How long is roundup effective?


I have lots of weeds in my garden, but I do not want to use chemicals. If I use roundup in the early spring when the weeds have just started, how long before this chemical is inert?

Posted by: Charlie (1 point) Charlie
Posted: August 3, 2013


When scientists discuss how long a chemical persists they measure it's half-life. How long before half of it is degraded.

This from Monsanto http://www.monsanto.com/products/Docu...
"For example, a Monsanto study conducted at eight sites across
the U.S. in 1992-1993 produced a range of half lives, some short (1.7, 7.3, 8.3 days) and some
longer, up to 141.9 days at one site in Iowa (Oppenhuizen 1993). Anti-pesticide activist groups
often cite the latter result. . The average half-life of glyphosate at the eight study sites was about
40 days, a moderately rapid rate compared with degradation of other compounds. The variability
in rates of glyphosate degradation is believed to be due to the varying microbial activity and extent
of soil-binding at the different study sites."
(note that the Oppenhuizen 1993 is an internal Monsanto document and unpublished but mentioned in another publication).

There are lots of factors affecting how long it persist such as the amount of microbes in the soil and rain. Note that this stuff is very toxic for aquatic organisms so it should not be used near water.

A colleague of mine at Penn State (Dr Chris Mullin, who is an expert on pesticides) said that there have not been a sufficient number of studies by independent research groups to conclude how active a pesticide is and for how long.

Here is an article on the varying opinions of different societies and crop/garden experts on roundup. And what alternatives there are http://www.sustainable-gardening.com/...

Roundup is a chemical that has gylphosate which kills the plant. It is mixed with 59% polyethoxethyleneamine (POEA). This is also toxic and of concern is if that lasts the same of less time as gylphosate. So, in addition to asking how long the active ingredient remains one also has to think about the other ingredients, which also affect human health.

I would say a definitive answer on how long Roundup remains active in the soil is not known. Days to weeks and possibly months. So, the question is whether you are happy with using the product. The choice comes down to whether you are planting food crops on the land. Much of the corn and soy we eat has been grown in fields treated with Roundup.

Here is a side by side comparison of Roundup and Vinegar which I throw in as I like the photos

Posted by: David Hughes (63 points) David Hughes
Posted: August 4, 2013

Most of your spring weeds will germinate around the same time as your first crops, Charlie. Roundup isn't selective, so it'll kill your food plants, too. And because this herbicide works on growing plant tissue, it won't affect weed seeds in the soil waiting to emerge when environmental conditions are right for them.

An alternative to herbicides if you can wait out the rest of this season would be to spread soil amendments and/or fertilizers over the ground--get the soil tested to see what you'll need--then lay down a heavy, weed-suppressing mulch--layers of newspaper or cardboard covered with straw, hay or leaves; black agricultural plastic (sometimes available recycled from farmers who've used it to cover silage mounds, they discard it as waste), or landscape fabric--for the rest of this season. Cover every bit of bare soil that isn't growing crops right now.

The vegetation will die back under the mulch cover, leaving the soil ready for planting next spring. I've opened up lots of new garden spaces this way over the years, even in heavy pasture sod.

You can just open holes in the mulch cover and plant/transplant directly into the sol below in spring, or remove all the mulch, till the soil, and arrange your new beds and rows.

Posted by: Peg Boyles (5 points) Peg Boyles
Posted: August 4, 2013

Tanya in the Garden commented,
Another vote for sheet mulching! The advantage of using cardboard or newspaper, rather than plastic or fabric, is that you will never have to dig it up again. You can leave it in place and it will feed the worms.

Some weeds will die back when they are smothered, but perennial weeds with strong roots may persist. For those weeds (bermuda grass and bindweed in my area), I try to remove as much as I can before sheet mulching or starting a garden, and then I make sure to pull the ones that appear as soon as I see them.

In Sacramento, another option right now is solarization, assuming you're not gardening there now. For details, see http://www.ipm.ucdavis.edu/PMG/PESTNO...

over 9 years ago.

While I don't have a scientifically researched answer for you, I do know that the chemicals used in most herbicides marketed in mass for the last 15-or-so years are extremely toxic even if used in low levels. RoundUp would probably kill weeds for a season in recommended doses at first. But the weeds in your garden will develop an immunity to the ingredients in the product over time and you'll have to use more and more to get the desired results.

