Managing soilborne diseases of vegetable crops with a pre-plant soil or substrate amendment of a corn distillation product1

Abstract

The efficacy of condensed distiller's solubles (CDS), a co-product of ethanol production from corn, rich in organic matter, and high in carbon to nitrogen ratio, was tested as a pre-plant amendment against Verticillium wilt of eggplant and potato scab in potato soils from commercial fields and against damping-off diseases of radish and cucumber seedlings in a peat-based mix and muck soil. Eggplants grown in a potato soil amended with CDS (1% mass/mass) showed less Verticillium wilt and increased fresh (37–54%) and dry (31–45%) plant biomass compared to the control in the greenhouse. In a potato soil with medium levels of disease, CDS (1 or 2%) increased the percentage of marketable tubers by 116% under greenhouse, 119% under micro-plot and 75% under field conditions. In the growth room, CDS (1, 2, and 4%) amendment to a peat-based mix infested with Rhizoctonia solani 1 week before planting seeds improved the percentage of healthy radish seedlings (22–72% healthy seedlings compared to 2% in the control). Levels of disease suppression increased with the incubation time prior to planting. Disease control effect of CDS was not consistent between different batches of peat-based mix. In a non-suppressive batch of peat-based mix, disease suppression by CDS was enhanced by a bio-control agent, Trichoderma hamatum 382. In muck soil from a commercial field naturally-infested with Pythium spp., CDS (0.25, 0.5, and 1%) provided protection of cucumber seedlings from damping-off immediately after incorporation, but the maximum protection was seen after 1 week with all three rates. The number of total bacteria was enhanced in the CDS-amended muck soil. In the micro-plots, CDS (0.5 and 1%) as an amendment to muck soil 2 weeks before planting improved the percentage of healthy cucumber seedlings and fresh plant weight compared to the control. CDS is not toxic to the pathogens and disease suppression is believed to be due to biological activity stimulated by CDS in the substrate.