Roundup herbicide treats some weeds and grasses after they have emerged. The main ingredient in Roundup is glyphosate in isopropylamine salt form. Certain substances effectively neutralize Roundup in the sprayer or in the soil.

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Treat post-emergent weeds like the thistle with Roundup herbicide.

Water

If you use Roundup to treat an area that will later be used for planting, you must neutralize the Roundup with water beforehand. The Roundup label indicates that half an inch of water, through natural or man-made means, will effectively neutralize the product.

Dirt

Do not apply Roundup to the wet dirt area around the weeds and grasses you want to treat, because it will not absorb through the dirt to the root system. Additionally, microbes in the dirt will eventually break down the product. Furthermore, if dirt gets into the sprayer, the dirt will begin to neutralize the product before you even spray it.

Bleach or Ammonia

Use diluted bleach or ammonia to clean sprayers that were used to spray Roundup. Do not use the two products together as they will form chlorine gas, which is toxic.