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Does Glyphosate (Roundup) Lose Potency Over Time?

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It’s not uncommon for lawn maintenance chemicals to sit around in the garage for several months or even years. Knowing which ones are fine to use and which should be disposed of due to lost effectiveness is a common question.

Glyphosate (Roundup) can lose potency over time but generally has a long shelf life if kept tightly sealed in its original container and stored in a dry, cool, and frost-free environment. Once mixed with water, glyphosate begins to degrade after about three days and remains viable for about a week. 

In this article, I will explain how glyphosate (Roundup) breaks down when mixed with water and after it is applied to the soil so that you know how to use it safely and in the appropriate amount. I will also describe how you should store leftover Roundup and dispose of it safely. 

How Long Does Glyphosate Stay Active For?

Glyphosate may stay active for up to a year in the soil following treatment. However, it takes only a few days to a week for 50% of the Roundup to completely disappear from the environment. After a year, residual glyphosate in soil and sediments is not considered toxic.  

Glyphosate binds tightly to soil particles. So, although it may stay active in the soil for several months, it does not usually leach into water bodies. These low-level residues are also not taken up by plants. 

Glyphosate is broken down by soil and water microbes like bacteria and fungi. It is also readily dispersed by plants. However, the rate of degradation depends on the level of microbial activity that, in turn, depends on environmental conditions like rainfall and heat. 

For instance, glyphosate degrades quickly in warm and moist soils rich in organic matter because microbial populations and activity are higher in such soils. 

According to a study, about half the glyphosate in a litter of dead leaves degraded in 8-9 days. Soil microbes feed on fallen leaves, so leaf litter houses a sizable microbial population.

Ground Level View of a Lawn

How Long Is Glyphosate Active Once Mixed?

It is good to mix only the amount of glyphosate (Roundup) you need to treat your lawn. However, you may sometimes end up mixing more than you need. 

Glyphosate is active for about a week once mixed with water which starts the degradation process. Half of the glyphosate can completely degrade between 3 days and 19 weeks, depending on water conditions like temperature and pH levels.

Because glyphosate is salt-based, you might find Roundup settling down at the bottom of the container some days after mixing. Do not worry; it is still viable. After shaking the container, you can use it to remix the Roundup with water.

Why Roundup Won’t Go Bad?

Roundup doesn’t go bad for a long time because its primary active ingredient, glyphosate, is non-volatile. It doesn’t degrade in the presence of light and is also stable in the air. Most herbicides are designed to have a long shelf life of at least five years if stored correctly. 

Both the concentrate and the ready-to-use formulations of Roundup can last almost indefinitely if they are stored in their original containers with the lid tightly shut and kept away from heat. 

How To Store Glyphosate Correctly?

A Roundup Container Sitting in Grass

Although it is always a good practice to buy only as much glyphosate (Roundup) as you need for the current growing season, most of us have at times erred with our estimates and ended up buying more than we needed. 

Because glyphosate does not go bad for a long time, you must ensure that you store it correctly and safely. 

Here’s how to store glyphosate correctly:

  • Store it in its original container with the label intact.
  • Seal the container securely.
  • Keep the container in a dry, frost-free, airy, and relatively cool place. 
  • Keep it out of reach of children and pets, preferably in a locked storage cupboard.

As per the Environmental Protection Agency (EPA), all herbicides must carry storage instructions on the container or the label. So, make sure that you also check for these.

You should NEVER:

  • Keep glyphosate in drinking water bottles. 
  • Store it near food items, seeds, fertilizer, or other pesticides. 
  • Store it in an area where food and beverages are prepared or consumed.
  • Place the container of glyphosate on an unstable base from where it can fall off and leak.
  • Place the container within 200 feet (60.96 m) of a water body. 

How To Safely Dispose of Leftover Roundup?

To safely dispose of leftover Roundup, you should follow the guidelines set for disposing of hazardous household waste. You should contact organizations like the state environmental agency and the local waste management authority, who will instruct you on how to dispose of leftover Roundup. 

The glyphosate in Roundup is a cancer-causing agent. If disposed of improperly, it can contaminate drinking water supplies, leach into water bodies, and pollute the environment. Exposure to Roundup can harm aquatic life, plants, animals, and humans.

Here’s what you should do to dispose of unused Roundup properly:

  • Check the product packaging for any specific disposal instructions. 
  • Get in touch with your local waste management authority, state environmental agency, or health department to find out how you can dispose of hazardous waste.
  • You can also call 1-800-CLEANUP or visit the Earth911 website to find out how you can dispose of leftover Roundup.
  • You can get in touch with local nurseries, garden centers, landscapers, or farms to find out how they dispose of unused Roundup.

If you have unused Roundup at home, NEVER:

  • Throw it in the trash.
  • Flush it down the toilet.
  • Dump it in the drain.
  • Pour it down the street drain.

Also, when handling Roundup, ensure that you take the following safety precautions:

  • Wear disposable gloves. 
  • Wear protective eye coverings.
  • Thoroughly clean the container where you had stored Roundup. Then recycle the container. Never use it to store anything that humans or animals will likely consume. Leftover glyphosate can leach into anything you keep in the container.
  • Dispose of the gloves and eyewear.

Conclusion

Glyphosate is a powerful weed killer but a hazardous substance as well. Using it responsibly means:

  • Buying only the amount that you intend to use during a growing season
  • Applying only as much as needed
  • Storing it according to recommended storage instructions
  • Disposing of it safely following guidelines

For more, check out How Long Does Roundup Weed Killer Last In The Soil?

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