Commonly called dog grass or couch grass, quackgrass (Agropyron repens) is a noxious perennial weed that spreads by rhizomes---horizontal stems that grow 2 to 3 inches below the surface of the soil. Native to parts of Europe, Africa and Asia, quackgrass is difficult to remove because of its intricate roots and requires thorough digging to prevent re-growth from traces of roots left behind. Several plants naturally compete with this weed and inhibit it from spreading across the area.
Vine Legumes and Corn
A few vegetables successfully compete with quackgrass, even though their growth is sometimes stunted. Vine legumes such as green beans survive areas with quackgrass infestations, although their yield is likely to decrease.
Quackgrass releases negative alleopaths in the soil that retard and stunt nearby plant growth. Corn and other tall plants survive this biological phenomenon, although the height of cornstalks is sometimes stunted.
Cucurbitaceae or cucurbits is the creeping plant family that includes gourds, cucumbers, melons, watermelons and squashes. Smother the competing quackgrass by spreading a weed barrier over it and drill holes through it into which you will plant cucurbit seedlings. Make sure the seedling roots touch the soil so the tops spread over the weed barrier. The quackgrass underneath the barrier suffocates eventually due to lack of contact with sunlight, air and water, and becomes weak enough to be pulled out along with the roots by the end of the growing season, which is usually six to seven months after planting seedlings.
The strong rhizomes quackgrass produces can cut through underground or root vegetables such as carrots. Potatoes survive competition with quackgrass, provided the seeds are planted deep in the soil to escape spreading rhizomes that could choke it out. Applications of pesticide on the grass above will help the seeds germinate and develop into healthy vegetables. Also, constant tillage required by growing potato plants is detrimental to quackgrass.
Some winter grains such as buckwheat and winter rye develop in fall and early spring when temperatures are cool, just like quackgrass, hence competing with each other directly. For maximum benefit from this competition, sow high densities of winter grain (200 kg/ha). Buckwheat germinates quickly to block sunlight penetration to the plants around, including quackgrass. However, this competition is short lived because light filters through once flowers develop. Buckwheat should not be harvested but used to form a green manure crop along with other crops that nurture the soil and eliminates the invasive weed. Sorghum is another strong grain that withstands competition and grows high enough to overshadow quackgrass.