This research was conducted to evaluate the possibility of multiple resistances to ACCase, ALS and carotene synthesis inhibiting herbicides in one ACCase-resistant biotype of crab-grass (Digitaria ciliaris). The experiment was conducted in a greenhouse, using two crab-grass biotypes: one resistant (R) and another susceptible (S) to ACCase inhibiting herbicides. The experimental design adopted was randomized blocks, with four replicates. Eleven herbicides were used: fluazifop-p-butyl, haloxyfop-r-methyl, propaquizafop, sethoxydim, tepraloxydim, clethodim, fenoxaprop + clethodim, imazethapyr, nicosulfuron, iodosulfuron + foramsulfuron and mesotrione. For each herbicide, the treatments resulted from a factorial combination between two biotypes of crabgrass and 10 rates (0.0D; 0.016D; 0.03D; 0.06D; 0.25D; 0.5D; 1.0D; 2.0D; 4.0D and 16.0D); where D is the recommended rate for each product. The herbicides were applied over crabgrass plants at the 3-4 leaf development stages. Percent control was evaluated 28 days after application (DAA). Biotype R was confirmed as resistant to ACCase inhibiting herbicides (chemical groups of ariloxifenoxipropionates and cyclohexanodiones) with variable levels of cross-resistance. Also, biotype R was satisfactorily controlled by the field rates of all the alternative herbicides applied (sulfonilureas, imidazolinones and inhibitors of carotene synthesis), excluding the hypothesis of multiple resistance in this crab-grass biotype.
cross-resistance; multiple resistances; chemical control
