Integrating the organic arsenal for weed control in field pea and lentil

Organic weed management in pulse crops is challenging due to their uncompetitive nature in the presence of weeds. Since the use of synthetic herbicides is prohibited in organic production, growers tend to rely heavily on mechanical and cultural weed control methods. To our knowledge, no previous research has directly compared the following in-crop mechanical weed control (MWC) methods: rotary hoe (RH), harrow (H) and inter-row cultivation (IT) combined with the cultural practice of increased crop seeding rate (SR) in organic pulse crops. The objective of this research was to determine the effect of mechanical weed control (RH, H and IT) and crop (SR) alone and in combination on weed suppression and yield in organically grown field pea (Pisum sativum L.) and lentil (Lens culinaris L.). The study was conducted in organically managed cropping systems in Saskatchewan, Canada in 2016 and 2017. Mechanical weed control methods including RH, H and IT were applied in a factorial arrangement with normal and increased SR in organically grown field pea (1 and 1.5X) and lentil (1 and 2X). Averaged over all site-years, all MWC treatments resulted in similar field pea yield increases ranging from 38% to 50%. Paired and multiple treatments reduced weed biomass in field pea by 73% to 86%. Increasing field pea SR 1.5X did not significantly improve weed control, but it did increase field pea yield by 13%. The combination of RH-IT resulted in 40% higher lentil grain yield. Increasing lentil SR to 2X the normal rate resulted in a 23% increase in yield, while weed biomass was reduced by 16%. Combinations of RH-IT and RH-H-IT in lentil resulted in a 76% and 79% decline in weed biomass, respectively. Treatments including RH, provided the greatest spectrum of weed control spectrum in both crops as on average they controlled more than 80% of the green foxtail (Setaria viridis L.), 60% of the wild mustard (Sinapis arvense L.), and 86% of the lambsquarters (Chenopodium album L.). Use of MWC did not provide robust control of redroot pigweed (Amaranthus retroflexus L.) or wild buckwheat (Polygonum convolvulus L.) and stimulated emergence of stinkweed (Thlaspi arvense L.). Our study suggests that effective weed suppression and greater yield can be achieved in an organic crop production system when MWC methods are paired with cultural practice of increased crop SR.