Responses of Coffea arabica to sublethal doses of the herbicides glyphosate and metsulfuron-methyl

Hormesis, a biphasic dose‒response characterized by low-dose stimulation and high-dose inhibition, was investigated in Coffea arabica seedlings treated with subdoses of glyphosate (0, 25, 50, 75, 100, 125, and 150 g a.e. ha−1) and metsulfuron-methyl (0, 0.193, 0.348, 0.450, 0.600, 0.750, and 0.970 g a.i. ha−1). For each herbicide, a completely randomized design (CRD) was used, and treatments were applied 10 days after transplanting. Growth was assessed at 15, 30, 45, and 60 days. Glyphosate at 25–75 g a.e. ha−1 increased seedling height, whereas 150 g a.e. ha−1 reduced seedling height by 50%. Shoot dry mass declined at ≥ 75 g a.e. ha−1, and leaf area declined at 125–150 g a.e. ha−1. Metsulfuron-methyl stimulated the height at 0.193–0.750 g a.i. ha−1 but inhibited it at 0.970 g a.i. ha−1. Only the lowest dose increased the leaf area and dry mass. These findings reveal that minimal herbicide exposure can positively modulate coffee seedling development, highlighting its potential agronomic relevance.