Da. Derksen et al., IMPACT OF POSTEMERGENCE HERBICIDES ON WEED COMMUNITY DIVERSITY WITHINCONSERVATION-TILLAGE SYSTEMS, Weed Research, 35(4), 1995, pp. 311-320
The influence of herbicides on weed community dynamics is an issue of
agroecological concern. A field study was initiated in 1986 with zero-
, minimum-, and conventional-tillage systems. In 1989 and 1990, the fo
urth and fifth years of study, weed community diversity and relative c
omposition were assessed prior to and following the application of pos
t-emergence non-residual herbicides. Weed communities were assessed at
the level of tillage system to balance the effect of different crop s
equences and crop-herbicide combinations within each comparison. In ge
neral, herbicides did not reduce community diversity when compared by
Shannon's H' and dominance-diversity curves. An increase in species ri
chness and evenness, as assessed by Shannon's E and Margalef's D-MG, o
ccurred in some cases. Differences in relative community composition a
mong tillage systems were apparent before the application of herbicide
s, but disappeared following herbicide application. The use of herbici
des in this study reduced weed densities, maintained weed diversity, a
nd inhibited community changes that were due to changing tillage syste
ms.