Effects of anaerobic soil disinfestation carbon sources on soilborne diseases and weeds of okra and eggplant in Nepal

Soilborne diseases, root-knot nematodes (Meloidogyne spp.), and weeds are the major yield-limiting factors in okra (Abelmoschus esculentus) and eggplant (Solanum melongena) production in Nepal. Anaerobic soil disinfestation (ASD) is a promising technique in developed countries to control soilborne pests, but it has not been tested in many developing countries. Experiments were conducted in the western plain region of Nepal in okra and eggplant from March to July 2016 and October 2016 to April 2017 (eggplant only) to compare locally available carbon sources for efficacy in ASD. Experiments were conducted in a randomized complete block design with three replicates of seven amendments (molasses 2 kg m⁻², rice bran 2 kg m⁻², rice bran 1 kg m⁻² plus molasses 1 kg m⁻², raw goat manure 2 kg m⁻², mustard (Brassica campestris var. toria) cake 1.5 kg m⁻², lentil (Lens esculenta) husks 2 kg m⁻², and berseem clover (Trifolium alexandrinum) leaves 3 kg m⁻²), and a non-amended, uncovered (aerobic) control in the first year. Lentil husks and berseem clover were replaced by wheat bran (2 kg m⁻²) and wheat bran (1 kg m²) plus molasses (1 kg m⁻²) in the second year. Carbon sources were incorporated into soil followed by irrigation to saturation, and plots were covered with white plastic sheeting for 21 days. Significantly lower Fusarium wilt incidence, root-knot disease severity, and weed biomass were observed in ASD-treated eggplant plots compared to the control in 2016; disease, root-knot and weed pressure were low in 2017 and differences were not significant. Root knot disease severity and weed biomass were significantly reduced compared to the control in ASD-treated okra plots, depending on the carbon source used. With the exception of plots amended with molasses (eggplant, 2017) or molasses alone or combined with rice bran (okra), significantly higher fruit yields were observed in ASD-treated plots than in control plots. ASD appears to have great potential in Nepal because of its broad-spectrum impact on multiple soilborne pests and ready availability of inexpensive local inputs.