Control of Digitaria insularis (L.) Fedde in eucalyptus forests: shading increases sensitivity to glyphosate applied alone and in a mixture with carfentrazone-ethyl

Abstract

Shading, the predominant condition in most of the eucalyptus cultivation cycle, causes changes in the morphological and physiological weed's characteristics, which can alter their responses to glyphosate and carfentrazone-ethyl, important herbicides for the crop. The objective was to evaluate the influence of light on the efficiency of glyphosate and carfentrazone-ethyl used alone and in a mixture in Digitaria insularis control, a priority pest in the crop. The experiment was carried out in a 3 × 6 factorial scheme. The first factor corresponded to 3 cultivation environments (full sunlight, 45 and 63% shading) and the second factor to doses of glyphosate and carfentrazone-ethyl applied isolated (1920 and 40 g ai ha−1) and mixed (1536 + 8; 1152 + 16; 768 + 24 and 384 + 32 g ai ha−1), respectively. Shading increased D. insularis sensitivity to glyphosate alone and in a mixture with carfentrazone-ethyl. In shading, the glyphosate application alone at a dose of 1920 g ha−1 and in a mixture with carfentrazone-ethyl at doses of 1536 + 8 and 1152 + 16 g ha−1 were efficient in D. insularis control. In the environment of 63% shading, the dose of 768 + 24 g ha−1 was also efficient in this species control. None of the doses were effective in controlling D. insularis in full sunlight. Isolated carfentrazone-ethyl was inefficient in controlling D. insularis, regardless of the growth environment. Shading increases the quantum yield of photosystem II and reduces the electron transport rate, photosynthetic rate, stomatal conductance, and transpiration rate of D. insularis. In shady environments, it is possible to control D. insularis with lower glyphosate doses, used alone and mixed with carfentrazone-ethyl.