Answer: Very few diseases occur on Shasta daisies so I wonder if the plant is suffering from a condition called Oedema? Oedema occurs when roots take up water faster than it can be used by the plant or transpired through the leaves. Water pressure then builds up in the mesophyll or internal cells of the leaf causing them to enlarge and form tiny swollen blister?like areas.
Oedema appears as small, sometimes corky blisters which form on the lower surface of leaves or needles. These blisters may eventually harden to form white, tan, or brown wart?like corky bumps on the lower leaf surface. In severely affected plants these corky growths also form on petals, petioles, and stems. As injury continues, leaves turn yellow, droop, and fall off. Plants become spindly and growth ceases.
Overwatering, high humidity, and low light intensities are factors which favor the development of oedema. Avoid overwatering susceptible plants especially during the winter months when they should be kept slightly on the dry side. Keep the relative humidity below 70% in the winter. Improve the flow of air over the leaves by spacing plants farther apart and increasing ventilation. Affected plants often recover from oedema with the return of more favorable growing conditions in spring and early summer. Or, you can replace the plants with healthy new specimens.
If these descriptions do not match the symptoms on the plant, you might want to have the customer take the plant to the local cooperative extension office for diagnosis.
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