Influence of nitrogen rate on the efficacy of herbicides with different modes of action

Abstract

Sønderskov M, Swanton CJ & Kudsk P (2012). Influence of nitrogen rate on the efficacy of herbicides with different modes of action. Weed Research 52, 169–177.SummaryOutdoor pot experiments and field experiments were conducted to examine the influence of nitrogen rate on herbicide efficacy. Growth of unsprayed Tripleurospermum inodorum increased with increasing nitrogen rate in pot experiments; increasing nitrogen also increased the susceptibility to tribenuron‐methyl. An increased susceptibility at high nitrogen rate was also observed for Anagallis arvensis, but in contrast to T. inodorum, growth of unsprayed A. arvensis was unaffected by nitrogen rate. Growth of unsprayed Chenopodium album was also promoted by nitrogen supply. However, no influence of nitrogen rate on herbicide efficacy was evident for C. album with tribenuron‐methyl or ioxynil+bromoxynil in pot experiments. Field experiments with tribenuron‐methyl were conducted on natural populations of C. album in spring barley grown at different nitrogen rates showed similar results. In conclusion, nitrogen rate affected herbicide efficacy for some but not all combinations of weed species and herbicide. Decreased herbicide efficacy was only observed at very low nitrogen rates. The results suggest that the effect of nitrogen rates on herbicide efficacy will be marginal in intensive farming systems with high nitrogen supply, but in low intensity systems, weed patchiness might increase.