Rhizomes (underground stems) are yellow to white, 1/8" in diameter, with distinct joints or nodes every inch or so. Each node is capable of producing fibrous roots, and sending a new blade of grass through the soil. The creeping rhizomes are so tough they can grow through a potato tuber, or push up through asphalt pavement. If left to grow, they will form a dense mat 4" thick in the upper part of the soil. One plant can produce 300 feet of rhizomes each year. Never use a rototiller where quackgrass is growing, because it amounts to propagating thousands of new plants from the chopped up rhizomes.
-----------------------------------------------------------------------------------------------------------Does anyone know of a chemical that will kill quackgrass but not harm iris? I have several iris beds that are heavily overgrown with quackgrass and it's too much work to dig everything up and replant the iris. Done that several times already. Thanks.
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Glyosphate will kill it and here is how it's done in your iris. After the iris begin to go south, mow them off at a high mower setting. When the grass regains some height place a container over the plants and then using a paint roller with a long reach handle apply the glyosphate. By rolling in two or more directions with the paint roller better contact is assured and is far superior to spraying while using less product. Any grass in close proximity to the iris that was covered with the container is to be dealt with after the initial application by directing it away from the iris and applying the glyphosate with a small brush or other suitable applicator.