Warm, wet weather makes favorable conditions for some southern species. Ramon Leon, assistant professor weed scientist at the University of Florida, talks about a few problem weeds in the south.
What type of weeds are causing the heaviest pressure in your region right now?
During the summer, the weeds that are really causing a lot more problems for golf courses are goosegrass, and it’s all across the state. The problem with goosegrass is it emerges in the spring, but it shows a very aggressive growth in the summertime. We used to have very good control with a combination of MSMA and Sencor, but MSMA was banned in Florida for turfgrass use. So, we lost probably the tool that growers felt more confident would take care of goosegrass as a postemergent control.
How is weather affecting your region for weed pressure?
We have another two species that have caused problems. One was tropical signalgrass, which is a central-southern Florida weed. That’s very difficult to get rid of and it’s a similar scenario to goosegrass. The other one we have a lot of reports on this past year is doveweed. It’s not commonly found in courses, but we’ve had a lot of rain early in the spring and then in the summer. This is a species that likes hot and wet conditions. We’ve received a lot of calls about doveweed popping up in fairways and it’s even worse in home lawns and for the landscaping industry. The problem is, it’s not necessarily annual rainfall accumulation, but it’s very strong rainfall, and it gets very wet when it’s spring, and in early summer those hot conditions make it very, very favorable to doveweed.
We’ve seen it popping up in all these areas, especially if you have some drainage issues and have a lot of intensive rain early in the summer when the temperature starts being 85 degrees.
It’s not necessarily something I think is going to stay a long time or be reoccurring, but if we get more of these phases 3-4 days with a lot of rainfall, that’s the kind of scenario that gets these things going.
Our soils are very sandy, so we get this intensive rain coming in that’s basically going to wash out your pre-emergent herbicide. Then you don’t have enough on the ground to catch those emergents and herbs. Now one of the things we’re recommending is trying to split your pre-emergent herbicide application so you can catch crabgrass early in the season and then go with a second application 45 days later to have enough herbicide on the ground to catch late emergers.
What about weeds like kyllinga and dallisgrass?
Well, kyllinga is found frequently throughout the state, because it’s a plant that is very well-adapted to the irrigation patterns we have on golf courses. It’s frequent light irrigation, and the seeds need that moisture to really get established and germinate. Then, it’s adapted to fairways and even greens, so it’s a very common plant that you’re going to find on golf courses, especially in Florida. However, it’s not considered a major weed because we have herbicides, and they’re very effective at controlling it, especially post-emergent herbicide. Kyllinga is one of the sedge species, it’s frequently found, but not necessarily a major management challenge for superintendents. They might have some issues with another sedge, which is purple nutsedge. That’s a major challenge because the herbicide that will control kyllinga will provide partial control, and that’s it.
But luckily, it’s not as frequently found on golf courses just because it’s not so well-adapted to the mowing heights that we have, which kyllinga handles better.
Dallisgrass is – a few years ago we had a lot more people complaining about it, and I think it also had to do with the loss of MSMA from the turfgrass market. It’s not a predominant plant, but it was found on golf courses. We’re seeing a lot more of them in the roughs, for sure, and a few cases in the transition between the roughs and fairways, especially on low-budget golf courses.
Is there a reason they tend to do well there?
Well, their mowing frequency and their height with the roughs will favor dallisgrass much better than in the fairway. Dallisgrass is kind of like the opposite of kyllinga. Kyllinga is very well-adapted to the short mowing height because it can outgrow the turf very quickly, but it’s not going to do as well in the roughs just because it’s a short plant. Dallisgrass is a bigger plant and can out-compete the Bermuda. It does not handle the short mowing height we have in the fairways. It can survive, but it’s not going to thrive.