The objective of this work was to evaluate the influence of post-emergency herbicide application on the photosynthetic activity of two soybean cultivars (M-SOY 7908 RR and M-SOY 8001). A randomized block experimental design was used with four replicates. Treatments consisted of applied herbicide mixtures or herbicides only: lactofen, glyphosate, lactofen + chlorimuron-ethyl, chlorimuron-ethyl + imazethapyr, chlorimuron-ethyl + bentazon, glyphosate + imazethapyr, lactofen + chlorimuron-ethyl + imazethapyr, lactofen + chlorimuron-ethyl + imazethapyr / haloxyfop-methyl. The tests included two control. The evaluations were taken after the application of herbicides at 4; 11; 18; 25 and 32 in the first crop and at 6, 14, 21, 28 and 35 DAA in the second crop. The M-SOY 8001 was susceptible the herbicides application mostly the herbicide mixture lactofen + chlorimuron-ethyl and lactofen + chlorimuron-ethyl + imazethapyr + haloxifop-methyl the herbicides caused reduction in maximum quantum efficiency of PSII (Fv/Fm). However, both varieties were susceptible to the treatments lactofen alone applied and the mixtures lactofen + chlorimuron-ethyl, chlorimuron-ethyl + imazethapyr, lactofen + chlorimuron-ethyl + imazethapyr and lactofen + chlorimuron-ethyl + imazethapyr + haloxifop-methyl with reduction in chlorophyll relative content by portable chlorophyll meter. However, these damages were reversible, disappearing gradually with plant growth.
Chlorophyll; fluorescence; chlorophyll meter
