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This year I would like to get rid of weed around wire fence and I'm considering using herbicide.

As much as I can see all non-selective (glyphosate) herbicides available at local stores have no information about withholding period (after what period it would be safe to plant or consume fruit/vegetables).

Is it safe to use such herbicides and how long should I wait before planting?

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This Monsanto page says that it depends on the strength of the product used. For the product used on perennial weeds, wait 72 hours. Glyphosate is a contact killer that is taken up by the leaves, and then taken down into the roots. It's supposed to be safe anyway in that there are no mammalian metabolic pathways that can be affected by this chemical.

However, the WHO claims that glyphosate may be carcinogenic linking it to Non-Hodgkins lymphoma.

There are lots of non-chemical ways of dealing with weeds that you might want to also consider.

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  • Is this withholding period of min. 72 hours same for all glyphosate based herbicides regardless of manufacturer/brand? Does herbicide concentration or way of application make difference (spraying or applying directly)?
    – False Identity
    Commented Jan 16, 2018 at 20:58
  • They use the strongest concentration for perennial weeds. For annual weeds you can use a shorter period before planting - 24 hours
    – Graham Chiu
    Commented Jan 16, 2018 at 21:28
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    Note that they put other ingredients in glyphosate fertilizers besides glyphosate. Graham, do you know if those ingredients differ in more than concentration from product to product? If they do, Monsanto's official answer could be pretty variable. (I say 'Monsanto's', because of course, not everyone agrees about what is safe with glyphosate, and how long to do what).
    – Brōtsyorfuzthrāx
    Commented Jan 16, 2018 at 23:51
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    @Shule I was under the impression that the main thing else they added were surfactants to allow it to stick to leaves. And these have their own toxicities. But each manufacturer has its own surfactant that they add to glyphosate so one should look at the documentation if available for the product being used.
    – Graham Chiu
    Commented Jan 17, 2018 at 0:41
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When I was in pesticide...school, grins, there was an instructor who laughingly said you could drink this stuff. ha ha.

The chemistry of glyphosate changes the second it is sprayed on another surface. It does not leach. It is systemic, not contact. It is transported through the phloem from the leaves to the roots. This is where the damage is done, glyphosate ruins the roots. It takes 3 weeks for complete kill. It takes 3 weeks to be able to plant seeds in that soil.

When used correctly, glyphosate worked well. Too bad now we have to EAT this glyphosate in our food. Corn and other plants have been genetically programmed to be part glyphosate. They can spray glyphosate on crops without hurting the crops. Just the weeds. Now in my opinion that is like going after a couple of bad guys running around in New York City...with a nuclear bomb. Killing everything including the two dumb criminals. Guess it makes more money for the agricultural company.

But using roundup or glyphosate properly once every 5 years? Can be labor saving and judicious. But not be part of our food...

The MSDS sheets, that I had to read every single time I used glyphosate said 3 weeks for planting new plants or seed. If you buy gmo corn, you get to EAT it. A bit different, huh?

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  • If you drink the stuff, you tend to die
    – Graham Chiu
    Commented Jan 17, 2018 at 3:37
  • Not a fact, Graham. I would want to die because I was stupid enough to drink that crap! But we drink and eat fluoride every day which is far far worse than glyphosate. Go figure.
    – stormy
    Commented Jan 17, 2018 at 3:39
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    I had to post this youtu.be/ovKw6YjqSfM regarding drinking this stuff.
    – False Identity
    Commented Jan 17, 2018 at 8:17
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    @stormy 3 weeks seems more reasonable period than 72 hours Graham mentioned in his answer. Just would like to know if it is 3 weeks after application or 3 weeks after weed is officially 'dead'?
    – False Identity
    Commented Jan 17, 2018 at 8:20
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    Stormy - Glyphosate is a contact herbicide in that it only affects plants that it touches, which is why drift is an issue with it. Once it touches and enters a plant, it inhibits the EPSP synthase enzyme, which plants require. This is what kills the plant.
    – Jurp
    Commented Jan 18, 2018 at 0:58
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Depends on what concentration you used? I often buy premade products that are used straight from purchase- in theory one shouldn't have to touch or make a batch without touching the chemicals used. However I find many containers or sprayers used in the their design leak everywhere or seep out on hot days! This is what it says on my stuff I buy: safe to replant or cultivate within 7 to 10 days after use anytime between May and September. However! if one reads more, it then says the effectiveness of the product can take from 1 to 4 weeks for the stuff to do its job? so your guess is as good as mine? No conclusion is offered because industry doesn't like to rubber stamp themselves into an impossible legal situation- is it safe or not, one minute it is and then the next like stormy hints there are health issues- I should say no one I've come across in the industry has a definitive answer too, and I was quoting a direct piece of literature from the actual bottle of weedkiller I use at work. needless I was surprised by the bottle offered as advice? no wonder everyone is confused...

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  • I don't see why is this posted as an answer. No conclusion is offered. The original question (that is about herbicides without witholding data) is not addressed at all. This should be a comment, IMHO.
    – VividD
    Commented Jan 27, 2018 at 16:05
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    I have upvoted a lot of your answers, but not this time. This doesn't provide an answer as to how many days should pass before planting again after applying glyphosate. Please, at least provide the name and the concentration of "your stuff" that requieres 7-10 days. Currently your answer is in the low quality review queue and I admit I was tempted to press "recommend deletion", but I guess you could use a chance to add those details before me or somebody else votes to delete. It's nothing personal, it happened to all of us at some point.
    – Alina
    Commented Jan 28, 2018 at 13:09

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