Impact assessment of residual soil-applied pre-emergence herbicides on the incidence of soybean seedling diseases under field conditions

A multi-environmental field study was conducted in 2017 and 2018 in Nebraska to investigate potential interactions between soybean seedling diseases and soil-applied residual pre-emergence (PRE) herbicides. Experiments were established from mid-May to early June in fine-textured, poorly drained soils with a history of seedling establishment problems. PRE herbicides consisted of chlorimuron-ethyl, flumioxazin, metribuzin, saflufenacil, and sulfentrazone applied at labeled rates, in addition to non-treated control. Assessments included soybean injury, seedling root lesion severity (DSI), plant height, population, biomass, and yield. Additionally, symptomatic seedling roots were sampled for fungal and oomycete organisms to expand comprehension of potential biotic associations. Greater soybean injury and reduced root biomass were observed in two distinctive environments following PPO-inhibiting PRE herbicide applications. Exceptionally in one environment, where DSI seemed (P = 0.07) lower for metribuzin in comparison to saflufenacil, PRE herbicides did not affect seedling root rot severity and no yield differences occurred among treatments. Community composition depicting Fusarium, Phytophthora, Pythium, and Rhizoctonia genera varied considerably across environments (P < 0.001) and DSI classes (P = 0.002), representing distinctive ecological environments under investigation. Phytophthora structured a large portion (>40%) of the total primary pathogenic isolates recovered in the highest DSI environment, whereas Pythium frequency ranged from 4.6% to 22% across all surveyed environments, and Rhizoctonia recovery was low (<10.3%) and sporadic. Across environments with varying DSI and soilborne pathogen composition, results indicated a lack of consistent interaction between soil-applied residual PRE herbicides and the incidence of soybean seedling diseases in optimal to delayed planting situations.