Evaluation of a pre-formulated post-emergence herbicide mixture of topramezone and dicamba on annual weeds and Bermuda grass in maize in a sub-tropical agro-ecology

Weed infestation is one of the major causes of low maize grain yield in sub-Saharan Africa (SSA). The perennial grass weed, Cynodon dactylon (L.) Pers., is one of the most problematic weeds in maize in SSA. A pre-formulated post-emergence herbicide mixture (50 g a.i. topramezone litre(−1) + 160 g a.i. dicamba litre(−1)), sold under the trade name Stellar-Star(®), was evaluated for C. dactylon and general weed control in the 2013/14 and 2014/15 season. The experiment was laid out as a randomized complete block design (RCBD) with six treatments replicated thrice, namely; weedy control, hoe weeding at 3 and 6 weeks after crop emergence (WACE), a label recommended dose of Stellar-Star at 3 WACE, a reduced Stellar-Star dose (75% of label dose) at 3 WACE, a double dose of Stellar-Star split applied at 3 and 6 WACE and a tank mix of label doses of Stellar-Star + Atrazine applied at 3 WACE. The Stellar-Star herbicide treatments did not significantly (P > 0.05) affect C. dactylon density at 5 WACE but significantly reduced (P < 0.001) its density at 10 WACE. The Stellar-Star herbicide treatments significantly reduced (P < 0.001) weed biomass compared to the weedy-check at 5 and 10 WACE in both seasons. The Stellar-Star double dose split application and the Stellar-Star Atrazine tank mix were most effective in controlling C.dactylon (90–97% control) followed by the Stellar-Star label dose and Stellar-Star reduced dose (75%–88% control), however, the results of this study suggest that the Stellar-Star Atrazine tank mix provided the most effective early season and overall weed control and resulted in the highest yield, rainfall use efficiency (RUE) and gross margin and is recommended.