Bean cultivar mixture allows reduced herbicide dose while maintaining high yield: A step towards more eco-friendly weed management

Abstract Integrated weed control methods are increasingly demanded to maintain high yield while alleviating negative environmental side effects of control measures. Five field experiments were conducted during 2015–2017 at three locations in Iran to determine the advantage of exploiting enhanced competitive ability of bean (Phaseolus vulgaris L.) via cultivar mixture to reduce herbicide dose. For all experiments, the experimental design was split-plot in randomized complete block with four replications. Main plots were assigned to the factor "herbicide dose" with 5 levels between 0 and 100 % of recommended dose and subplots comprised monoculture of a stand growth type cultivar (STAND), monoculture of a climbing growth type cultivar (CLIMB) and the substitutive (50 % STAND/50 % CLIMB) cultivar mixture (MIXCR). Without herbicide application, the yield of STAND, CLIMB and MIXCR was estimated at 588, 1026, and 1637 kg ha−1, and the corresponding weed biomass (W0) at 388, 215, and 239 g m-2, respectively. The herbicide dose to decrease W0 by 50 % (ed50) was estimated as 69 % of the recommended dose for STAND, while it was 53 and 45 % for CLIMB and MIXCR, respectively. Herbicide application at full rate increased the average yield of STAND by 2610 kg ha−1, but 1115 and 1532 kg ha-1 for CLIMB and MIXCR, respectively. Potential yield of CLIMB at full herbicide rate application was 2141 kg ha−1, while STAND and MIXCR showed statistically the same potential of producing 3198 and 3169 kg h−1 bean yield. However, MIXCR could achieve its potential yield at half of the recommended dose. Relative yield total (RYT) was lower than or equal to one at 75 % and 100 % of the recommended dose, but with decreasing herbicide dose to 50 or 25 % RYT raised to 1.2. Careful selection of cultivars for growing in mixture that combines strong competitor with high yield cultivars is crucial to achieve potential yield with less dependence on herbicides. As we could show for bean, this will help to overcome conflicting management objectives to reach both environmental and economic goals in weed control and crop production.