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Following infection, pale-green to yellow spots, up to 5 mm diameter, develop on the upper surface. The centres of these spots become brown and necrotic with ageing. On the corresponding lower surface, raised, buff or pinkish, waxy pustules (telia) are found. As the spots on the upper surface become sunken, so these pustules become quite prominent and turn whitish when basidiospores are produced. Telia are occasionally found on the upper leaf surface. Severely attacked leaves wilt, hang down the stem and gradually dry up completely.
On Bracts and Stems
Sori sometimes develop when crops are excessively affected.
Infection has been recorded as necrotic flecking with occasional pustules (Dickens, 1970).
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
P. horiana is now a feared and serious disease in nurseries, frequently causing complete loss of glasshouse chrysanthemum crops.