Growth, competitiveness, and seed germination of triallate/difenzoquat-susceptible and -resistant wild oat populations

Understanding the relative competitiveness and seed germination patterns of herbicide-resistant weeds has implications for integrated weed management. Replacement series experiments were conducted in the greenhouse to compare interspecific competition among two triallate/difenzoquat susceptible (S) and 10 resistant (R) wild oat (Avena fatua L.) populations. Each series included monocultures of each of the populations and three mixtures at relative S:R proportions of 3:1, 1:1 and 1:3. Shoot dry weight tended to be greater in the R than S populations, but results were not always statistically significant at the 5% level. Leaf area was more variable, but in most cases did not differ between R and S populations. With a few exceptions, relative crowding coefficients for shoot dry weight and leaf area were similar for S and R populations indicating little or no differences in competitiveness. In field experiments where two S and five R populations were grown in competition with wheat (Triticum aestivum L.), two of the R populations produced significantly (P < 0.05) greater shoot dry weight and seed yield than the S populations. Otherwise populations did not differ significantly. In seed germination studies, the S populations consistently displayed lower cumulative germination than the R populations. The higher seed germination associated with the R populations suggests that producers should be able to manage these populations effectively with a combination of alternative herbicides and cultural practices.