Weed and yield of different field pea seed rates and carryover effect of ALS inhibitor herbicides applied in preceding wheat crop

Intercropping with greater pulse seeding rates for weed mitigation could increase growers yield returns and potentially reduce weed resistance, caused by frequent herbicide applications. In 2021, a split-split plot experiment in North Star, Alberta was sown to wheat (Triticum aestivum L.) in two fields; half the plots were sprayed with Thifensulfuron-methyl + tribenuron-methyl at 29.65 g.a.i.ha⁻¹ (9.89 + 4.94 respectively) at flag leaf with other half left untreated. In the following spring (2022), field pea (Pisum sativum L.) was sown at 0.5X, 1X and 1.5X seeding rate (101, 202 and 303 kgha⁻¹, respectively) with either ryegrass (Lolium multiflorum L.) or rye (Secale cereale L.) at 5.6 and 19.1 kgha⁻¹, barley (Hordeum vulgare L.) or oat (Avena fatua L.) at 33.7 kgha⁻¹, plus monocrop control. Objectives were to a) identify most weed suppressive intercrop, and b) how companion crops affected pea seeding rates. Herbicide sprayed plots had less weeds compared to unsprayed despite cropping system adopted and rye was best companion crop to reduce weeds. Rye-pea (1.11) or ryegrass-pea (0.98) land equivalent ratio (LER) were greater than oat-pea (0.75). Cereal Agressivity (A) (2.64X10⁻³ and 2.18X10⁻² in oat and barley) and actual yield loss (AYL) (3.06 in oat, 0,39 in barley) was greater than pea (−2.67X10⁻³, −2.29X10⁻² for A and 2.95, 0.73 for AYL in oat and barley respectively), inversely to competitive ratio (CR) (0.07, 2.60 in oat and pea; 0.25, 0.63 in barley and pea). More pea stands decreased cereal CR (0.36,0.11 and 0.05 at 0.5X, 1X and 1.5X pea seeding rates) and AYL (1.56, 1.41 and 0.59 for same pea seeding rates). Overall, a) increasing pea seeding rates reduce weeds and increase competitivity towards cereals, and b) despite rye being more suppressing, barley and oat promote pea yields with less area likewise. This study demonstrated the variety of IWM strategies possible in Northern Alberta.