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?
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:
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
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.
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.