The efficiency of two Trichogramma species as biocontrol agents against the European corn borer (ECB) Ostrinia nubilalis (Lepidoptera: Crambidae) was investigated under field conditions. Five inundative releases of Trichogramma ostriniae and T. brassicae (Hymenoptera: Trichogrammatidae) were done in sweet corn plots. Ostrinia nubilalis sentinel egg masses were placed on corn plants in order to compare the efficiency of the two Trichogramma species. The parasitism rate of O. nubilalis egg masses by T. ostriniae was 13% higher than egg masses parasitized by T. brassicae. Likewise, the percentage of eggs parasitized per mass by T. ostriniae was significantly higher following two of the five releases. Attacked egg masses showed an average of 29% of eggs parasitized by T. ostriniae, versus 14% of eggs parasitized by T. brassicae. The rate of parasitoid emergence from sentinel egg masses was also significantly higher for T. ostriniae than for T. brassicae. Damages to plants due to ECB did not differ significantly in presence of the two parasitoid species. However, plants in plots receiving parasitoids showed less damage than plants in control plots. Overall, T. ostriniae was clearly more efficient than T. brassicae to parasitized egg masses of O. nubilalis in sweet corn.
Ten products, commercially available as biostimulants or reported for their biostimulating properties, were tested under conventional and organic growing systems for their effects on mustard microgreens (Brassica juncea) grown in presence of abiotic (salt) or biotic (Pythium ultimum) stress. Drench application of wollastonite (calcium silicate) significantly improved the germination rate of mustard seeds sown in a substrate inoculated with P. ultimum in conventional growing system exclusively. In both growing systems, no significant effect of biostimulants was observed on the dry biomass or the proportion of healthy microgreens grown in presence of P. ultimum. None of the biostimulants significantly increased the germination rate of seeds exposed to a salinity stress in both growing systems while humic acid, triacontanol, chitosan, and Bacillus subtilis PTB185 significantly decreased the germination rate of seeds exposed to 40, 80 or 120 mM NaCl L-1 under conventional or organic management. Seed treatment with Trichoderma harzianum T-22 and humic acid resulted in microgreens with a significantly higher dry biomass when subjected to 40 and 80 mM NaCl L-1 under conventional and organic management, respectively. The study showed that the effects of the biostimulants vary from beneficial to detrimental and that plant response to biostimulants is influenced by the cultivation conditions.
Organic soils are an important resource for vegetable crops. However, these crops are very demanding in terms of pest control, fertilization and tillage. Combined with organic soil subsidence, current practices threaten the sustainability of this resource. In this study, we test the potential of Sunn hemp ( Crotalaria juncea) ) as a green manure to control populations of plant-parasitic nematodes and as a carbon input to the soil. Incorporating Sunn hemp resulted in a tenfold reduction in populations of the northern root-knot nematode ( Meloidogyne hapla) ) and a significant increase in carrot yields the following year. However, no significant effect was observed on the root-lesion nematode, Pratylenchus penetrans. .
