CROP-WEED COMPETITION AND HERBICIDE PERFORMANCE IN CEREAL SPECIES AND VARIETIES

In dose-response experiments with the herbicide combinations MCPA+dichlorprop and ioxynil+mecoprop in barley, winter wheat, and winter rye varieties, oilseed rape (Brassica napus L.) was used as a substitute for weeds. The results showed a significant interaction between the competitive ability of varieties and herbicide performance. A negative exponential model with variety as categorical variable was used to analyse the data and to assess the competitive effect of the varieties on herbicide efficacy. A target level of 5 g weed dry matter m(-2) in all varieties at the end of flowering was used to derive a varietal calibration factor of the herbicide dose. The results showed significant differences in calibration factors between species of winter wheat, barley, and rye, and between varieties of spring barley and winter wheat. In the winter wheat variety Sleipner it was necessary to use a 154% higher herbicide dose than in the winter barley variety Trixi, whereas in the winter rye variety Petkus II, herbicide dose could be reduced by 31% compared with Trixi. The differences between spring barley varieties were smaller but significant.