Irish Leaf Spot

Older leaves of many ornamental plants are pone to leaf spots, but the strong sword-shaped leaves of iris look particularly disfigured when they are infected. This is largely because the spots become enlongated along the direction of the veins on the leaf. The brown oval spots appear at random, and the centre of the spot is often lighter in colour, sometimes showing the spores of the fungus. In severe cases the spots coalesce and the leaf dies. A wide spectrum fungicide, such as dithiovarbonate, should be used to control it, but make sure that there is no spray drift onto the pool surface.