Poa Annua or Annual Bluegrass is a ugly, difficult to control, winter annual weed in your Atlanta dormant bermuda lawn. This weed spreads millions for seeds each year that can infest a lawn if not treated. That being said, lawn care companies for years could never get good control of this weed no matter what we did, because the weed controls available did next to nothing to control them. Over the past 10 years weed controls have improved and we typically get 6 months worth of pre-emergent control. Now you might say that is pretty good, right?
Well, it is excellent control, considering most pre-emergent treatments last about 4 months at best. Lawncare companies in the south apply a pre-emergent in the fall to control the POA, since it germinates in September/October depending on when the soil reaches 55 degrees. Once the soil temps drop this bad boy starts to germinate and it can get ugly fast if you don't apply a pre-emergent.
If the pre-emergent is applied to prevent the POA, why do I see it in my yard in the spring? There are many factors that cause to happen.
First, we usually see POA show up about the second week of March. Remember the 6 months we talked about earlier? Depending on the time frame of your application, March is about 6 months after it was applied. So pre-emergent products breakdown from the rain, sun, traffic, and breakdown even faster in shaded areas where there isn't much grass to hold the pre-emergent a soil level. Also, scalping your yard too early causes the lawn too be thin and contributes to pre-emergent breakdown. Scalping Your Bermuda Here in the Atlanta area, we have been having abnormally large amounts of rain the past few years during the fall, winter, and early spring. In, 2020 for example in the first 3 months of the year, we received half of a full years rainfall, that is a lot of rain in a short period of time. That caused a lot of pre-emergent breakdown and POA, so much so that the manufacturer of the pre-emergent came to Georgia to research why we had such a bad breakdown. In some causes we saw it breakdown by January.
Second, the pre-emergent is applied and needs to be watered within a few days of application or it breaks down and loses effectiveness. So, if we didn't get rain or you didn't water, its not going to work too well. I live on an 1 1/2 acres with no irrigation, I apply my pre-emergent when its going to rain or even in the rain. Pre-emergent typically needs an inch of rain or water to get it to the soil level. Most rainfall is 1/2 to 1 inch so, don't worry if we get rain after it is applied.
Third, pre-emergent creates a barrier on the top of the soil by binding with the soil and preventing weeds for coming up. Therefore, it stops seeds that would germinate in the soil from growing. It however, does not stop the seeds that land on top of the barrier. On windy days in the late winter and early spring, the seeds can blow from other lawns and or come in with your mowing service and grow with no prevention. This is when a lawn care company has to treat the POA with a post emergent. Now remember we said it is difficult to control? There are very few post emergent weed controls that will control the POA, really 1 that is labeled for residential use and has good results in my opinion. Once the POA is treated it takes up to 6 weeks to control the POA. Why? The POA is so close in its genetic makeup to the good grasses that it works slowly to not damage the grass you are trying to keep. Also, depending on air temperature, if it is cold the weed control works much slower because the POA has closed its pours to keep in moisture and will not ingest the herbicide.
Now based on the facts, if you have some POA in your lawn in March, your service results are not that bad, in fact the results are great. As a homeowner you don't like the POA in your lawn, I understand completely, but if was easy to control like most broadleaf weeds, I would not be writing this article. Oh, remember, I mentioned soil temperatures for germination? When the soil temperatures go above 55 degrees and continues to warm, the POA dies naturally. Be patient it will come under control one way or another and the longer you treat your lawn properly the less you will have year after year.
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