For those with a more-is-better gardening philosophy, the Endless Summer hydrangea (Hydrangea macrophylla “Bailmer” Endless Summer) is a perfect match. The first hydrangea to bloom on old and new growth, Endless Summer flowers through mid- and late summer across U.S. Department of Agriculture plant hardiness zones 5 through 9. Its bold, spherical blue or pink flowerheads continue long after other hydrangeas have faded. Only a handful of diseases -- none serious -- trouble the 3- to 4-foot shrub.
Planting your Endless Summer hydrangea in too much shade exposes it to powdery mildew fungal infection. Wind carries the fungal spores to the shrubs' leaves, where they germinate into mats of white, powdery fungal strands. The disease may distort new growth or cause older leaves to fall prematurely. Powdery mildew is unusual because it spreads only on dry tissues. Situating your hydrangea in a sunny location and sprinkling the foliage when you water it reduce its risk of infection. Pruning and disposing of infested foliage and clearing away spore-harboring fallen leaves also discourage the disease.
Botrytis blight (Botrytis cinerea) or gray mold fungus targets an Endless Summer shrub's old or wounded parts during cool, damp weather. In Mediterranean climates, it's most active during the fall and winter rainy seasons. Blight surfaces as small saturated spots on the flowers before expanding into reddish-brown patches. Wilting, decayed flowers sprout fuzzy grayish or brownish spores. Infected petals dropping onto healthy wet buds and leaves spread the disease. Blighted buds often die without opening. Remove aged or damaged flowers and leaves along with debris, and prune and destroy diseased plant parts at the first sign of infection to eliminate them as spore sources. Other preventive measures include thinning the canopy for improved air circulation and keeping the shrub dry when you water.
Warm, wet weather exposes Endless Summer hydrangea to bacterial leaf spot (Xanthomonas campestris) infection. Bacteria splashed onto the leaves penetrate wounds or stomata, the plant’s breathing pores. Small, angular water-soaked leaf spots deepening to brown or purple as they expand indicate infection. Typically progressing upward from the lower branches, they frequently destroy enough tissues to kill infected leaves. To prevent leaf spot’s spread, avoid splashing the plant whey you water it. Wait for a dry day to prune diseased leaves and clean up the fallen ones.
If an Endless Summer shrub starts wilting in the heat of the day and recovers after sundown, suspect bacterial wilt (Ralstonia solanacearum, Pseudomonas solanacearum). The disease strikes damaged roots in excessively wet soils. Unless the soil dries, the entire shrub wilts and eventually dies, although its withering leaves remain green. Peeling back the bark of the lower stems exposes discolored, brown vascular tissue. Planting your hydrangea in well-drained soil and watering only to maintain its vigor offer some protection. Because no bacterial-wilt treatment exists, removing an infected shrub is likely the only way to save your other plants.
- Missouri Botanical Garden: Hydrangea Macrophylla “Bailmer” Endless Summer
- University of California Statewide Integrated Pest Management Program: Powdery Mildew
- Pacific Northwest Plant Disease Handbook: Hydrangea -- Bud and Flower Blight
- University of California Statewide Integrated Pest Management Program: Gray Mold
- Michigan State University Extension: Bacterial Leaf Spot on Hydrangeas
- University of California Statewide Integrated Pest Management Program: Bacterial Soft Rots, Leaf Spots, Blights, Wilts
- University of Florida IFAS Extension: Disease Management -- Bacterial Wilt
- Penn State University Extension: Bacterial Wilt -- Ralstonia Solanacearum
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