Metarhizium brunneum is a highly effective entomopathogenic fungus that also functions as a plant biostimulant. It can act as both an endophyte and rhizosphere colonizer; however, the mechanisms driving biostimulation are multifactorial. In this work, oilseed rape (Brassica napus) seeds were grown in composts treated with different concentrations of M. brunneum strains ARSEF 4556 or V275, or the M. brunneum-derived volatile organic compounds 1-octen-3-ol and 3-octanone. Biostimulation efficacy was found to be strongly dose dependent. Concentrations of 1 × 10⁶ conidia g⁻¹ compost were found to be most effective for the M. brunneum, whereas dosages of 1 µL 100 g⁻¹ compost were found to be efficacious for the volatiles. These optimized doses were assessed individually and in combined formulations with a hydrogel against oilseed rape (Brassica napus), sitka spruce (Picea sitchensis), maize (Zea mays) and strawberry (Fragaria annanassa). Both volatile compounds were highly effective biostimulants and were found to increase in biostimulatory efficiency when combined with M. brunneum conidia. Hydrogels were not found to interact with the growth process and may offer avenues for novel formulation technologies. This study demonstrates that Metarhizium-derived volatile organic compounds are actively involved in plant growth promotion and have potential for use in novel formulations to increase the growth of a wide range of commercially relevant crops.

In order to evaluate the long-term effect of the new fumigant DMDS and its potential to be a part of IPM of root-knot nematodes, a two-year experiment was conducted on cucumber in a greenhouse in Bulgaria. In the first year, DMDS was applied in comparison with farmer nematicide strategy and untreated control in the first cucumber crop. After two consequent catch crops—lettuce in the winter period—a second cucumber crop followed in spring–summer. In this crop, the DMDS effect was studied with no treatment and was integrated into the post-planting strategy with Trichoderma spp. and garlic extract at plots previously treated with DMDS. The effect of DMDS was followed until 450 days after fumigation. Nematocidal efficacy of DMDS was 96% and the yield increased 65.5% in the first cucumber crop, and 80% and 100% in the second cucumber crop, respectively, when nothing was done or a combined strategy with Trichoderma spp. and garlic extract was followed. The DMDS effect on 44 non-target soil nematode genera was also followed. The negative impact of the fumigation was limited in time as non-target nematode communities regained previous crop levels in five months during our study. Therefore, DMDS can be properly included in soil IPM programmes and appears very promising for the protected crop industry in Europe.