Managing copper inputs to viticultural soils for the protection of soil fertility

Copper-based fungicides have been used in vineyards throughout the world since the end of the 19th century protect against fungal diseases. However, this use results in an accumulation of copper (Cu) in surface soils which may cause negative effects to soil biota (e.g. earthworms, micro-organisms), and have implications for the long-term fertility and sustainability of these agricultural soils. Due to concerns around the environmental risks, there are societal and regulatory pressures to enforce restrictions on the use of Cu-based fungicides. Such regulatory restrictions have come into force in some jurisdictions, for instance as a requirement of re- the European Commission require member states to take steps to ensure that the rate and number of Cu-based fungicide applications are the minimum to achieve desired effects. However, assessment of the risks posed by Cu-based fungicide residues in vineyard soils has received relatively little attention in Australia. As such, scientific information is needed to characterise the risks currently posed by Cu-based fungicide residues in Australian vineyard soils and to inform decisions on the future management of Cu-based fungicides. These decisions need to consider the environmental risks of replacement chemicals as they may not necessarily pose a lower risk. Unfortunately, there is relatively little information on the environmental fate and ecotoxicological effects of alternative synthetic organic fungicide compounds. This project aimed to determine the risks that Cu-based fungicide residues currently pose to soil organisms in Australian vineyards, and how these risks vary across different viticultural regions. It also aimed to contribute towards a relative risk assessment of synthetic organic compounds available for use as alternatives to Cu-based fungicides. Initial experimental work sought to characterise the environmental availability of Cu-based fungicide residues in vineyard soils from 10 different viticultural regions of Australia. The availability of the Cu was found to be relatively low (< 0.5 % of total Cu in the majority of vineyard soils), and influenced by the total Cu concentration of the soil and soil properties influencing cation exchange processes and capacity for soil to adsorb Cu (i.e. pH, clay, exchangeable K, silt, CaCO3). Published data on total Cu concentrations and new information on concentrations of available Cu in Australian vineyards soils generated by this research were used to indicate exposure concentrations to soil organisms which identified likely risks to soil organisms. The second phase of this project involved the incubation of ‘real’ field collected soils from three different regions of Australia to determine the ecotoxicological effects of long-term exposure to Cu-based fungicide residues to enzyme activities (as sensitive indicators of microbial activity). At the concentrations of Cu present in the studied soils (i.e. 90 % less than 115 mg/kg total Cu) the results suggested that enzyme activities were being driven predominately by physical-chemical soil properties (i.e. organic C, pH) with little evidence of adverse effects due to Cu. However, there were some indications that Cu was disrupting microbial mediated phosphorus processes in the soils. Whilst not appearing to directly affect soil microbial activity it was thought that this persistent Cu stress may affect the susceptibility of microbial activity to secondary stressors such as an additional heat stress. Experimental work to assess this found that at the concentrations of Cu typically reported in Australian vineyard soils, Cu stress is unlikely to cause lasting alterations to the susceptibility of phosphomonoesterase and urease following a heat disturbance. Globally there are societal and regulatory pressures to move towards restrictions on Cu-based fungicide use. As such, there is likely to be an increase in the use of alternative synthetic organic fungicide compounds. Laboratory experiments suggested that the alternative fungicides, captan and trifloxystrobin, are likely to pose a lower long-term risk to soil microbial activity compared with Cu-based fungicides. However, results from a study in a horticultural production catchment suggest that the use of synthetic organic fungicide compounds may pose a risk to aquatic ecosystems. Although, comparative analysis suggests that on the whole, the use of pthlamide, dithiocarbamate, strobilurin and triazole fungicides over Cu-based fungicides may result in decreased long-term risks to terrestrial and aquatic ecosystems. This project has generated new information on the environmental risks of Cu-based and alternative fungicide compounds which viticultural industries in Australia can use for environmental reporting, benchmarking against viticultural/wine industries in other countries, and formulating evidence-based policy decisions on the future management of Cu-based fungicides. On the whole the evidence suggests that Cu-based fungicide residues are currently unlikely to pose a significant risk to soil organisms in Australian vineyard soils. However, there are indicators that continued applications of Cu-based fungicides may well have implications on the use of impacted land for sustainable agricultural production. Regardless of the actual risks posed there remain societal and regulatory pressures to introduce restrictions on the use of Cu-based fungicides. The challenge is now for the industry to formulate appropriate plans to reduce the risks associated with Cu-based fungicide use, and this should be the focus of future research and development. This should expand on the relative risk assessment of alternative fungicide compounds commenced in this project