Use of herbicide mixtures for pre and post-emergence weed control in sunflower (Helianthus annuus)

Three field experiments were carried out on sunflower (Helianthus annuus L.) from 2002 to 2004 in central Italy, to assess weed control efficacy and selectivity to the crop for some herbicides. These were used in pre or post-emergence applications at different doses and in different mixtures. All herbicides showed a good selectivity to the crop; however, oxyfluorfen in pre-emergence and aclonifen in post-emergence showed some transitory phytotoxicity effects, with no damage to crop yield. Considering pre-emergence applications, mixtures with s-metolachlor gave best control of grasses, followed by mixtures with flufenacet. All herbicides gave a very good efficacy against broadleaves, except linuron in the case of Polygonum lapathifolium L. In presence of mixed infestations (grasses+broadleaves), s-metolachlor+aclonifen and s-metolachlor+oxyfluorfen seemed to be the best options for pre-emergence weed control. Considering post-emergence applications, aclonifen showed a satisfactory efficacy against broadleaves and its weed control spectrum could be completed by mixtures with quizalofop-ethyl. However, this option seemed to be advisable only with high grasses infestation levels. Differences in crop yield were on average small with yield levels of pre-emergence treatments higher than those of post-emergence treatments. Otherwise, high infestation levels during the early crop stages caused severe damage to crop yield, in the cases of insufficient weed control.