Crabgrass

Asked March 23, 2015, 4:11 PM EDT

Hello, I have been waging losing a battle against crabgrass in my lawn for years. I have tried several times to totally restart the lawn, killing all vegetation in the fall with Roundup, adding new soil in the spring, tilling, seeding, fertilizing, applying herbicides later. However, by the end of every summer, the crab grass has returned and taken over the lawn. What advice would you give? I have read about a pre emergent herbicide called Tupersan is not only very effective, but does not interfere with the planting of new lawn seed. Is this the best choice? Secondly, what would you recommend as the proper herbicide later in the season to prevent the crabgrass from returning. Finally, what seed would you suggest that might stand a better chance of winning the battle against this weed? Thanks

Montgomery County Maryland

11 Responses

First, spring grass does not have much chance of surviving well over the summer. It does not have much root system and cannot withstand the high temperatures (which are only getting higher) and the droughts that we almost always have in Maryland.
So, the best strategy is to sow a lawn in early fall (late August or September). That way, the tender new grass has three complete seasons, fall, winter (yes, roots grow on milder winter days), and spring, before the grass has to survive a Maryland summer.

You don't mention whether this is a sun or shade lawn. Big differences, different grasses. See this website pub for guidelines on growing lawns, including seed selection: http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG102%20Lawn%20Estab...

In order to prevent crabgrass germination, use a preemergent in the spring. You will also have to apply again later in the summer, because crabgrass seed continues to germinate all summer when weather conditions favor it. Weather conditions are a big determination in whether we have a lot or a little crabgrass from year to year. See the info on Tupersan in this pub: https://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/tt-43e-crab.pdf


ECN





Thank you for your response.
So, what are you proposing I do now? I'm a bit confused.
I understand that you think I should plant a lawn in the early fall, but what do I do until then?
As of March 25 when I'm writing this, I have a lawn that is greatly overrun by crabgrass. Should I:
1) Apply Tupersan to kill the emerging crabgrass and
2) Apply grass seed (since there isn't much of a lawn now)
3) Then, in early Fall, seed again?
4) When planting this lawn, should it be after a period of completely rehabbing the lawn (killing all vegetation, tilling, adding nutrients, etc, then seeding)?


It would be helpful to us if you would send us a photo of the crabgrass. Crabgrass is an annual and must come up from seed each spring. It is dead and mostly decomposed at this point in the year. We want to insure that you are not battling a different kind of weed grass.

1. If your lawn is mostly crabgrass, then...:
when you use a pre-emergent in spring, you will end up with a lot of bare areas which will quickly be filled in with other weeds, just not crabgrass. You'll need to seed this spring to prevent this. Use Tupersan, and plan to overseed or renovation seed in fall.

2. If your lawn has lots of crabgrass, but you have a reasonable amount (more that 50%) grass, then...:
Use a pre-emergent, which does not need to be Tupersan (see the pre-emergent herbicide pub we recommended above). Overseed in fall if you need to thicken up the turf. You probably will.

Before you sow seed, be sure to get a soil test and apply lime to correct the pH if recommended by the soil test. Also follow fertilizer recommendations.

There is much more that goes into a successful lawn. Mowing height, for instance, if critical. Please study the pub we recommended on general lawn maintenance and seeding.

ECN


Hi,
Attached is a photo I found of the weed. Is it, in fact, crabgrass?
I've had the soil tested. It is 5.4 pH. I've treated it with lime previously, and plan to do it again.
As for the sun/shade issue, the answer is complicated. Half is sunny; half is shady.

The weed in your photo looks like japanese stiltgrass, an invasive weed. See the link from Weeds Gone Wild for more information http://www.nps.gov/plants/alien/fact/mivi1.htm
Japanese Stilt Grass is very invasive and adapts to a wide range of conditions sun or shade. Fighting it may be an ongoing process.
In general your best option for control in a lawn is using a preemergent herbicide at the same time you would apply one for crabgrass control in the spring. Seedlings emerge about the same time as crabgrass. Barricade and Pendulum are the most effective ones for this particular weed out of the many preemergents to choose from. If you use these them, you cannot seed. We do not have research on how effective Tupersan is on stiltgrass.
Keep the area mowed to help prevent the stiltgrass from forming seeds.

Consider lawn renovation late August - early September. Your pH is low. Grass grows best between 6-6.8 pH. See our publication below for site preparation steps and maintenance. You can till in organic matter such as compost and lime and fertilizer recommended from your soil test. Seed with a turf type tall fescue grass seed for part sun to part shade conditions.
http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG102%20Lawn%20Estab...
mh







Thanks.
So -- until August when I renovate the lawn -- I'd like to have a lawn in the meantime. If I apply pre-emergents to kill both crab grass and the stilt grass soon, how long do I need to wait before I can plant grass?

If you apply the above preemergents, you will have to wait 16 weeks before seeding. You will not be able to seed this spring season.
See the attached publication on crabgrass preemergents https://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/tt-43e-crab.pdf
mh

Given your latest guidance, there would be little need to use Tupersan since I won't be planting seed anytime soon.
Two questions:

  1. Is there a pre-emergent that works on both crabgrass and Japanese stilt grass?
  2. After the initial application of the pre-emergent, what herbicide should I use for the remainder of the period until I renovate the lawn in August?
I'm hoping some sort of existing lawn pops up between now and then.
Thanks for all your help.

The preemergents listed above are labeled for crabgrass control and are the most effective for stiltgrass. This is the most up to date research we have.
Otherwise, handpull and mow.
mh

Hi,
The list you sent has more than a dozen herbicides. From your experience, which would be most effective for dealing with these weeds?
Also, what would you suggest as a POST-emergent herbicide to be used later in the Spring?
Thanks

As mentioned above: Barricade and Pendulum. These are product names. The ingredients you are looking for are Pendamenthalin and Prodiamine respectively. Just look for a product that has those ingredients.

We are not allowed to recommend any particular post-emergent herbicide product over another. There are many on the market. Read the label and be sure your lawn's weeds are in the list of weeds it works on.

ECN