My dallisgrass invasion drove me to using roundup on my grass (spot treating) this last summer. I applied it not long before I left on vacation. I forgot to tell my waterer and the guy I hired to cut my lawn. They were both afraid they had done something to kill my lawn :) It did look pretty funny, like my lawn had leprosy.

If your carpetgrass is anything like my dallisgrass, I'm betting the only non-chem method is digging it out.

I thought this was interesting...and helpful for a few, maybe.

Here is a link that might be useful: Lawn Weed ID

Justin,

Carpetgrass is a common name used for several different kinds of grasses in different areas, some of which are desirable and others that are common weeds. It is hard to know how to reply to your question without knowing exactly which carpetgrass you're referring to. I'll assume you're talking about the fairly broadleaved weedy one common in sandy acidic soils that puts up seedheads similar in appearance to those of crabgrass.

Using corn meal as a pre-emergent at the time soil temperatures reach the right range for germination might prevent seeds which germinate in spring from growing (it does not actually prevent germination, but prevents cell growth so that newly germinated seeds cannot grow), but wouldn't hurt existing plants since carpetgrass is a perennial grass. In fact, corn gluten meal also is an organic fertilizer, so while it is keeping the new seeds from sprouting, it also is feeding the existing plants. Corn gluten meal as a pre-emergent is only effective for a few weeks, so you'd have to reapply it as long as soil temps are in the right range for seed germination.

Do you know the pH of your soil? I hate to advocate messing with soil pH in a portion of the area if the pH doesn't need to be changed over the larger area for some reason. I think you'd have to raise your soil pH to at least 7.5 in order to kill the carpetgrass, and I assume you'd have to do that during the growing season when the grass is green and actively growing.

There are several old folk remedies for removing undesirable weedy carpetgrass plants but I hesitate to suggest any of them, having never tried them here. (Carpetgrass won't grow in my highly alkaline soil.)

Some people spray the carpet grass with horticultural vinegar. Others spray it with a saltwater spray because the carpetgrass is not salt-tolerant, while bermuda grass generally is salt-tolerant. Others apply borax (you can use the borax sold in boxes on the laundry detergent/soap aisle). If I was going to try one of those, I'd wait until hot weather because herbicides are most effective in warm to hot temperatures. Also, I'd test a small area first to see if (a) the product I wanted to use was effective at killing the carpet grass, and (b) to see if it also killed the bermuda grass. I'd wait a few days after the test to see how the area responded. If I was happy with how it worked, I'd use it over the entire area where carpetgrass is a problem.

As long as there is a low moist end of the yard, you may have continual carpet grass problems since it thrives in low, wet areas. Is is the kind of low spot where you can add some soil to raise the level of that area? That might help since carpetgrass thrives in low areas that hold moisture and stay damp. By the same token, if you could improve the drainage in that area (say, by aeration) so the soil would drain better, that might correct the problem. Fixing the soil is the best long-term solution so that you don't have to deal with the same issue every year.

Generally, carpetgrass needs more moisture than bermuda grass needs. So, one way to kill it is to starve it of water by not watering, especially during hot, dry weather. Withholding the water generally will not hurt the bermuda grass which is very drought tolerant, but could kill the carpetgrass. Once it dies, you need to rake it out, scrape it out, etc. and remove it. It is perennial so if you leave any live roots behind, it likely will resprout.

Once you get rid of the carpetgrass, work to strengthen and improve your stand of bermuda grass. If not, you'll likely have a recurring problem with carpetgrass year after year. It is one of the few grasses that, with adequate moisture, can outcompete bermuda grass in some conditions.

There also are some organic herbicides on the market, but I've never tried any of them on carpetgrass.

Good luck,

Dawn

I live in south Florida and have Floratam St Augustine. Good luck on pulling out carpet grass. I thought I killed all of it with a double application of herbicide and replaced the areas with sod at $1400. Well after about 6 months, the carpet grass came back due to some very small patches I did not see. I read on another forum that borax would kill it and it works like a charm while not killing St. Augustine. I apply the borax to the carpet grass while the it wet and let it sit on the carpetgrass for a few days before rain or watering. But borax is $4 to 5 a box and expensive since I have bought about 40 boxes over the last 2 years. So, I am going to try limestone since I believe borax raises the ph as well. I tried salt water but it had no effect.