Influence of light intensity on the effectiveness of 2,4-D and dicamba in controlling Euphorbia heterophylla L.

Euphorbia heterophylla L. is a harmful weed in crops. Its phenotypic plasticity under varying light conditions affects morphophysiological traits and herbicide sensitivity. Two independent experiments were conducted in a 2 x 6 factorial design under two environments (full sun and 73% shading) and six herbicide doses. Dicamba was applied at 0, 120, 240, 360, 480, and 720 g a.e. ha−1, and 2,4-D at 0, 168, 335, 670, 1005, and 1340 g a.e. ha−1, 50 days after sowing. Full-sun plants showed 83% higher wax content than shaded plants. Shaded plants were more sensitive to 2,4-D at lower doses and to dicamba. Increased applications of 2,4-D and dicamba decreased starch reserves and increased soluble sugars, with distinct responses between environments. Shaded plants showed lower starch accumulation, regardless of herbicide or dose. Shading and herbicide application reduced electron transport rate, whereas increasing herbicide doses decreased intercellular spaces under both conditions. E. heterophylla exhibits morphoanatomical, physiological, and biochemical plasticity in response to light, modulating its sensitivity to 2,4-D and dicamba. Shaded plants required 319.3 g a.e. ha−1 of 2,4-D for excellent control, compared with 554.8 g a.e. ha−1 under full sun. Dicamba provided effective control only under shading at 720 g a.e. ha−1.