The size, location, and variation in time of weed patches within an arable field were analyzed with the ultimate goal of simplifying weed mapping. Annual and perennial weeds were sampled yearly from 1993 to 1997 at 410 permanent grid points in a 1.3-ha no-till field sown to row crops each year. Geostatistical techniques were used to examine the data as follows: (1) spatial structure within years; (2) relationships of spatial structure to literature-derived population parameters, such as seed production and seed longevity; 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 generally, for species whose seeds were dispersed by combine harvesting. Patches were most persistent for perennials and, more generally, for species whose 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 the following year, but not thereafter.

Nomenclature: Amaranthus retroflexus L. AMARE, redroot pigweed; Asclepias syriaca L. ASCSY, common milkweed; Brassica kaber (DC.) L.C. Wheeler SINAR, wild mustard; Chenopodium album L. CHEAL, common lambsquarters; Cirsium arvense (L.) Scop CIRAR, Canada thistle; Elytrigia repens (L.) Nevski AGRRE, quackgrass; Setaria viridis (L.) Beauv. SETVI, green foxtail; Glycine max (L.) Merr., soybean.