What is fungicide resistance?
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Resistance in a fungal pathogen to specific fungicides usually results from the intensive use of fungicides from the same chemical group.
In any fungal population there will be individuals that have a natural resistance or are less susceptible to fungicides, even before any exposure to the new chemistry. Resistance can arise through selection pressure placed upon the fungal population. This allows the resistant strains to thrive at the expense of susceptible strains. Eventually the population shifts to include sufficient resistant fungi, causing a control failure for the chemistry involved.
During the development of dimethomorph in Australia, field trials were conducted on sites where strains of downy mildew had become resistant to metalaxyl (Ridomil®). Conducted in Queensland and Victoria, the trials clearly demonstrated the effectiveness of dimethomorph in the control of metalaxyl resistant strains of downy mildew.
More recently metalaxyl resistance has been reported for downy mildew in grapevines of the Hunter Valley region. Growers have utilised Acrobat SC as a valuable alternative treatment to regain control of this disease. Metalaxyl remains a valuable fungicide for these growers but must be protected from over-use, especially in high pressure seasons.
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