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Existing weed control

Posted by GardenAl 7 (My Page) on
Fri, Mar 29, 13 at 21:28

Thanks to those of you who helped me with questions about pre-emergents that are safer for dogs. I applied Amaze preemergent about 2 weeks ago.

My next question is what do you suggest to use to kill the existing weeds? I'm attaching another picture to show the current state of the yard. Again, the conditions are that I want to find the safest, but effective, treatment.

Also, when should I apply this? Do I need to allow some time?

Follow-Up Postings:

RE: Existing weed control

I'm not sure what area you're in, but I definitely recognize that weed. Annual Bluegrass, sometimes referred to by it's scientific name "Poa Annua" is a difficult problem especially in areas with clay soil.

By far the best post-emergent control is made by Bayer, and they know it's the best. Revolver is an amino acid blocker, which kills a wide range of cool-season grasses including both Poa Annua and Poa Trivialis. The great thing about this mode of action is that there is little to no risk of herbicide tolerance/ resistance becoming a problem. The downside is the cost as it is among the most expensive herbicides per 1,000 sqft.

Another choice is a product called Certainty, which also offers Annual Bluegrass control, but usually doesn't perform as well, and has some draw-backs such as the fact that it becomes inert after 3 to 4 days in water, so you have to mix exactly what you need at the time of application. Also, it too is a pricey product as it is fairly new. The major advantage is that it is the best control I've seen for Purple Nutsedge, which is a perennial summer weed.

Personally, I would let the heat take care of the Bluegrass at this point. If you kill it with either product, it will simply turn yellow and sit there until the temperatures climb enough for it to decay. Also, post-emergent herbicide used during Spring Transition is more stressful to the lawn that when the turf is active and can metabolize the herbicide. Spraying during transition often stunts healthy turf.

When you get to Fall, the most trusted product for prevention is Simazine, which is very cheap to use. I have personally done field tests on several others and not seen results that compare. There are a couple of new products I will be trying this year, but they are very concentrated and high priced.
The link shows the results achieved by Simazine in the Fall at the proper rate for Bermuda (3/4 oz per 1,000 sqft).

Here is a link that might be useful: property line with neighbor's annual bluegrass

RE: Existing weed control

Thanks for the response, serenity. The Bayer Revolver sounds like powerful stuff, and it is pricey. I'm wondering how far one 32 oz. bottle would go. I read that 1 oz per 1,000 square feet. My yard is about 15,000 square feet, so that means one bottle would treat the yard twice. How often do I need to apply this? Once a year? Twice?

Also, more importantly for me, is this stuff safe for small dogs? Obviously not at the time I apply it, but will I be able to let them out in the yard within a day of applying?

I am attaching another picture of different snapshots of weeds in the yard. I'm not familiar enough with weeds to identify them, but I do know we have several types. I'm showing this to you in order to give you more insight to what we have.

Thanks again!

RE: Existing weed control

The Revolver has a low toxicity level, so after it dries it is fine to let the dogs out.

Revolver is almost always applied through a handcan or backpack sprayer. The math on this is usually 1 gal per 1,000 sqft, of solution, so 1 oz. per gallon. As for coverage, only apply it to the Annual Bluegrass, which I hope is not covering the entire lawn.

The other weeds are broadleaf, so you have a wide variety of low cost herbicides available. Most broadleaf herbicide control has some form of a phenoxy acid, such as 2-4 D or Mecoprop (MCP or MCPA), with a similar acid Dicamba. This combination of 3 comes through in the trade names as well: Three Way, Trimec, Tri-Power, etc. Most nurseries or your local John Deere Lesco can provide a 1 gallon or 2.5 gallon jug, which would last a long time. The rate is usually 1.1 - 1.5 oz per 1,000 sqft, which again is per gallon through a handcan or backpack.

Unlike many lawn care companies, I choose to spot spray virtually all of my post emergent weed control during Spring. The reason is that post-emergent herbicides can stunt transition and increase the risk of disease activity during transition. During a lawn's normal growth period, most herbicides are metabolized by the grass and have virtually no ill effect, but during transition the grass is more susceptible to damage while the new growth comes out and as the soil temperatures fluctuate with Spring.

As for repeat applications, at the rate of 1 oz (3/4 of an oz is usually effective for Poa). One application is plenty, as it is very effective control. If you do a good job on pre-emergents in the Fall, you will reduce the Poa activity by 80% on average in the following season. So the Revolver would be used again in March, but not to the same extent. Revolver is also used on Dallisgrass and combined with Certainty or Celsius during transition. Dallisgrass is a whole other topic though.

The before and afters on the link below can be seen at the bottom of the page. The one on the left shows weed control as describe for broadleaf weeds and the one on the right shows a lawn full of Bluegrass last season vs. the beginning of this season after two Simazine applications in Fall.

Here is a link that might be useful: before and afters at the bottom of page

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