Effect of sub-lethal doses of 2,4-D sodium salt on physiology and seed production potential of wheat and associated dicotyledonous weeds

A field experiment was conducted in Rabi 2016–17 and 2017–18 to assess the effect of 2,4-D sodium salt at 5, 10, 20, 40 and 50 g/ha along with the recommended dose of 500 g/ha on wheat and associated dicotyledonous weeds (Medicago denticulata and Rumex dentatus). Foliar applied 2,4-D in the range of 5–20 g/ha increased the chlorophyll content index (CCI) and chlorophyll fluorescence (Fv/Fm) values in wheat as compared to control, demonstrating biphasic dose response (hormetic effect) of this auxinic herbicide. But the stimulatory effect of 2,4-D at low doses was observed only upto flag leaf stage of crop. Grain and straw yield of wheat was not boosted significantly by the low doses of 2,4-D, indicating that growth stimulation by sub-toxic doses of 2,4-D was not sustained over time. The foliar application of 2,4-D at ultra-low doses of 5–50 g/ha did not exert hormetic effect in R. dentatus and M. denticulata as application of different doses of 2,4-D led to a reduction in seed production potential of these weeds.