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I would like to thicken some Roundup to form a drip-free paint for targeting weeds in groundcover beds. If I use Thick-It starch based food thickener, will I get the result I want? I would be watering down the Roundup 4-5 times normal, because of how thick it would go on. I could also add a wetting agent if it would help maximize contact. Does anyone see any problems with this idea?

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    seems like a good idea, if you could end up using less in the long run... you would probably want to experiment, if you go too thick you won't be able to apply it ... there is some potential of the glyphosate forming a conjugate with the starch, or xanthan gum or whatever carbohydrate thickener you use, which would make the glyphosate less available... I don't know that it will happen, and it may be one of those things that happens slowly, or only at high temperatures ... – Grady Player Jun 7 '14 at 0:21
  • This is a ready make product a bit expensive, but easy to use lovethegarden.com/products/weed-control/roundup-gel – Ian Ringrose Jun 26 '18 at 15:30
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I don't know if it works with food thickener, but it does work with wallpaper paste - mix the wallpaper paste powder with straight Round Up or glyphosate only, no water (unless you're using a glyphosate concentrate which needs to be diluted), to the consistency you want. Adding a wetting agent might help too if you're using plain glyphosate, (in the UK, a squirt of washing up liquid is the commonest one used) but isn't necessary if it's Round up - it already has other ingredients that do this job, which incidentally render it more harmful to the environment. What also helps with tough leaved weeds is to lightly bruise or crush the leaves before applying.

UPDATE IN RESPONSE TO COMMENTS:

J Musser;

  1. the wallpaper paste is likely somewhat less dangerous in the environment than Round Up itself, if you're going to use Round up, but the quantity is small anyway

  2. I'm not sure what you're saying re dilution - if you want a thick mixture to paint onto leaves, why would you want to add water as well, if you don't have to - it just dilutes the glyphosate. As I've said, the usual course is to mix standard glyphosate directly with a bit of wallpaper paste powder till its the right consistency.

UPDATE 2: J. Musser - you've asked about toxicity of wallpaper paste in the outdoor environment. The type I'm talking about (traditional, old fashioned wall paper paste powder that you mix yourself, if you can find it) is fine to use, since the ingredients are only 3-10% solids and these comprise wheat paste, cellulose, potato, tapioca or other starches. It's the Round Up you want to worry about - that binds to soil particles and can still be present in the soil up to 200 days later, though more usually about 3 months.

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  • Unfortunately some weeds, even if you crush the leaves first, are resistant to Roundup. Horsetails or equisetum are one of these. Now I just pull them. – kevinskio Jun 7 '14 at 16:57
  • @kevinsky sometimes pulling will do lots of damage to the groundcover, also the weeds in question will come back from underground runners. – J. Musser Jun 7 '14 at 18:58
  • @Bamboo What's wrong with watering it down? – J. Musser Jun 8 '14 at 2:11
  • @jmusser - watering down means the glyphosate solution is weakened, though if you're using a glyphosate concentrate which should be diluted before use anyway, that's a different case - normal dilution rates apply, and that is then mixed with dry wallpaper paste powder. – Bamboo Jun 8 '14 at 11:31
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    @kevinsky, I have found that Round Up Pro works on Horsetails, if you give the Horsetails a light brushing first. – Ian Ringrose Jul 5 '14 at 15:47
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As a followup, I tried my idea, and it worked quite well. The reason for this post is to point out that you can get away with .75% glyphosate on most weeds. I also used some pre-mixed glufosinate on some Canada thistles, and applied similarly, with success. Also, @Bamboo's idea, using wall paper paste, works well too.

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