Apple scab is caused by the fungus Venturia inaequalis. This disfigures fruit and causes leaf loss, which reduces trees' vigour. It is usually treated with regular applications of conventional fungicides, but these face increasing use restrictions at EU level and are losing effectiveness as the fungus develops resistance.
Continental trials of a strain of the parasitic fungus Cladosporium cladosporioides H39 could potentially provide an alternative. Wageningen University & Research representative Nora de Rijk said: "H39 seems to be very successful in reducing scab on fruit and leaves, delivering the same results as conventional fungicides."
The trials are by several research bodies in eight orchards across the Netherlands, Germany, Poland and Hungary containing a range of varieties. They include both preventive and curative spraying in conventional and organic growing systems.
A paper documenting the findings in the US journal Plant Disease concludes: "Better understanding of the biology of the antagonist will help to further exploit its use in apple scab control."
Meanwhile, a biological control supplier is currently looking at making the fungus commercially available, de Rijk added.