Johnsongrass is an aggressive perennial plant that can invade primarily row crops, CRP, roadsides and non-cropland areas.  It is rarely found in pastures as cattle will readily find it desirable as forage.  However, it can become toxic if more mature plants are found by cattle in drought conditions or during early frost.  Johnsongrass spreads by seeds and rhizomes.  A mature plant may grow over 8 feet tall and produce thousands of seeds and many feet of rhizomes.  Seeds may remain viable for up to 25 years.