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Treat lawns for summer weeds now

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POSTED: February 13, 2014 3:30 p.m.

It is time to apply the single most cost-effective weed control treatment to our lawns — the winter pre-emerge herbicide treatment.
 The second most cost-effective herbicide treatment is the winter-weed pre-emerge herbicide treatment, which should have been applied in September. This single application can prevent almost 95 percent of the weeds from appearing that otherwise would appear if the treatment was not applied.
It only takes a small amount of herbicide to kill a small, weak, juvenile weed. Wait for a few weeks for that weed to establish itself, and it gets downright ornery about giving up its place in your lawn. This is one of those circumstances when a little herbicide now prevents a lot more herbicide later.
We want to reduce chemical use in the landscape, not just for all the altruistic environmental reasons, but also because the chemistry is getting ever more expensive. The less I have to spend on lawn chemicals, the better.
Most of the weed seeds we worry about in our lawns use soil temperature as the signal for sprouting. The winter weeds sprout when the soil temperature drops below the low 50s. Weed seeds do not all germinate at once or even in the same season. It is common for a single season’s crop of weed seeds to persist in the soil for four years or more. Soil temperature fluctuates a lot. It seesaws up and down with the weather. Every time the temperature seesaws down, a few more weed seeds germinate.
Summer weeds use warming of the soil as a cue to start germinating. The weed seeds sprout when the soil temperature jumps above 50 degrees. Our lawn grasses wait for temperatures to get up to 65 before waking up, so the weeds easily can get a head start over the lawn in the spring. That is one of the reasons a pre-emerge treatment is so important for weed control.
Our calendar average for having our summer pre-emerge down is Valentine’s Day, but this year that is not quick enough. The warming trend after the winter system that crippled Atlanta was so abrupt (remember that 80 degrees we had Monday last?) that soil temperatures spiked right past 50 degrees and even past 60 degrees. If you plan to get a pre-emerge treatment down for summer weeds, the time to do it is now.
A word about herbicides. On St. Augustine, professional turf managers have 19 recommended pre-emerge herbicide mixes from which to choose. They also have 19 recommended pre-emerge herbicide mixes to choose from for centipede as well. Most, but not all, work on both lawn turfs. Homeowners have a more limited menu of six chemicals from which to choose. All can be used safely either on St. Augustine or centipede.
To avoid advertising a specific brand, I list here the common chemical name of the active ingredient: oryzalin, benefin, benefin plus oryzalin, benefin plus trifluralin, pendimethalin, dithiopyr and atrazine.
Atrazine has been popular on St. Augustine. Atrazine also can be used on centipede lawns as a pre-emerge herbicide when the lawn turf is dormant. Atrazine also can be used on centipede as a post-emerge herbicide in the middle of summer. However, do not apply atrazine to centipede during green-up in the spring unless you really want an orange lawn.
Now get to it. Punxsutawney Phil may not have seen his shadow, but Gen. Beauregard Lee definitely saw his. Springs a comin,’ and times a wastin’!

Gardner lives in Keller and is the UGA extension agent for Glynn County, serving South Bryan.

 

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