The effects of weed residue management on pests, pest damage, predators and crop yield in upland rice in Cote d'Ivoire

The effects of weed residues on the abundance and activity of generalist ar thropod predators and insect pests and on rice yields in upland rice were s tudied. Weed residues were placed in the experimental plots in three ways: (1)residues left in situ where weeds are uprooted; or (2) placed in small p iles throughout the field; or (3) removed from the field but heaped at the edges to be burnt when dry. The study investigated the effects of residue d isposal in upland rice under research station conditions designed to simula te conditions in farmers' fields. Spider activity was significantly greater in plots with scattered residues and strips of residue and least in plots from which residues had been remov ed. Staphylinid beetle activity was significantly greater in plots with a s upplementary weed mulch than in other treatments. By contrast, spider densi ty was greater when residue was piled or used as mulch rather than when sca ttered but the smallest populations occurred in the no-residue plots. Carab id beetles were significantly more abundant in plots with strips or piles o f weeds and staphylinid beetles were most abundant in the mulched plots. An ts were not affected by weed residue placement. Among the ten pest groups studied, the abundance of only Chaetocnema sp., w as significantly greater in plots with strips and piles than in other treat ments, populations of other pests being unaffected by weed residue placemen t. In 1994, mean percentage of deadhearts (stem-borer damage) was significa ntly greater in the residue-free plots than in other treatments but in 1995 the differences between treatments were not significant. In both years, gr ain yield was not affected significantly by weed residue placement but was lowest in the residue-free plots.