Knotweed prefers the hard, beaten pathes across lawns, and the compact soil next to driveways. It is an annual that germinates with the first warm temperatures of spring and the first tiny shoots of knotweed are often welcomed as a cover of new grass. It soon branches out and forms a tough, wiry prostrate mat. Knotweed not only prevents the growth of desirable grass, but also produces a great quantity of seed for next year's regrowth. Leaves of knotweed are blue-green, about one inch long and one quarter inch wide. Each leaf is narrow at the base and rounded at the tip. The tiny white flowers are very inconspicuous and are found at the junction of leaf and stem. Knotweed is a particular problem on football fields where compaction and traffic are excessive.