Viburnum is a group of plants that comprising 150 ornamental species. These are commonly used in residential and commercial landscapes throughout the United States for the showy berries and flowers they offer. They have a medium to fast growth rate and are easily maintained. In some cases, this plant can be damaged by insects or disease, which causes the leaves of the plant to curl.
Aphids most commonly damage the leaves of the snowball viburnum. Snowball aphids (Neoceruraphis viburnicola) can be seen on the leaves of the tree and appear to be grey or dark green. These aphids feed on the tissue and sap, causing the branches and leaves to twist and curl. In most cases, aphids can be prevented and treated with insecticidal soaps available at garden centres. This product should be applied per manufacturer instructions to coat the entire plant. For optimal results, repeat this process three times, with five to seven days between applications.
Flower thrips (Frankliniella tritici) are small winged insects that measure 1/16 inch in length. It can be found on the leaves and flower petals. Adults and nymphs live on the plant and feed on its sap. As they feed, the leaves become discoloured and often appear to have purple or red shots. In severe cases, damaged portions have leaves that curl or roll and, eventually, fall from the plant. Another symptom of flower thrips is that buds will not open and leaves will appear streaked. Insecticidal sprays are effective in controlling thrips. They should be applied three times, five to seven days apart.
Downy mildew (Plasmopara viburni) is a disease that infects many ornamental plants. This mildew is caused by a fungus and rapidly spreads during wet, warm spring and summer months. As this disease infects the plant, it causes the leaves to turn red, then brown. As the leaves become damaged, they shrivel and curl before completely falling from the branches. The best way to prevent the disease is to keep the plant and soil from becoming overly wet. When symptoms are present, apply fungicides.
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