Efficiency of glyphosate and carfentrazone-ethyl in the control of Macroptilium atropurpureum (DC.) Urb. under different light intensities

Variation in environmental conditions, such as light availability, can affect herbicide efficacy by altering leaf morphoanatomy. Accordingly, the aim of the present study was to evaluate the influence of light level and herbicide application on leaf anatomy and herbicide efficacy, using Macroptilium atropurpureum as a model weed species. The experiment involved a factorial design (3 × 4), using three light levels (0, 50, or 70% shadow) and four herbicide treatments (no herbicide, glyphosate, carfentrazone-ethyl, or a combination of glyphosate and carfentrazone-ethyl). When combined, the herbicides were efficient in controlling M. atropurpureum under all light levels. However, when applied independently, the herbicides failed to satisfactorily control plants cultivated in full sunlight, and plants cultivated in shaded environments were more sensitive to glyphosate application than those cultivated in full sunlight. The greater efficacy of the herbicides on plants grown under shaded conditions can likely be attributed to changes in leaf morphoanatomy. Plants grown under restricted light conditions exhibit greater average leaf area, lower trichome density, reduced epicuticular wax deposition, thinner leaves, and lower dry mass accumulation, characteristics which are closely correlated to chemical control. The combination of the herbicides presents an additional effect in the control of M. atropurpureum. Also, changes in leaf anatomy caused by light restriction reduce the tolerance of M. atropurpureum to the herbicides.