Crack down on crabgrass

Crack down on crabgrass

Crowd out the weed by keeping turf strong and repairing problem areas.

February 27, 2014

When turf suffers under a tough winter, crabgrass takes advantage of the damage. Dr. John Street, associate professor of horticulture and crop science at The Ohio State University, talks about how to keep it from even getting started.

What does the crabgrass pressure look like this season?

I think it’ll probably be similar to typical years. If there’s a significant amount of winter damage due to snow mold or other issues, it could be a problem. Since it’s been a more severe winter than normal, some places where it’s colder and they’ve had tall fescue that might die out with temperatures below -20 - normally these are things that the grass will recover from on its own, but it’s harder when there’s snow mold pressure. You usually don’t see people have to reestablish turf because of a cold winter, but what you do see is some holes in the lawn by that damage. The question is whether or not the cool-season turf you want will fill in before the crabgrass starts germinating. If it doesn’t, you’ve got an increased opportunity for that pressure.

How would you fight crabgrass this year, then?

It’s all in the standard practices that encourage cool-season turf, so proper fertilization and irrigation will help. But it’s not going to be something they did wrong. It’s going to be more about whether there are holes in the turf caused by winter damage. Seedling turf is not going to outcompete germinating crabgrass. Really, in those areas, the best thing is going to be using a pre-emergent herbicide, which in most cases is not going to allow you to do any overseeding, and you’re just going to wait for the mature turf to fill in. There are a couple products you can use on those big bare areas, but the main thing is to asses those areas where you could potentially have more crabgrass because of something that happened to the turf. Look for both damaged turf and dead spots. The thing that will control the germination is just how much cover there is. Anything that will leave a hole in the turf is what they’re going to want to pay attention to.

What should be done once it shows up?

I really prefer that it doesn’t show up at all, but the post-emergent products can be good if you get the grass while it’s young. Most of the time, the pre-emergent products are the better option. The problem with spot treating with post-emergent is that crabgrass is still germinating until July, so that’s going to kill the crabgrass that’s there on that day, but more is going to germinate on that spot. Really, the better option is to put down a pre-emerge on those areas that are suspect. There are also some newer herbicide combinations out there that are both pre- and post-emergent, or you can tank-mix it yourself.

My point is that once the crabgrass is there, going in with a post-emergent means you should plan on going back in a couple of times unless you’re using a pre-and post-emergent combination.