Weeds with deep roots can infiltrate and damage the leach field.
The leach field of your septic system is the final step in filtering wastewater from your home. Normally only grass is allowed to grow over the field, but if weeds have taken over, you can kill them without digging into the soil. A glyphosate product such as Roundup kills the weeds, and everything else, down to the roots. While ready-to-use products are available, applying a Roundup concentrate is an economical solution to the weed problem.
Stop mowing two weeks before applying the Roundup, so the weeds are growing vigorously.
Wait until a clear, windless day when the temperatures are above 60 degrees Fahrenheit.
Put on safety gear, including long sleeves, long pants, chemical-resistant gloves, safety goggles and a breathing mask.
Pour the Roundup concentrate in a hose-end sprayer, setting the dial at 6 ounces per gallon. One quart of concentrate makes up to 10 gallons of solution, which treats an area up to 3,000 square feet.
Spray the Roundup onto the weeds over the leach field, wetting the leaves' top and bottom with the solution. Avoid spraying any desirable plants as Roundup kills all vegetation.
Wait up to two weeks to ensure that all the weeds are dead. Roundup is absorbed by the leaves of actively growing plants, killing them down to the roots. However, some plants are so vigorous that they require more than one application of glyphosate, the active ingredient in Roundup.
You can scatter grass seeds or flower seeds three days after applying Roundup; no residual will be left in the soil.
Avoid disturbing the soil over the leach field; you risk exposure to harmful bacteria and damaging the leach lines.
Only plant shallow-rooted grasses and flowers over a leach field. The roots of shrubs, trees and deep-rooted flowers may damage the septic system.
United States Environmental Protection Agency: The Basics -- What Is a Septic System?
de, Ruth. "How to Use Roundup on Leach Fields." Home Guides | SF Gate, http://homeguides.sfgate.com/use-roundup-leach-fields-86391.html. Accessed 22 April 2019.
How Much Water Do You Use With 48 Ounces of Roundup?