Phytotoxicity effects of Topramezone and Dicamba herbicide on selected legumes

Weeds in agriculture are responsible for yield reduction and poor crop quality if not controlled. In maize production, new user-friendly herbicides are being adopted by smallholder farmers. Stellar star whose active ingredients are Topramezone and Dicamba is a selective, systemic post-emergence herbicide used in maize. This poses a threat to crop rotation, especially legumes, due to residual effects. Therefore, the study was carried out to evaluate the phytotoxicity effect of Topramezone and Dicamba herbicide on selected legumes. The trials were conducted in the field and greenhouse. Topramezone and Dicamba herbicide was applied at 4 rates (0, 1.0, 2.0 and 4.0 L ha-1) while legumes were planted at 0, 30, 60, 90 and 120 days residual period. The experimental designs used were CRD for the greenhouse trial and split-split plot design for the field experiment, replicated three and two times respectively. Phytotoxicity effects on legumes were highest at 0, 30 and 60 days residual periods. The coefficient of determination (R2) indicated 96-100% variation in the relationship between days and plant stand count. 4 L ha-1 had the worst average phytotoxicity score of 98%, with control having the lowest at 0%. Results showed whitish, greyish, pale germinated plants which mostly dried after 3 to 5 days. There were highly significant differences (p ≤ 0.01) amongst the treatment means for all parameters.  This means that within 120 days residual period, legumes under study should not be rotated with maize as the herbicide has phytotoxicity effects both at varying application rates and residual period.