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

Abstract

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 a non-treated control. Assessments included soybean injury, seedling root lesion severity (DSI), plant height, population, biomass, and yield. Symptomatic seedling roots were sampled for fungal and oomycete organisms to expand understanding of potential biotic associations. Greater soybean injury and reduced root biomass were observed in two distinctive environments following PPO-inhibiting PRE herbicide applications. In one environment, DSI was slightly lower for metribuzin compared to saflufenacil (P = 0.07), but PRE herbicides did not affect seedling root rot severity and no yield differences occurred among treatments. Community composition of Fusarium, Phytophthora, Pythium, and Rhizoctonia varied considerably across environments (P < 0.001) and DSI classes (P = 0.002), representing distinctive ecological conditions. Phytophthora structured a large portion (>40%) of primary pathogenic isolates in the highest DSI environment, while Pythium frequency ranged from 4.6% to 22%, and Rhizoctonia recovery was low (<10.3%) and sporadic. Across environments with varying DSI and pathogen composition, results indicated a lack of consistent interaction between soil-applied residual PRE herbicides and soybean seedling disease incidence.