Management of Sinapis alba subsp. mairei winter cover crop residues for summer weed control in southern Spain

Sinapis alba subsp. mairei (H. Lindb. fil.) Maire, a wild subspecies of S. alba L., which is distributed throughout the Mediterranean basin, has been recently introduced in southern Spain as a winter cover crop in olive groves. The reason behind using this cover crop is for the reduction of Verticillium dahliae inoculum. The effectiveness of this cover crop for weed control has not been assessed to date, despite weed flora in olive groves being highly diverse and competitive, especially in spring and summer, when rainfall is low, temperature is high and crop water needs are at their maximum. The objective of this work is to assess the ability and optimum management of S. alba subsp. mairei cover crop residues for controlling summer weeds. This work offers a more detailed study of the influence of this cover crop on the seedling emergence of Amaranthus blitoides (prostrate pigweed) and Chenopodium album (common lambsquarters) in rainfed field conditions. A factorial design was conducted during the 2002 and 2003 seasons. The studied factors were the following: (1) S. alba subsp. mairei cover crops versus bare soil; (2) two different S. alba residue management techniques after mowing and chopping (incorporation into the soil with shallow tillage versus leaving the residues as a mulch); and (3) the effect on two artificially sown-out summer weeds (prostrate pigweed versus common lambsquarters). The S. alba subsp. mairei cover crop residues reduced the weed infestation by 50 and 60%, and it delayed weed appearance by 3 and 4 weeks the first and second years, respectively, compared with bare soil. The optimum cover crop residue management for weed control was to leave mulch. This management was especially efficient for controlling prostrate pigweed, whether no differences were found for common lambsquarters control when the residues were incorporated into the soil with tillage. These results indicate the great ability of S. alba subsp. mairei cover crop residues to provide summer weed control in rainfed field conditions. Its use, therefore, can contribute to the reduction of the number of herbicide treatments in olive groves.