If Glyphosate RoundUp is used in a garden space that you ever plan to use for real organic gardening, the resulting produce will not be "organic" by any stretch of the word.
These products leave chemicals and compounds in the soil that cannot be removed. Yes, many of the ingredients will "flush" out, but trace residues- including bio-available toxins (meaning plants will absorb them and then you will when those are eaten).can be found for many, many, many years after.
I would steer clear of any of these products. If you need to kill weeds- pull them. If that doesn't work get your kids to do it or lay fabric under a raised bed to prevent them from coming up en masse next time.

And for the love of God, someone correct me if I'm wrong. These statements come from first-hand knowledge as well as many months of self-study.
Good luck.

Posted by: Tom (2 points) Tom
Posted: August 3, 2013

David Hughes commented,
It is true that 'immunity' can occur. We speak of that as a plant evolving resistance to Roundup. This has happened multiple times and is increasing at a very fast rate (see figure 2 in this extension document https://www.extension.purdue.edu/extm...)
But this happens on farms where very high levels of pesticide are applied so the pressure-what we call the selective pressure- is high. You would expect such a high pressure in a garden (under usual practices).

over 9 years ago.

Roundup is not the gentle killer that its manufacturer describes.

Cardboard and mulch are what I use. Mow as close as practical for grass and such, dig/chop/remove for the larger stuff. Lay down your cardboard so it overlaps by at least 6" or so, and plug any cracks with torn off flaps of cardboard, and lay your mulch on top. If you have the option, wet it all down. Cardboard won't stay in place in wind unless you cover it with hay or piled weeds, etc, and getting it wet helps keep it down, too. If you live in a really windy place, you might need to hold it down with rocks.

You can often get cardboard from furniture stores or manufacturing places. Many places have bins and stacks for the cardboard recyclers; go in and ask if you you take some of their larger pieces. Promise (and keep that promise) that you will leave the area neat and tidy.

The first time I did this, I was shocked at how good the soil looked when I raked the decomposing cardboard and mulch aside.

Posted by: FussyOldHen (16 points) FussyOldHen
Posted: August 8, 2013

I would suggest you not use synthetic chemicals. I find that weeding is minimal with mulching. A quick raking before you plant will loosen the weeds that have sprouted. I find that if I think of gardening as a stretching exercise, and a way to destress, then I am more motivated to use my fingers and enjoy the "feel-good chemicals" our body will release. A word of caution: like any thing good, gardening may become habit-forming. So, expect to make more and more gardens. To keep your gardening habit in check, be sure to cultivate several healthy hobbies.

Posted by: Joan Ribbons (4 points) Joan Ribbons
Posted: August 19, 2013

Never use Monsanto chemicals. Round up kills the soil for 50+ years and also does the Monsanto GE seeds, that live on those chemicals and that is what you eat when you eat GE crops. Poisons !
simple dish soap (reg like Dawn) and water bath is all most plants need to stay free of problems.

Posted by: Little Bright Feather (1 point) Little Bright Feather
Posted: August 31, 2013

Round up is very dangerous to you and the soil and the toxins will be around for years.

I suggest you cut all the weeds close to the ground with a mower or whatever you have and leave them where they drop. Cover them with 6 to eight layers of newspaper, then put a few inches of mulch on top.

The newspapers will block the light and kill the weeds which will then rot down and feed the soil. Easy draining mulch on top will keep the soil moist and cool when the sun is hot and will eventually rot down to feed the soil more. While the mulch is still light and not rotted very few weeds seeds will grow because they cannot reach the soil and will be cooked in the sun.

This is a very cheap and easy solution that also makes your soil more fertile. If you have chicken manure add that before you put the newspaper down. I live in the tropics so I use a 3 inch layer of rice hulls and coconut coir for mulch. When you plant seedlings just move the mulch aside and poke a hole in the newspaper. Don't leave mulch touching the plant. I have had as many as three successive crops before I needed much weeding.

Posted by: Frank Woolf (1 point) Frank Woolf
Posted: September 1, 2013

You need to log in if you'd like to add an answer or comment.
Heart Heart icon