Investigations for using weed thresholds in transgenic rape

Since the vegetation period 1998/99 in Germany 8-10 field trials were carri ed out for the examination of weed thresholds in systems with herbicide tol erant winter oilseed rape against non selective herbicides. The field trial s will be conducted over a three year period. Contents of the examination a re the practicability of the weed threshold model, the advantages or disadv antages of the system "herbicide tolerant winter oilseed variety - non sele ctive herbicide" and an economical evaluation of these systems in compariso n to systems with conventional herbicide application. The application of th e non selective herbicides is carried out post emergence in autumn regardin g weed thresholds and will be compared with an prophylactic application of non selective herbicides, an usual application of conventional herbicides a nd an early post emergence application of conventional herbicides in winter oilseed rape regarding weed thresholds. The first one year results show th e effectiveness of the existing weed threshold model in systems with herbic ide tolerant winter oilseed rape varieties and non selective herbicides. Th e results indicate advantages of these new systems because of a higher temp oral flexibility for the application using non selective herbicides. An eco nomical evaluation yet was not carried out.