pressure, same thing, the herbicide can damage it.

This is why you will often see on labels “do not apply to stressed turf.”

I Recommend Spot Spraying

Not all weed killing chems have this restriction, but many do.

And because of this, I recommend that in summer, no matter what weed control you are using, you spot spray.

Just mark it down, as a DIYer, don’t blanket spray weed control in the summer.

Even if you waited until evening when temps are under 85, I still recommend you just spot spray.

And if you have Centipede or St Augustine, for sure you should spot spray. Those grass types will show some stunting in summer just from you telling them you are thinking about spraying! Ha ha!

And this is where the “Ready To Use” (RTU) pre-mixes come into play. These are 1-gallon jugs of weed control, pre-mixed for you.

The reason I am bringing these up is that they have gotten MUCH better in the last couple years.

I am going to give you recommendations based on grass type now, and I’ll start each of you, warm season and cool season, with an RTU formulation that I can bet you have been overlooking because of the brand name.

The brand name is “RoundUp for Lawns.” The reason you guys overlook it is because you associate the brand “RoundUp” with killing everything and you know to stay away from it.

That is because RoundUp as a brand made their name and built their business on using the active ingredient, Glyphosate which is a “non-selective” herbicide which means it kills everything.

Too much of it can kill large trees, it’s that powerful.

I’m pretty sure that brand is trying to separate itself from those old thoughts that you all have about them though, and nowadays, they actually make some excellent “selective” weed controls that will not harm the lawn, but will wipe out a good majority of weeds and problem grasses in your lawn. (this is not sponsored)

With that, here are some recommendations for you depending on grass type.

Warm Season Lawns

Bermuda, Zoysia, St Augustine and Centipede

The RoundUp for Southern Lawns is available at pretty much every Home Depot or Lowes in the South. Here is what it looks like:

This will knock back most of what we are seeing here in the summer.

Spurge is a big one and it’s decent on that. Dollar weed in the wet areas, same thing, does pretty well. Chamberbitter, smokes it.

I will tell you though, no matter what, spray this in the evening when temps are under 85 and if you have St Augustinegrass, you will probably see some collateral damage - but that is why we are spot spraying!

It’s ok to take a little damage in the process of eliminating weeds.

Either way, the active ingredients in this product are quite impressive even if they are in lower concentrations.

This product is pretty thick - almost like syrup, so don’t expect it to come out in a fine mist.

Instead, you use it to coat the weeds and it will also have some uptake by plant roots.

Remember, you do not have to wipe out 100% of the weeds this summer - just make progress. Killing 10% of the weeds in the lawn is better than killing none. Make sense.

The hope is that you are also pushing your warm-season turf to grow right now. This will help your turf help you by filling in where weeds die.

Need Something Stronger?

Need something stronger that kills more weeds?

Then go with Celsius.

It is by far the best all-around weed control that is available to homeowners with warm-season turf.

It’s $129 for a small bottle but it’s a “WG” product (wettable granule - dry material you mix in water) and it goes a long way.

It has an extremely low use rate of .113 oz/gallon/1,000 sq ft which means that bottle covers 88,000 sq ft!

It gets just about everything, including doveweed and is pretty easy on turf.

It doesn’t have a temp restriction but I still recommend you spray in the evening. However, it will not kill sedges like kyllinga.

Nutsedge and Kyllinga

However, there is one weed infestation that we face in summer that it is terrible on and that is nutsedge and kyllinga. Yellow nutsedge is listed on the label of the RoundUp for lawns, but I can tell you, it won’t work on that.

Good news here is we have a product that is inexpensive and VERY easy on turf that can be sprayed with no temp restrictions and it will kill sedges and kyllinga in summer.

You can blanket spray it in fact. Just know, it works slow - takes a good 21 days to kill. That product is active ingredient Halosulfuron-methyl.

There is a brand name called “Sedgehammer” but now it’s available in generics and it’s also available in small, 1-gallon use packets.

I have used Sedgehammer for many years and it works great, just slow. You can spike it in with other liquid apps you are doing too.

So if you are blanket spraying insect control, you can also spike the Sedgehammer in with it. Or you can mix and spray it by itself, no worries.

If you get the single-use, 1-gallon packet, it already includes surfactant in the mix.

If you get the larger bottle, we do recommend you get some non-ionic surfactant to go along with your mix.

Either way, this is safe for all grass types (bahia too), no temperature restrictions and you can blanket spray it, just know, it works slowly.

Cool Season Lawns

I also have a spot spray, “ready to use” option for you and it is the RoundUp branded jug.

They have done a good job with this one too. It’s pretty well rounded, here are the active ingredients:

You can use this on Kentucky Bluegrass, Perennial Ryegrass and Turf Type Tall Fescue (also ok for zoysia and bermuda).

The quinclorac in this mix will knock down crabgrass, but only if you get to it early! You will probably be seeing it pop up right now.

It will take 2 treatments, 14 days apart and you will see it around the edges in the “heat zones” before you see it anywhere else.

Here is a full video on crabgrass from “back in the day.”

It will also do pretty good on foxtail which is another one you will be seeing waving at you this time of year.

Now don’t expect miracles from this product - but what you can expect is it to work well as a spot spray to clean up a few weeds here and there. Use this to patrol the lawn on weekends and spot spray what you see.

Need Something Stronger?

Quincept is excellent. It has higher concentrations of quinclorac for stubborn, more mature crabgrass and 2,4-D (13.24%), and dicamba (1.38%) for most other broadleaf weeds.

When I worked for TruGreen, this was our go-to summer weed control but nowadays, the prices have come down and it’s pretty affordable for a homeowner. A quart (32oz) is $56 on DoMyOwn.

The mix rate is 2.6 oz/gallon/1,000 sq ft so the quart will cover 12,000 sq ft.

Note: It will not get sedges, but it is good on clover, thistle, spurge and foxtail.

If you see sedges in your lawn, read the section above about sedges and kyllinga. That product is great for you guys too.

Ground Ivy, Clover, and Violet
I get tons of emails about these three weeds in cool-season lawns.

In the past, I would have told you to attack ground ivy and violet in the spring and fall and leave it alone in the summer.

However, if you have a really bad infestation, and you just can’t stand it anymore, then the very best weed control you can get is Sure Power. It works great in the heat of summer.

Now I know, it’s expensive, and for 99% of you the investment will not be something you want to make.

However, I know there are a few of you who really want it gone and this product will do that.

Lots of info in this one I know, but I wanted to give you some options.

The key with weed control is to eat the elephant in small bites.

Don’t think you need a miracle product to kill everything in one application.

Especially in summer, spot spray where you can and keep the lawn properly irrigated and moving to help you along the way.

Be sure to subscribe to my podcast where I am able to go into these concepts in a little deeper detail and talk through strategies and for each season and each part of the country.

I’ll see you in the lawn!

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