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Plant NameTypeDescription 
Failure to bloomHydrangeaDiseaseImproper pruning is the most common reason hydrangeas fail to bloom. Both bigleaf (Hydrangea macrophylla) and oakleaf (H. quercifolia) hydrangeas produce their flowers on the previous year's growth. If these stems are removed, new growth may fail to produce flowers that season. Panicle (H. paniculata) and smooth (H. arborescens) hydrangeas flower on current-season growth, so heavy summer pruning of these species can reduce flowering. Bigleaf hydrangeas may also fail to bloom due to environmental conditions. Freezing temperatures early in the fall before the plant is completely dormant, late-season spring frosts, and very cold winter temperatures can damage or kill developing flower buds. Plants which are placed in very shady locations may not bloom as profusely as those that receive more light.
Fungal leaf spotsHydrangeaDiseaseSeveral fungal diseases cause spotting of leaves on hydrangeas. Symptoms may include brown, black, or gray spots or angular blotches. These may be surrounded by a reddish or purple halo. Spotting may range from mild to severe and severely affected leaves may turn yellow and drop from the plant. Leaf spot diseases are usually noticed in midsummer to early fall. Cercospora leaf spot typically causes small necrotic spots beginning on the lower leaves and progressing upward on the plant. Anthracnose may cause large, round or angular blotches which can appear all over the plant, including the flower heads. Both of these diseases can be spread by splashing water and diseased plant materials including fallen leaves.
Hail damageHydrangeaDiseaseDamage to plants depends on size of the hailstones and intensity of the storm. Minor damage may not show immediately, but may appear days or weeks later as small whitish scars or spots on the leaves. More severe damage may show immediately after the storm as tears or irregular holes, or shredded leaves and flower clusters. Leaves may be torn completely off the plants. Unlike leaf spots caused by disease or insect damage, hail scars do not continue to enlarge or spread once the initial damage is done.
Herbicide damageHydrangeaDiseaseSymptoms of herbicide damage may be confused with damage from insects, disease, or cultural problems. Specific injury symptoms vary depending on degree of exposure, product used, and plant species. Damage may not appear immediately, and plants may exhibit symptoms for more than one growing season. In addition to uptake by roots and leaves, herbicides may also cause damage when they contact thin or green bark, even if they are not applied directly to the plant. Some common symptoms of herbicide injury include upward or downward cupping of leaves, as well as elongation, stunting, twisting, narrowing or distortion of leaves and shoots. Leaves may turn yellow, either between the veins, along the veins, or along the leaf margins. Products containing glyphosate may cause chlorosis, stunting, distortion, and death beginning with the youngest tissues. Again, however, the symptoms vary greatly depending on the amount of exposure. Soil-applied herbicides such as dichlobenil (Casoron) or long-term residual products may cause symptoms of inhibited root growth such as yellowing of leaves or leaf veins, leaf tip necrosis, and marginal leaf necrosis. For more information on specific herbicides, see the Herbicide Damage section of this website. Tips on pesticide use and preventing plant damage can be found at the "More information on using pesticides" link below.
Leaf scorchHydrangeaDiseaseLeaf scorch on hydrangea is a common physiological problem. Typical symptoms include yellowing leaves, or irregular dry, brown blotches. Leaf tips and margins may turn brown, as well. Severely damaged leaves may drop from the plant. Leaf scorch results when the leaves lose water faster than it can be supplied by the roots, so wilting may occur before scorch is noticed. Common causes include inadequate watering, exposure to strong light (sunlight or reflected light), high temperatures, or dry, windy conditions. Scorch can also occur as a result of damaged roots or stems, such as from an injury, compacted soils, or overwatering or overfertilization. Leaf scorch is most common on leaves farthest from the roots and those most exposed to harsh conditions--often the top of the plant and the sunniest side are most affected. Occasional minor damage is primarily an aesthetic concern, but severe or recurring damage may indicate an underlying problem with the plant's health or planting location.
Marginal leaf necrosisHydrangeaDiseaseBrowning and dieback of leaf margins and tips can be a symptom of several problems that restrict water flow to the leaves. Drought, excess heat, excess sunlight, overfertilization, and herbicide injury are all possible causes. Damage to the root system or stems may also show as wilting and leaf necrosis due to the inhibition of water uptake and movement. Salt damage may occur on plants growing near sidewalks due to winter use of de-icing products.
Powdery mildewHydrangeaDiseasePowdery mildew is a fungal disease affecting leaves, young shoots, and flowers. White to grayish, powdery fungal growth develops on the top of the leaf and may also appear on tender shoots, buds, and flowers. Leaves may also develop yellowish blotches or turn purplish-brown, with a white powdery growth on the underside. Affected plant parts may be stunted and deformed. Severely infected leaves often drop from the plant, and shoots may die back. Unlike other fungal diseases, powdery mildew does not require moist leaf surfaces for infection and is typically most prevalent during dry weather with warm days and cool nights. It thrives in conditions of high humidity, such as on plants in heavily shaded areas. While powdery mildew may occur on other species of hydrangea, bigleaf or florist's hydrangea (Hydrangea macrophylla) is most commonly affected.