Turf - Controlling Zoysiagrass in Cool Season Turf

I was recently asked about controlling Zoysiagrass in cool season turf. Here are some thoughts.

Zoysiagrass is a warm season grass that goes dormant from mid-fall through mid-spring. Although some homeowners like the grass because of its fine texture and ability to stay green in the middle of summer heat, others hate having the brown look for more than half the year.

Zoysiagrass spreads mainly by underground rhizomes and above ground stolons. This means it produces stems that run on the surface and just below the surface. As such, it can easily invade flower beds, landscape beds, and neighboring lawns. Although zoysiagrass can produce seed, many of the varieties that were planted in the past do not seed much, if at all. Seed should not be the major way that it invades but can be a secondary mechanism in some cases.

Keeping zoysiagrass from invading an area is difficult. Barriers to the underground rhizomes could help. Bury a 12" barrier such as thick plastic, fibergrass, or metal, slanting the barrier toward the area being invaded with another 6" out of the ground. This will keep the underground rhizomes from invading and you will be able to see the above ground stolons as they try to grow over the barrier so you can control them. To control any growing over the barrier, routinely use a sprayer or wick applicator and apply glyphosate herbicide (Roundup and many other brands) on the zoysiagrass growing over the barrier. Mowing will break up the zoysiagrass into smaller pieces that could potentially root and spread the grass even more. If you mow, you need to collect the clippings.

If an area has already been invaded, bite the bullet and use glyphosate (Roundup or equivalent) herbicide and spray the area once the zoysia has greened up in the late spring. This will kill everything but does not leave a residual. Do this every 3 weeks until you see no more zoysiagrass coming back up. You can then reseed or sod in the late summer with the desired turfgrass. You will have a dead area all summer but it is the only way to effectively eradicate it. Digging does not do a very good job, close mowing will not kill it, and there are no good selective herbicides that will kill Zoysiagrass and not the desired grass. There are some reports in the literature that higher rates of MSMA, fenoxaprop, or fluazifop may cause some suppression of Zoysia. Note that MSMA has been routinely used in zoysia in the past as a herbicide so don't expect much control. Of the three, fenoxaprop (Acclaim) will have the most effect on zoysiagrass.

Gordon Johnson, Extension Agriculture Agent, UD, Kent County