Spatial stability of Avena sterilis ssp ludoviciana populations under annual applications of low rates of imazamethabenz

Long-term experiments were conducted in two winter barley fields in central Spain to determine the spatial stability of Avena sterilis ssp. ludoviciana populations under annual applications of low rates of imazamethabenz herbicide. Weed density was sampled every year (over 5 years in the first field and over 3 years in the second) on the same grid locations prior to herbicide application. Although weed patches were stable in their location, weed density decreased in most of the years. In the first field, the populations decreased exponentially over the 5-year period. The rates of population decline were dependent on the initial density of the population, being higher for the central core of the patches and lower for the low-density areas. Under the conditions present in this experiment, it was possible to reduce heavy weed patches (up to 1200 seedlings m(-2)) down to relatively safe levels (18 seedlings m(-2)) in a period of 3 years using a density-specific control programme, applying low rates of herbicides when weed densities were below a given level (1000 seedlings m(-2)). However, under adverse environmental conditions, half rates of the herbicide failed to control the weed populations adequately. The stability of the location of patches of A. sterilis ssp. ludoviciana suggest that weed seedling distributions mapped in one year are good predictors of future seedling distributions. However, the actual densities established each year will depend on the control level achieved the previous year and the climatic conditions present during the establishment period.