The use of eucalyptus leaves for weed control in maize-based croppingsystems is proposed. Aqueous extracts of eucalyptus are known to exertphytotoxicity on many weeds and crops, but there is also experimentalevidence of the relative tolerance of maize. Based on in vitro dose-responsebioassays of leaf aqueous extracts, we conducted greenhouse pot experimentstesting incorporated eucalyptus leaves as green manure. The phytotoxiceffects were tested on the germination, establishment and growth of maizeand some representative accompanying weeds, in comparison to the PREherbicide metolachlor. Eucalyptus fresh leaves incorporated into the soil asgreen manure at 1 and 2% w/w reduced the emergence of the dicot weed speciesredroot pigweed and black nightshade. After one month of incorporation, bothdoses reduced aerial biomass >94% two monocot weed species (barnyardgrass+ large crabgrass) with respect to the eucalyptus-free pots, and around 80%for the small seeded dicots. Although the aerial biomass of maize wasreduced by 33%, the final relative yield of maize biomass with respect tothe untreated control increased by 37%. On the assessment of the temporalphytotoxic effects, the reduction of aerial biomass in maize could beovercome by adopting a relay-planting of maize after 12 to 15 days fromeucalyptus incorporation. Our results constitute evidence that theincorporation of E. globulus residues to soil could be afeasible practice to reduce the reliance on synthetic herbicides inmaize-based cropping systems.

Cover crops can provide many benefits in agroecosystems, including theopportunity for improved weed control. However, the weed suppressivepotential of cover crops may depend on the species (or mixture of species)chosen, and the method of cover crop termination and residue management. Theobjective of this study was to determine the effects of cover crop mixtureand mechanical termination method on weed biomass and density, and relativecrop yield in an organic cropping system. A field experiment was conductedfrom 2009 to 2011 near Mead, NE, where spring-sown mixtures of two, four,six, and eight cover crop species were included in a sunflower–soybean–corncrop rotation. Cover crops were planted in late March, terminated in lateMay using a field disk or sweep plow undercutter, and main crops wereplanted within 1 wk of termination. Terminating cover crops with theundercutter consistently reduced early-season grass weed biomass, whereastermination with the field disk typically stimulated grass weed biomassrelative to a no cover crop control (NC). The effects of cover crop mixturewere not evident in 2009, but the combination of the undercutter and theeight-species mixture reduced early-season weed biomass by 48% relative tothe NC treatment in 2010. Cover crops provided less weed control in 2011,where only the combination of the undercutter and the two-species mixturereduced weed biomass (by 31%) relative to the NC treatment. Termination withthe undercutter resulted in relative yield increases of 16.6 and 22.7% incorn and soybean, respectively. In contrast, termination with the field diskresulted in a relative yield reduction of 13.6% in soybean. The dominantinfluence of termination method highlights the importance of appropriatecover crop residue management in maximizing potential agronomic benefitsassociated with cover crops.