[QUOTE=goldenrow;8208974]
Glyphosate products (RoundUp/Touchdown/Cornerstone/Abundit/GlyStar/etc) will only kill emerged weeds. In order to prevent new weeds from germinating or emerging, you will need to ask your ag supplier for a residual herbicide (use the word “residual” or “pre-emerge” - that’s the lingo to say you don’t want any more weeds after you kill the ones you have).
Even the best residual herbicide has a point where moisture and sunlight breaks down the particles in pieces (carbon, hydrogen, nitrogen, etc) that no longer kill weeds. You WILL have to reapply multiple times in a season - weather will determine how many times.
The problem with most residual herbicides is that they will be VERY expensive to purchase a whole container. (Example: Sharpen is $775 per gallon - but you only use 1 liquid ounce per acre = $6.05 per 43,560 square feet - my outdoor arena is only 30,000 ft2.) It is against the law to sell partial containers, unless it is custom applied.
So it may be worth it to ask if they have a small commercial applicator and are willing to spray it for you.
If not, use a mix of 2,4-D and glyphosate. Both are safe for horses to be around as soon as the spray is dry. I wouldn’t necessarily let them eat the sprayed weeds in bulk, but if one grabbed a nibble, they will not be harmed. You may have to spray a time of two more than if you can use a residual herbicide, but it’s a quick process once you do all the math for how much you need.
As always - feel free to PM me if you have any ag chemical questions![/QUOTE]
The info on pre-emergents is really helpful, thanks golden! Is there any possible value in trying to use salt to prevent new weeds (actually my main problem is just plain grass)? I have been at barns that used rock salt to prevent freezing in the winter, and my horse suffered no ill effects. I do know that it would dissolve and wash out with rain though, so I’m thinking the amount of salt I would have to use and the frequency with which I would have to reapply it would probably make this a no-go. Any thoughts?