In order to evaluate the effects of nightshade coexistence on processing tomato yield, hybrid Heinz 9992, an experiment was carried out consisting of two sets of treatments: in the first set, the crop was kept weed free (60 thousands plants ha-1) from transplanting to 15; 30; 45; 60; 75; 90; 105 days and 120 (harvest) days after transplanting (DAT); while in the second set, the crop was kept in competition with the nightshade from transplanting until the same DAT described for the set of treatments. A randomized block design trial, with three replications and four-row plots was used. Height, leaf area, and aerial part dry matter of nightshade was obtained out of 10-plant samples. Nightshade leaf area increased until 75 days of tomato coexistence (1,588 dm² plant-1); height until 60 days of coexistence (85 cm), and the leaf dry biomass until 120 days of coexistence (31.7 g plant-1). The highest (108.6 tons ha-1 or 87.6 % of total production) and lowest (14.2 tons ha-1 or 59%) ripe tomato yields were observed when the coexistence between tomato and nightshade occurred only in the first 15 days or in the whole crop cycle, respectively. In these treatments, the average ripe fruit weights were 58.7 and 38.0 g, respectively. Each cm² of increase in the nightshade leaf area caused a reduction of 0.04 tons ha-1 (R² = 0.90) on the ripe tomato yield; each cm of increase in the nightshade height reduced the ripe tomato yield in 0.82 tons ha-1 (R²=0.78); and each gram of increase in the nightshade aerial part dry matter reduced the ripe tomato yield in 2.84 tons ha-1 (R²=0.97). The period before interference, allowing up to 5% reduction in tomato yield, was 27 DAT; the total period for preventing interference was 46 DAT; and the critical period for preventing interference was between 27 and 46 DAT.
Lycopersicon esculentum; Solanum americanum; weed competition; coexistence crop-weed
