Black Leaves on a Holly Bush
Holly plants are frequently infested with a fungal infection called sooty mold that blackens leaves. The mold is usually more of a cosmetic problem than a serious illness on most plants, but it can cause serious problems in holly plantings. Does this Spark an idea?
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Features
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Insects such as scale, aphids, mealybugs and whiteflies have piercing mouthparts that they use to attach themselves to holly foliage and suck out plant juices. They excrete large amounts of a watery, sticky-sweet substance called honeydew that falls on leaves, stems and fruit. The honeydew acts as a growing surface for the sooty mold fungus.
Effects
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Plants infested with sooty mold develop strands of fungal tissue that cover the foliage with a thick layer of charcoal black fungus. The disease blocks out sunlight and interferes with the plant's ability to conduct photosynthesis. Seriously infested plants may have reduced vigor, which leaves them susceptible to diseases and environmental stress. Holly that grows under shady conditions is at risk of serious damage or death because its leaf chlorophyll cannot function under the layer of mildew.
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Prevention/Solution
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Sooty mold does not enter the holly's leaf tissue and can be washed off, but the fungus will reappear unless the insects are eradicated. Cornell University recommends spraying plants with an appropriate insecticide at the first sign of honeydew-producing insects. Products such as horticultural oils and insecticidal soaps, which can be purchased at most nurseries, will kill insects while loosening and removing the mold from the plant's surface.
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