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Using Herbicide in Pastures

I did not see this in your archives...Is spraying weeds in your pasture with an herbicide like Weedmaster toxic to horses? 

The most informative article that I've read is Weed and brush control with herbicides or mowing at www.noble.org But, is it safe???  My mare came in colicking after I followed directions for fertilizing and spraying :( Possibly it was a higher nitrate concentrate in the clover after spraying!?

Thank you for any additional information you may have,


Hi Lori! Your mare MIGHT have been reacting to the herbicide itself, but it's more likely that she may have been reacting to something she ate... that she might possibly not have eaten without the herbicide!

Most manufacturers provide information and instructions about the safe use of their products. According to BASF, the company that manufactures the herbicide "Weedmaster," there is no need to wait after spraying before horses out into the pasture again. I disagree, but my reservations have NOTHING to do with the quality of the product.

Just in case you haven't already looked at the BASF web site, here is a link to their product information for Weedmaster:


Roundup is another very good herbicide, and according to the instructions on the bottle, you could just let it dry and turn the horses out again immediately, but I don't do that. I would recommend that if you use ANY herbicide on the weeds in your pastures, you wait a week or so before turning your horses back out. I'm conservative because there are other factors to take into account.

I'm perfectly willing to believe that the herbicides themselves may be harmless to horses, but alas, it's not just a question of whether the herbicides present a risk. The biggest problem I see with even the "horse-safe/pasture-safe" herbicides is NOT with the products themselves, but with the pastures. Many pastures contain weeds that are toxic to horses at some level - not necessarily in the amounts that a horse might ingest during the course of a day's grazing, but in larger quantities and higher concentrations.

Much depends on what sort of weeds you have, what sort of pastures you have, and what your horses like to eat. Horses grazing good-quality pastures will usually ignore weeds; horses grazing mediocre pastures may eat some weeds to supplement the grass; horses grazing poor-quality pastures may have access to so little grass that they are forced to graze weeds if they're going to get anything at all to eat. Even if you take great care of your pastures, you're going to have some weeds here and there - yes, even in well-maintained pastures that are regularly mowed and reseeded when necessary.

We use herbicides to get rid of unwanted, toxic weeds - that's good - but once we've killed the weeds, it's a good idea to remove them from the fields before allowing the horses to go back into those fields and graze. This is because horses often become very interested in dead, wilted weeds that would not have been at ALL interesting when they were still green and growing. Wilting can make some weeds sweeter and more palatable; herbicides cause wilting. If there are weeds in your pasture and you absolutely don't want your horses to eat them, it's safest to take the horses off the pasture, use the herbicide to kill the weeds, and then go in and remove the dying weeds before the horses are given the opportunity to graze them. If you have just a few acres in pasture, this won't be a big job. If you have many acres in pasture - hundreds, say - it will be just about impossible; in that case, your best bet will be to use a safe herbicide and then wait for a week or ten days before you put the horses back out. The wait will ensure that the weeds will be dead and decaying (or dried up, depending on your climate) and not merely wilted; after a week or ten days, they should be MUCH less palatable to your horses.

Weed control can be tricky. Sometimes you do have to use herbicides to achieve good weed control. Goats can also be very effective "weed controllers" - the problem then becomes finding a way to build a fence that keeps your goats IN the pasture. Goat-proof fences are hard to find; someone once said that if a fence will hold water, it will hold a goat, and I tend to agree.

You might ask your county extension agent for some information on the use of vinegar (not the kind we use in the kitchen - a much higher concentration) as a natural herbicide. It can also be useful to grow a variety of pasture grasses in your fields, perhaps also adding some safe pasture herbs, so that your horses can benefit from a varied diet without becoming tempted to break the monotony with a few bites of not-so-healthy weeds. Promoting the plants you want in the pasture is just as important as discouraging the ones you don't want. At the end of the day, your best pasture management strategy is probably just to keep mowing your pastures regularly, so that you can allow the grass to grow and prevent the weeds from crowding out the grass and taking over.

Jessica  http://www.horse-sense.org

Category: Farm/Ranch Keeping

Opinions expressed herein are those of the experts consulted and do not necessarily represent the opinions of the editors and publishers. The information in this publication is for educational purposes only. It is not intended to medically prescribe or diagnose in any way. ~ Holistic Horse Inc.