We recently received a call from a customer wondering what to do about knotweed that had appeared on his athletic fields. In an All Natural Organic Turf Care program it is important to grasp the fact that weeds our indicators of underlying soil conditions. Years of chemical usage to control weeds have just served to mask poor underlying soil conditions.
From Weeds of the Northeast (author’s emphasis): “Prostrate knotweed is a summer annual. Is one of the first summer annual weeds to emerge in the spring. In turfgrass, it is most often found on hard compacted soil or areas damaged in spring or summer by traffic or trampling, including paths and walkways and athletic fields. Prostrate knotweed is not particularly competitive; it usually survives in stressed areas where other species do not grow well or are damaged.”
So the good news is that prostrate knotweed grows where nothing else wants to grow. It is also an annual (goes from seed to seed in one year and doesn’t overwinter as a viable plant) and is not particularly competitive; so if you relieve the conditions that favor its growth this year it is less likely to be there next year. So the key is to relieve the areas of compaction and get turfgrass growing in its place. The addition of calcium to the soil in the form of calcitic lime if the pH needs adjustment or as gypsum and the use of humates will help improve the soil conditions. Continued timely aeration of the fields with overseeding this fall is the best way to care of the problem of prostrate knotweed. Traffic (foot and vehicle) should be limited in these areas in the spring especially when soil conditions are wet.