Bruce Auld

Vegetable oil suspension emulsions reduce dew dependence of a mycoherbicide

Abstract The use of vegetable oil suspension emulsions in controlled-environment conditions to reduce dew dependence in the mycoherbicide based on the fungus Colletotrichum orbiculare to control the weed Xanthium spinosum is reported. Spores of C. orbiculare were dried with kaolin to produce a powder containing 1 × 109 spores g−1. The dried powder was mixed with one of several commercial vegetable oil products (canola, peanut, safflower, soybean, corn and sunflower) and an emulsifying agent Latron (modified phthalic glycerol alkyd resin) to give a final composition of 10% oil, 1% Latron, 89% water and 1 × 106 spores ml−1. The oil suspension emulsions were applied to X. spinosum without dew (50–55% relative humidity) and compared with an aqueous suspension with and without dew. All of the oil formulations were a significant improvement over the aqueous suspension without dew. There were no significant differences between oils, but canola oil appeared to be the most promising.

Managing Alien Plants for Biodiversity Outcomes—the Need for Triage

Abstract Recognition that alien plants pose a significant threat to biodiversity has not always translated into effective management strategies, policy reforms, and systems to establish priorities. Thus, many alien plant management decisions for the protection of biodiversity occur with limited knowledge of what needs to be protected (other than biodiversity in a generalized sense) or the urgency of actions. To rectify this, we have developed a triage system that enables alien plant management decisions to be made based on (1) the urgency of control relative to the degree of threat posed to biodiversity, compared with (2) the likelihood of achieving a successful conservation outcome as a result of alien plant control. This triage system is underpinned by a two-step approach, which identifies the biodiversity at risk and assesses sites to determine priorities for control. This triage system was initially developed to manage the threat posed by bitou bush to native species in New South Wales (NSW), Australia. It has subsequently been improved with the national assessment of lantana in Australia, and the adaptation from a single to multiple alien plant species approach on a regional scale. This triage system identifies nine levels of priority for alien plant management aimed at biodiversity conservation, ranging from immediate, targeted action to limited or no action. The development of this approach has enabled long-term management priorities to be set for widespread alien plants that are unlikely to be eradicated. It also enables control to occur in a coordinated manner for biodiversity conservation at a landscape scale, rather than as a series of individual unconnected short-term actions. Nomenclature: Bitou bush, Chrysanthemoides monilifera (L.) Norl.; lantana, Lantana camara L.

Effect of environmental factors and precursors on oxalic acid production, mycelial biomass and virulence of a potential bioherbicide isolate of Sclerotium rolfsii SC64 produced in liquid culture

Abstract The fungus Sclerotium rolfsii is presently under development as a bioherbicide for broadleaf weed species using fungus-infested substrates as application material in this laboratory. The effect of environmental factors and three precursors (citric acid, ascorbic acid, and sodium succinate) on mycelial growth, oxalic acid production, and virulence by SC64 in liquid culture were investigated. The results showed that for mycelia growth the optimum liquid medium was Modified Richards solution (MRS) among the five tested media, but potato dextrose broth (PDB) produced the maximum oxalic acid production and virulence on detached Solidago canadensis leaves. When PDB was used as the basic medium, the oxalic acid/mycelial dry weight (mg g–1) ratio reached the peak 4 days after inoculation. The optimum temperature for oxalic acid production was at 27°C, but increased mycelial dry weight and virulence were observed at 30°C. The optimum range of initial pH value for oxalic acid accumulation was 4.0–6.0, with the optimal pH 5.0; highest mycelial growth was with an initial pH 3.5–6.0 (optimum pH 5.0) and subsequently pH 3.5–5.5 (maximum at pH 3.5). Both mycelial dry weight and oxalic acid production showed a decreasing trend as a result of the precursor of oxalic acid being added to PDB. Among the three precursors, the greatest decrease in mycelial dry weight, and oxalic acid production was caused by sodium succinate. This clarification of optimal conditions for production of mycelial biomass while insuring high concentrations of oxalic acid and high virulence should be useful for further development of this fungus as biocontrol agent.