Remove and dispose of all leaf debris at the end of the year.If chemical controls are used, they should be used only in a minimal and highly targeted manner. The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. Flowers may develop patches of irregular colouration (‘flower breaking’).Leaves develop light green or yellow flecks and mottles.Plants grown from affected bulbs may be stunted with leaf yellowing, and may die.White, orange or blue-green fungal growth may be visible on or within the bulb.Bulbs may rot in the ground or during storage.Eventually the whole ‘fan’ of leaves may collapse onto the groundīulb rots ( Fusarium and Penicillium species) Leaves develop a soft rot at the base, turn yellow and wither.Decay usually starts in the youngest part of the rhizome, but may spread to affect a large proportion of it.The rhizome develops a slimy, often foul-smelling rot.Rhizome rot ( Pectobacterium carotovorum) Severely affected leaves may turn a more uniform yellow and wither from the tip.As summer progresses, these orange-brown pustules are replaced by black ones.Close examination will reveal that each spot contains an orange-brown ‘pustule’ of spores.Numerous small, pale green or yellow leaf spots develop.Both rhizomatous and bulbous iris can be affected.Severely affected bulbs rot to leave an outer ‘shell’ containing a mass of black fungal spores.Ink-like black blotches may be present on the exterior of bulbs.Leaves develop black blotches and, if severely affected, turn yellow or reddish-brown and wither.Seen most commonly on the bulbous Iris reticulata and Dutch irises.A ‘sooty’ growth, consisting of large numbers of fungal spores, may develop on the surface of the spot in wet weather.Heavily infected leaves may have much of their leaf area affected, and will eventually shrivel and die.The spots are lens-shaped in the early stages but usually enlarge and merge together.Watersoaked leaf spots develop, which turn brown and may have a yellow margin.Seen most commonly on Iris germanica (bearded iris), but other rhizomatous and bulbous types can be affected.Malvern Autumn Show - 23–25 September 2022ĭepending on which disease is to blame, symptoms may vary as follows:.RHS Garden Wisley Flower Show - 6–11 September 2022.RHS Garden Rosemoor Flower Show - 19–21 August 2022.RHS Garden Hyde Hall Flower Show - 3–7 August 2022.RHS Flower Show Tatton Park - 20–24 July 2022.RHS Hampton Court Palace Garden Festival - 4–9 July 2022.RHS Garden Harlow Carr Flower Show - 23–26 June 2022.RHS Botanical Art and Photography Show - 9–29 April 2022.RHS Garden Wisley Spring and Orchid Show - 25–27 March 2022.