The role of water availability on weedcrop interactions in processing tomato for southern Italy

Anthropogenic climate change is projected to increase the occurrence of drought for the Mediterranean region. The aim of this study was to quantify the role of increasing drought on weed-induced crop losses and cropweed interactions for processing tomato grown in southern Italy. Field experiments were carried out during 2008 and 2009. Two levels of water availability were imposed to compare weed competitive effects under irrigated and rainfed conditions on tomato as a means to quantify weedcrop interactions and associated crop losses when water is limited. In this study, the absolute decline in tomato yields by weed interference was a direct function of water applied (rain + irrigation); however, the relative effect of weed biomass on crop loss appeared to increase under drought when compared to irrigated conditions. Overall, these data indicate that the relative decline in tomato fresh weight from weeds was actually greater under drought, and that the relative crop losses (per unit of weed biomass) actually declined as water availability increased. From a management standpoint, these data suggest that if drought occurrences do increase in the Mediterranean region with climate change, there may be a greater need for complete and thorough weed control for this production system.