Pair strong maintenance with herbicide to keep goosegrass out.
Goosegrass is one of turf’s most resilient weeds, taking advantage of any weak spot in the canopy. Shawn Askew, extension specialist and associate professor for Virginia Tech, talks about how to keep it from making its move.
How do you recognize goosegrass, and where should we look for it?
The typical expectation for goosegrass is that it’s going to have very flat stems. Its tillers lay flat to the ground, and the center of the plant’s going to have a whitish to silvery appearance to it. A lot of people refer to it as silver crabgrass – that’s a common alternate name. But for most people in the U.S., what we’re dealing with when we’re looking at an Eleusine plant, it’s going to be Eleusine indica or goosegrass. It has a folded vernation, which is a good ID characteristic, meaning the newest leaf emerging from the center of a tiller will be folded rather than rolled up like a corn plant. It also has a very large membrane ligule. Those are pretty common ID characteristics: the flat growth of the tillers, the folded-in-the-bud vernation and the large membrane. The seedhead is three-parted and looks like a goose’s foot. It loves compacted areas or any area where it’s free from the competition of other plants.
What type of soil is it going to do well in?
It’s a chicken-or-egg situation. Research that’s been done on goosegrass suggests that you will most often find it in openings in the turf canopy and definitely find it in areas where there is extreme compaction. We’re talking walkways, or paths that are beaten down to the consistency of concrete. It’s known for literally growing in cracks in concrete. Those are very hot habitats, and goosegrass is a heat-loving plant. But that’s not to say that a beautiful, lush garden soil that’s in no way compacted won’t produce large and happy goosegrass. But you won’t find it as readily if it has to compete with other plants.
It will germinate a little later in the season than crabgrass, and it tends to have a little more continuous germination into the hotter period of the year. At hotter soil temperatures, it’ll continue to germinate. If you want it to grow, you need to have a lot of wet followed by a lot of dry, and a lot of light followed by no light. In other words, you need to alter wetting patterns and you need to have diurnal light exposure. That exactly mimics a turf canopy opening where you rapidly dry the surface of the soil and then get rewetting, and then dry very rapidly again. Goosegrass likes that. It’s different than a dense turf canopy where things are generally going to stay uniform and slowly dry out over time rather than have these huge fluctuations and drying period.
That sounds like a sparse, irrigated turf.
Exactly. And late season is where goosegrass comes into its own, so germination will increase in those situations. If you think about an area where the turf is being watered, if you have a halfway decent turf canopy, the fluctuation and wetness is going to be minimal. But if you have a bare spot, it’s going to be huge. It’s going to go from really wet to bone dry very quickly, and that will stimulate goosegrass to germinate.
One point to make is that herbicides used as a pre-emergent for goosegrass control will never be completely effective in an area of turf that’s devoid of cover. If you have a lot of openings from spring dead spot or some other disease, or maybe some really beat-down turf on the side because of traffic that creates openings in the turf canopy, you can’t protect those areas from goosegrass with a pre-emergent herbicide like you can others. Or, said another way, a pre-emergent will never last nearly as long in the face of those openings as they will in good, uniform, dense turf.
The area that you’re going to see more goosegrass in a lawn setting is what I call the no man’s land between the street curb and the sidewalk, that little sliver of grass that the architects in the subdivision will leave. There’s just no good way to manage it. It’s too small to manage for typical operators, plus most LCOs with increasing regulatory restrictions are very worried about putting granules on the hardscapes. On top of that, you have extreme heat, you have solar radiation bouncing off the asphalt – goosegrass loves that. Then, you also have water infiltration, because you can imagine the type of soil the average contractor is going to put back into that spot. I get a lot of calls about that strip of land.
What preventive products should we be looking at?
The best product to protect one’s turf from goosegrass is going to be oxadiazon, which is going to be the gold standard for long, residual goosegrass control. My second-best is prodiamine. Prodiamine can do a great job at preventing goosegrass.
But there’s one problem. We apply relative to when crabgrass germinates, and it starts germinating a couple weeks to a month later. So when it germinates, we’ve already lost our most potent first four weeks of activity for that herbicide. Your highest AI load is in that first month – you don’t even get to challenge your goosegrass population with that first month of AI. The way to combat that is repeat applications. You can come out with your initial app for your true pre-emerge, then follow up about a month to two months later with a follow-up application that can give you a little bit better extension. Products that contain surflan or trifluralin are not very effective on this grass. Changing your ingredient to an oxadiazon or prodiamine product would be a smart move from a preventive standpoint.
Post-emerge herbicides are a big problem across the board. The number one product used to kill crabgrass over the top is quinclorac, and it’s about as effective as water in killing goosegrass. In Bermudagrass, we don’t really have effective post-emerge options anymore. The primary ones would be used on tiny seedlings. You can use foramsulfuron or sulfentrazone, which we use to target sedges. We do have a newcomer to the cool season world that is the proverbial silver bullet, and that’s topramezone. That’s the most potent single AI that will kill goosegrass at any stage, depending on the rate. The other products I haven’t mentioned for cool season would be mesotrione, which has activity on goosegrass, but it takes two applications, and it will only control active seedlings, like I mentioned. It’s really only warm season turf that we have these limitations. In cool season turf, we can up the rate of fenoxaprop-p-ethyl to where it needs to be, where we can’t do that in Bermuda. In the warm season we would have extremely expensive products that only work on tiny seedlings, and are going to be inconsistent. In warm season turf, you have to work on your turf cultural practices to maintain a solid canopy and you have to integrate pre-emerge herbicides such as oxadiazone to get good residual on the goosegrass.
A good aerification program will keep things moving. A lot of people will ask, “Well, I’m going out with my pre-emerge now because crabgrass is about to start germinating, but I’m not going to aerate until about three weeks from now. Aren’t I going to destroy my herbicide barrier?” and the answer is no, this is not an idea situation, but you’re not going to destroy your herbicide barrier. Herbicides can move slightly laterally, and they can come in and fill back in the barrier, especially when it occurs fairly soon after the herbicide application. So my argument has always been that the negative impact on your herbicide barrier due to aeration is less than the negative impact on your turf due to not aerating. Your turf kills more goosegrass than the herbicide. It’s hard to measure, but it’s out there doing it every day, before you wake up and after you go to bed. Therefore, to preserve its ability to fight goosegrass, you need to alleviate the compaction, give those roots some oxygen and give it room to grow.
Goosegrass is an extremely robust plant from a genetic standpoint. It’s developed resistance to all the modes of action against everything that’s been developed to throw at it. So if you deal with a lot of goosegrass, incorporating a resistance management program would be advised.