Spatial and temporal stability of weed populations over five years

The size, location, and variation in time of weed patches within an arable field were analyzed with the ultimate goal of simplifying weed mapping. Ann ual and perennial weeds were sampled yearly from 1993 to 1997 at 410 perman ent grid points in a 1.3-ha no-till field sown to row crops each year. Geos tatistical techniques were used to examine the data as follows: (1) spatial structure within years; (2) relationships of spatial structure to literatu re-derived population parameters, such as seed production and seed longevit y; and (3) stability of weed patches across years. Within years, densities were more variable across crop rows and patches were elongated along rows. Aggregation of seedlings into patches was strongest for annuals and, more g enerally, for species whose seeds were dispersed by combine harvesting. Pat ches were most persistent for perennials and, more generally, for species w hose seeds dispersed prior to expected dates of combine harvesting. For the most abundant weed in the field, the annual, Setaria viridis, locations of patches in the current year could be used to predict patch locations in th e following year, bur not thereafter.