Caring for your Warm-Season Lawn During Fall

During the summer months, warm-season lawn managers typically don’t have a lot to worry about. Keeping up with all the mowing can often be the most challenging aspect of managing warm-season lawns during the summer, especially if rain is plentiful. Maybe some of you managing warm-season lawns in the transition zone have enjoyed keeping an eye on your neighbor managing a cool-season lawn, trying to keep up with irrigation and fungicide applications during the summer months. You and your cool-season neighbor are both nearing the end of a long, hot summer and this must mean all your work is done for the season, right? Think again. 

Thankfully, you won’t be needing to do any core aerating or thatch removal, as your lawn won’t have enough time to heal up properly prior to winter dormancy. But, you will still need to continue to mow (hopefully, less frequently) and get some herbicide applications out prior to winter. So, the work isn’t totally done for the season but none of it is dreadful. Because all warm-season grasses behave differently, a “one size fits all” plan for fall management isn’t always the best option. Take into consideration, your location, grass type, and weather patterns, and adjust the following recommendations to fit your specific situation. 

Mowing your warm-season lawn in the Fall 

Mowing will still continue until the first frost date. Sometime around early- to mid-September, raise your mowing height by half an inch for increased protection from winterkill. This can help insulate the crowns of your grass plants. The crowns are the main growing points for your grass, so ensuring their survival is paramount. Continue mowing until you’ve noticed that your grass has stopped growing, sometime around the first hard frost. The 1/3rd rule still applies during the fall unless you’re planning on overseeding your lawn with cool-season grass for some winter color. If that’s your plan, make sure to do your last mow prior to seeding as low as your mower will go. Collect or somehow remove all of those clippings to ensure that your seed makes as much “seed-to-soil” contact as possible. 

How much water does my grass need? 

Depending on your weather patterns during the fall, supplemental irrigation may or may not be called for. If it’s been dry for the last part of the summer and early fall, with no rain in sight, some supplemental irrigation may help bridge the gap until your lawn deems it time to go to sleep for the winter. If you can tell temperatures are on a meaningful downswing and your day lengths are noticeably shorter, holding off on the irrigation will not hurt you. In fact, it may help ease your lawn into winter dormancy a little earlier than usual to just avoid irrigating and let Mother Nature do her thing. As long as you don’t allow your soil to just become a complete crusted-over mess of desiccated turf, rely on your own judgment for irrigating.

What is the best fertilizer to use for my warm-season lawn in the fall? 

Less is more in the fall. It’s probably best to put away the nitrogen fertilizers after about mid-September. Avoid heavy applications of nitrogen this late in the season. Heavy nitrogen in the fall on bermudagrass specifically, is associated with increased spring dead spot incidence. Select a fertilizer with no or low nitrogen and high potassium like SLS 0-0-25. Aim to make this application a few weeks before your first frost date.

The Best Weed Control in Fall

The fall is a great time to control both perennial weeds, along with preventing winter annual weeds. Weeds like dandelion and thistles will be storing nutrients in their large underground storage structures for overwintering and subsequent growth next spring. Applying a systemic herbicide in the fall is effective for controlling these weeds, as the herbicide will be translocated to the storage structures, ultimately resulting in plant death.

Winter annual weeds can be controlled with one or two properly-timed preemergence herbicide applications. Aim to get your herbicides out before soil temps drop below 70 F. Remember Poa germination occurs at soil temps of 70 F in the fall. This means you want your preemergence herbicide out in the soil ready for uptake prior to Poa or other winter annual weeds germinating. You can try to increase your window of control by splitting up your application into two half-rate applications, 2-3 weeks apart. So the idea would be to get some preemerge down with plenty of time prior to soil dropping to 70 F. This will help to control the early germinators. You can then come back 2-3 weeks later with your second half-rate application to prevent the growth of others that weren’t ready to germinate when you put down your initial application.     

How to Control Lawn Disease in Warm-season lawns?

For bermudagrass lawns and some zoysiagrass cultivars, spring dead spot can result in unsightly patches of dead turf that fails to green up in the spring. Spring dead spot is unpredictable and should normally only be treated if it has been a problem in the past. Preventative spring dead spot fungicide applications should be applied after soils drop below 80 F but above 60 F during early fall. Adequate control may require two applications in the fall. Water in heavily to move the fungicide into the root zone. Avoid heavy late-season nitrogen fertilization as this can increase disease severity. A good thatch reduction program in the summertime can also help limit disease severity. 

Large patch has multiple names, you may know it as warm-season brown patch or just as Rhizoctonia. Regardless, this disease can be nasty in the shoulder seasons of the fall and spring on zoysiagrass and St. Augustinegrass. Bermudagrass is susceptible but rarely sustains lasting damage. Large patch is caused by a different strain of the same fungus that was giving your neighbor with tall fescue fits all summer (brown patch - Rhizoctonia solani). You typically want to target preventative fungicide applications around soil temperatures of 70 F in the fall. For St. Augustinegrass and centipedegrass these applications can be made even earlier than that. Again make sure to heavily water in your fungicide application.