Tomato leaf mould, caused by Passalora fulva, is a destructive foliar disease of increasing importance. Outbreaks have occurred most years over the past decade, affecting a range of varieties. Previously well controlled by genetic resistance, new outbreaks appear to be caused by the cultivation of varieties with no claimed resistance and the emergence of strains capable of overcoming the resistance genes deployed in current varieties.
This project aimed to provide tools for improved management of tomato leaf mould in both conventional and organic crops through identification of effective conventional fungicide and biofungicide treatments.
In the experimental system used, reliable development of tomato leaf mould required high levels of inoculum and prolonged periods of high humidity. Any glasshouse management strategies that reduce relative humidity could therefore be expected to contribute effectively to leaf mould management.
Four fungicides and four biofungicides, two of which are not yet approved, were tested against a water control to evaluate their efficacy. Each product was sprayed only once but at different timings, ranging from five days before to five days after inoculation. This was to establish any curative action of products against P. fulva or to determine whether they only acted preventively.
While all treatments reduced incidence of leaf mould compared with the untreated two weeks after inoculation, Amistar-treated plots contained fewest infected plants. Of the other conventional fungicides assessed, Switch, Signum and Teldor were also shown to be effective, with treatment timing showing that all were most effective when applied as protectants. The biological fungicide Serenade ASO also had good efficacy when used preventively and under low disease pressure.