Testing new fungicides to reduce apple scab

The reduction of mycelium growth of scab Venturia inaequalis strains on malt agar amended with pyrimethanil, a pyrimidinamine, was reduced on a lower level (ED50 0.28 - 33.8 mu g a.i./ml) compared with other side specific compounds such as Demethylation inhibitor fungicides. Good disease control was obtained in apple seedling tests with 2 strains which showed low and high sensitivity in vitro. The results are discussed in relation to the test method and the mode of action of pyrimethanil. The fungicidal activity of the new Demethylation inhibitor fungicide fluquinconazole against V. inaequalis strains (44) was compared with flusilazole and fenarimol in mycelium-growth tests. Positive cross resistance for all less sensitive strains was found. Fluquinconazole was the most active compound.