Question of the Week: August 12, 2021
“I want a St. Augustine lawn, but bermuda keeps invading. What can I do to help the St. Augustine crowd out the bermuda?”
Given ideal growing conditions, St. Augustine is the dominant lawngrass. It will crowd out bermuda, zoysia, buffalograss – every turfgrass except dallisgrass and nutsedge.
The problem is that we often do not have ideal growing conditions. Pest problems that are rather specific to St. Augustine such as take all root rot in April and May and chinch bugs and gray leaf spot in summer can weaken it severely allowing bermuda and weeds to invade.
The fungicide Azoxystrobin will help keep TARR and gray leaf spot in check. Using a high-quality, all-nitrogen lawn food (upwards of half of the nitrogen in slow-release form), and applying it in mid-April, early June and early September will help avoid the diseases.
Chinch bugs are easily controlled once you learn to identify their early symptoms. That leaves brown patch in the fall as the only other issue, and it can also be controlled with Azoxystrobin. Plus, brown patch isn’t as life-threatening to the St. Augustine.
Honestly, when bermuda invades St. Augustine, it’s most often because people haven’t watered their St. Augustine often or deeply enough.
So those are ways to get St. Augustine to overtake bermuda. The real problem comes in getting bermuda to overtake St. Augustine if the latter is invading from some adjacent space. We used to be able to call on the herbicide MSMA to do that job for us. It would kill the St. Augustine without killing bermuda, but MSMA is no longer available.
The only options now are to install some type of mechanical barrier such as edging between the two properties and then use an edger to maintain the boundary, or to build an actual shrub bed or flowerbed to separate them.
Or you can carefully trace the St. Augustine runners with a fine spray of glyphosate-only herbicide. Yes, it will kill bermuda beside the St. Augustine, but if you use a precise spray nozzle under minimal pressure you’ll be able to keep the adjacent damage to a minimum if you spray just as the invasion begins. Unfortunately, with MSMA gone, those are the only remaining options available to consumers.