Effect of Tomato Seed Vigor on the Early Competition with Green Foxtail (Setaria viridis) and Jimsonweed (Datura stramonium)

Direct-seeded industrial tomato (Solanum lycopersicum L.) systems are highly vulnerable to early-season interference, yet the role of seed vigor as a competitive determinant remains under-quantified. This study evaluated the performance of high-vigor (HV; 91% germination) and accelerated-aged low-vigor (LV; 60% germination) tomato seeds against two weeds: green foxtail (Setaria viridis) and jimsonweed (Datura stramonium). While mean emergence timing was statistically comparable between HV and LV cohorts (6.0 vs. 7.2 days), LV seedlings entered the post-emergence phase with a numerical deficit in initial seedling dry weight (7.1 mg vs. 8.5 mg for HV; difference not statistically significant), suggesting a potential early competitive disadvantage. In replacement series experiments, HV tomatoes maintained stable leaf and root biomass within the 0.76–1.24 relative yield (RY) confidence interval when competing with jimsonweed. In contrast, LV plants were significantly suppressed at low weed proportions (25%), where root RY dipped below the 0.76 threshold. Against the aggressive below-ground strategy of S. viridis (which produced ~1200 mg of root mass by 40 DAE), LV tomato root RY collapsed to 0.10–0.15, whereas HV plants maintained significantly higher niche occupancy. Physical separation of above- and below-ground competition confirmed that HV seeds provide a “physiological buffer”; specifically, in below-ground treatments, HV plants achieved a root mass of 0.25 g/plant compared to only 0.15 g/plant for LV plants. These results identify seed vigor as a primary driver of the “priority effect” and suggest that high-vigor lots are essential for Integrated Weed Management (IWM) strategies to mitigate early-season resource pre-emption. These findings suggest that seed vigor assessment should be integrated into seed quality standards for direct-seeded tomato systems as a component of Integrated Weed Management. Future field-based studies are needed to validate these greenhouse findings under variable agronomic conditions.