SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
Issue link: https://read.dmtmag.com/i/591732
50 SportsTurf | November 2015 www.sportsturfonline.com We are about to overseed, is it too late to aerify? I want to control some summer weeds, is it too late to spray? Our tem- peratures have dropped below 55 at night, is it too late to overseed? T wo months ago I wrote an article about spraying post-emergence herbicide on crabgrass after a field manager had waited too late to get his preemergence out. I do not want my comments to be taken as a criticism, but it seems that question was the beginning of a number of "is it too late" questions I received in the past 6 weeks [editor's note: mid-Aug through Sept]. I always heard that timeliness is a virtue. Ok, maybe that is taking it a bit too far, but initiating some turfgrass cultural practices late can strongly influence the outcome. Since we do not always know what Mother Nature has in store for us, we do not always know the best time to do everything. So, we tend to use weather cues and schedule based on previous experiences. But what happens when we are late? For instance, let's take the first ques- tion—aerification before overseeding. Generally, textbook instruction says to aerify bermudagrass fields 4-6 weeks before overseeding to alleviate soil com- paction. Coring is performed that far in advance of the overseeding to allow coring holes to heal over, therefore preventing a speckled growth pattern of the ryegrass. The overseed grass will grow more rapid and greener in and around core holes than between them. Of course when circumstances prevent one from following the textbook's pre- scribed timing, then what? Start by asking yourself if the chance of having speckled turf is worth the known benefit of reduced compaction? That thought process puts safety over aesthetics. Perhaps your soil is not overly compacted so that the ryegrass can be planted without aerification and then once it is well established, the field can be aerified. When the field will be used may influence the decision; in this case the speckled growth pattern will eventually even out. If a late aeration is the only time your field will be aerified for the year, then you may want to throw caution in the wind and go for it. So, there are many factors to consider. The second question also has variables to consider. As was mentioned in my previous "Q&A" on crabgrass, the cool temperatures can dramatically reduce the growth of summer annual weeds. In many cases a turf manager is just as well off not spraying and letting Mother Nature natu- rally take out the weed. This is especially the case if the weed pressure is fairly light and fall is rapidly approaching. If the weed pressure is very high and/or there is amble warm weather forecast for bermudagrass to fill the voids from dead weeds, then spraying out the weeds may be the best decision. Just keep in mind that by the time the herbicide is effective at killing the weed, the growing conditions may not be favorable for bermudagrass growth. A field manager should also be aware of residual herbicide activity if they are going to follow spraying with overseeding. In some cases several weeks must pass before seed will germinate following the herbicide applica- tion. The last question relates directly with overseeding. I get this question dozens of times each fall from homeowners and sports turf managers. In North Carolina we often get a few cool snaps then it warms back up. People think about seeding dur- ing these early cool snaps but by the time they get everything ready it is back in the 80s during the day so they decide to put it off. What they may not realize is that the soil temperatures are continuing to drop because the nighttime temperatures are not getting as high and the days are getting shorter. This can go on for weeks or even months. Then a hard cold front comes through and the days do not warm up so much. Then there is concern that they have waited too late. In this case, textbook instruction sug- gest managers overseed when daytime temperatures in early fall are consistently in the 70s and nighttime lows are usually above 50. Most of our cool-season grass species germinate best with soil tempera- tures between 50 and 65 degrees. Seed too late and cold weather may prevent suffi- cient establishment. So, unlike the previous two questions, this one has an outcome that is largely weather dependent. One never knows if temperatures will warm back up or stay cool. Generally in fall, there will always be a few warm days that can get seed germi- nated, but what is not known is how long it will last. Ryegrass seedlings are tough, but put a lot of traffic on them and they may not be tough enough to see maturity. So to answer this question about late seeding, I usually suggest the person to consider the alternative—a dormant field. If a dormant field is not acceptable, then one should get to seeding and hope Mother Nature is good to you. ■ ST TOO LATE? Q&A with Dr. Grady Miller Questions? Send them to Grady Miller at North Carolina State University, Box 7620, Raleigh, NC 27695-7620, or email grady_miller@ncsu.edu Or, send your question to Pamela Sherratt at 202 Kottman Hall, 2001 Coffey Road, Columbus, OH 43210 or sherratt.1@osu.edu Professor, North Carolina State University Most of our cool-season grass species germinate best with soil temperatures between 50 and 65 degrees. Seed too late and cold weather may prevent sufficient establishment.