How Can I Control Common Knotweed?

Do you want to try controlling common knotweed with cultural control methods?

Do you want to control common knotweed with aeration?

Do you want to control common knotweed with mulches?

Do you want to try controlling common knotweed with chemical control methods?

Do you want to prevent common knotweed from emerging?

Loosening the soil in lawns to provide better drainage and a better environment for more desirable species can be beneficial. If areas are compacted, loosen the soil and overseed with a locally adapted grass seed.

A variety of mulches can be applied to planting beds and other landscaped areas to prevent the establishment of common knotweed. Mulching with landscape fabrics can be effective if the fabric is overlapped and no light is allowed to penetrate the soil. Use polypropylene or polyester fabric or black polyethylene (plastic tarp) to block all plant growth. Rock or organic mulches such as bark or compost can be used over the top of synthetic fabrics. If used alone, organic mulches should be 3 to 4 inches thick. Finer mulch material is not desirable since weeds seeds may easily grow in it.

Common knotweed is easy to remove with common weeding tools, such as a swivel hoe. For the home gardener, frequent manual removal along with mulching should be sufficient to manage this weed in most situations.

Preemergent herbicides must be applied before the knotweed seed germinates. Examples of preemergent herbicides available for home use include products containing benefin, dithiopyr, oryzalin, pendimethalin, prodiamine, and trifluralin. The following additional preemergent herbicides are only available to licensed pest control operators: atrazine, hexazinone, napropamide, oxadiazon, pronamide, and simazine.

Postemergent herbicides like those containing dicamba (for use in turfgrass only), glyphosate, and pelargonic acid will control emerged common knotweed. For best results, these herbicides must be used while the weed is young, preferably in the early seedling stage, before it becomes more established and hardened off. When knotweed is young, it can be controlled with 2,4-D, and there are several products available for home use that contain this chemical. Some post-emergent herbicides kill the top growth of a plant, but it may regrow from buds on the crown of the plant.

One of the most important management methods is to prevent soil compaction, which provides the conditions under which this weed grows best. Arrange landscapes so that soil is less likely to become compacted. Spread out foot and vehicle traffic over a broader area. Use fences or hedges to reduce traffic and install rock or pavement pathways where traffic cannot be avoided. Do not trample areas soon after irrigation or rainfall. Arrange soccer fields and athletic areas so that heavily used areas such as goals, midfields, and sidelines can be rotated.