The use of pre-emergence herbicides under plastic mulch is an effective strategy for weed control in plasticulture beds in vegetable production systems. S-metolachlor is a pre-emergence herbicide labeled for application in soil prior to laying plastic mulch in tomato production in Florida. However, the risk of crop injury has limited its adoption in plasticulture systems, highlighting the need for crop-safe herbicide application approaches. This study aimed to evaluate the potential of herbicide safeners including chemical seed treatments and activated charcoal in mitigating tomato transplant injury from herbicides such as S-metolachlor. A greenhouse experiment was conducted at the Southwest Florida Research and Education Center (SWFREC) in Immokalee, FL, across two trials: March–June (Trial I) and August–November (Trial II) of 2024. Field soil was collected and used in pots for both trials. Treatments included tomato seed pre-treatments with benoxacor or fenclorim, and transplant root treatments with activated charcoal applied either as a root dip or poured into planting holes. All treated transplants and non-treated controls were grown in S-metolachlor-treated soil. Seed pre-treatment with benoxacor or fenclorim reduced crop injury by over 63% compared to non-treated controls. Activated charcoal applied to transplant roots reduced injury by 40–70% in Trial I and by over 70% in Trial II. Chlorophyll content was consistently higher in safener-treated plants, with activated charcoal increasing levels by more than 16% at 2 weeks after transplanting (WAT) and by 11–20% at 6-WAT. Similarly, benoxacor and fenclorim treatments improved chlorophyll content by 12–19% at 6-WAT. Root biomass in non-treated transplants was reduced by 56–70% due to S-metolachlor exposure. In contrast, both activated charcoal and seed-applied safeners helped preserve root biomass, with benoxacor and fenclorim reducing root weight loss by 65–70% compared to untreated controls. Overall, the results demonstrate that both seed-applied (benoxacor, fenclorim) and root-applied (activated charcoal) safeners are effective in mitigating S-metolachlor injury in tomato transplants and may offer viable strategies for enhancing crop safety in plasticulture-based vegetable production.
