EFFET DES APPLICATIONS REPETEES D’HERBICIDES ET DES DATES DE PREPARATION DU SOL SUR LES CHANGEMENTS DE POPULATIONS DES MAUVAISES HERBES

The immediate and residual effect of diclofop methyl (2(4-(2,4-dichlorophenoxy)-phenoxy propionic acid methyl ester)), diclofop methyl plus 2,4-D ((2,4-dichlorophenoxy) acetic acid), and the 2,4-D/mecoprop (2,(4-chloro-1-tolyl oxy) propionic acid)/dicamba (3,6-dichloro-o-anisic acid) mixture applied during 2 consecutive yr and for two dates of soil preparation has been evaluated on plots sown and unsown with oats (Avena sativa L.). The population changes observed during the 2 yr of herbicide applications have been related to the nature of the products and were of short duration. No difference between the herbicide treatments has been observed 1 yr after the treatment. Soil preparation in early June and the presence of oats have reduced considerably the weed populations during the 2 yr of herbicide applications. This effect has been noticeable 1 yr after the treatments. Herbicides are not solely responsible for weed population changes. From this study, it appears that cultural practices play a role as important as herbicides in controlling weed populations at least on a short-term basis.