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Leaf spots on primulas are yellow spots, often with dead, brown centres, and are caused by several different fungi.
Leaf spots on primulas are caused by several fungi including Ramularia interstitialis, R. primulae, Phyllosticta primulicola and Puccinia primulae, and appear during wet weather from spring until winter, persisting on leaves all year.
Leaf spots can occur on primulas, polyanthus and auriculas, although are less common on auriculas.
You may see the following symptoms:
The fungicides tebuconazole (Bayer Fungus Fighter Concentrate), tebuconazole with trifloxystrobin (Bayer Fungus Fighter Plus), and triticonazole (Scotts Fungus Clear Ultra and Scotts Fungus Clear Ultra Gun) are approved for the control of rust diseases on ornamental plants. They would probably also give useful control of primula leaf spot fungi (and the term 'leaf spot of ornamentals' is included on the label for Bayer Fungus Fighter Plus) .
The following products contain a combination of both insecticide and fungicide, enabling the control of both insect pests and disease: myclobutanil containing cypermethrin (Bayer MultiRose 2, Doff Rose Shield, Vitax Rosegarde, Westland Rose Rescue); tebuconazole containing deltamethrin (Bayer Multirose Concentrate 2), and triticonazole containing acetamiprid (Scotts Roseclear Ultra and Scotts Roseclear Ultra Gun). When a proprietary product contains an insecticide as well as a fungicide it would be preferable to use an alternative product if pests are not a problem on the plants treated.
Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)
Chemicals: using a sprayerChemicals: using safely and effectivelyChemicals: storing and disposing safely
Species of Ramularia and Phyllosticta cause leaf spots on many plants. Ramularia infections are sometimes called white moulds because of the white fungal outgrowth from infected tissues. Infections caused by rust fungi in the genus Puccinia are not strictly classified as leaf spots, but the symptoms caused by P. primulae on primulas will be seen by gardeners as spots.
Ramularia and Phyllosticta produce spores in the infected tissue and these spread by water to form new infections. They can also survive over winter in dead tissues in the form of resting structures. Since most primulas are perennial, there is probably some survival of the pathogens in lesions on leaf rosettes from one year to the next.
Puccinia primulae spreads by means of airborne spores produced from the small orange structures on the undersides of infected leaves. It also has a type of resting spore which carries the fungus through the winter, although it can also survive as infections on the leaves of perennial rosettes. The whole life cycle is completed on primulas, there is no alternate host. Puccinia primulae seems to be confined to Primula vulgaris (primrose) and P. veris (cowslip).
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