Causes of phyllody
Environmental: Factors such as late frost, hot weather or water stress during flower development can cause hormonal imbalances resulting in phyllody. Environmentally-induced phyllody does not usually affect all flowers.
Control: If the cause is environmental, the plant will produce normal flowers later in the growing season or during the following season. Some plants such as roses, clovers, asters and strawberries seem to be particularly susceptible. Remove the affected flowers, if desired. If practical, protect from cold damage, e.g. with fleece, and prevent drought stress.
Disease: Phyllody can be a symptom of phytoplasma infection. Phytoplamas are bacteria-like parasites that grow and multiply in the vascular tissue of plants. They are usually spread from plant to plant by plant-sucking insects such as leafhoppers and mites.
Control: Once infected with a phytoplasma, plants will always produce distorted flowers. There is no cure and plants are best destroyed. Control insect pests to prevent spread of the infection. Do not propagate from infected plants. Keep pruning and propagation tools clean.
Weedkiller damage: Weedkiller contamination can also cause abnormal growth. Accidental contamination from spray drifts, accumulation of weedkillers in compost or mulch, or over application of path/drive weedkillers close to borders.
Control: Depending on the severity of damage, affected plants often recover, but it may take time. See manure and weedkiller contamination for more information.