University of Maryland Extension

Viruses - Trees

Mottled leaf pattern caused by a virus

Virus symptoms often include color changes in the leaves such as a mosaic or mottled pattern of light and dark green. Other color changes could appear as ring patterns of light green or necrotic areas. Additional symptoms include stunted or malformed new growth, unusual flower colors, and dieback of terminal growth. These disease symptoms in many plants can be confused with nutritional deficiencies or environmental effects such as air pollution.

Most plant viruses cause systemic infections and there is no cure for infected plants. Plant viruses are commonly spread from plant to plant by insects that feed on sap such as aphids, thrips, and whiteflies. Other common modes of virus dissemination include infected seeds, sap, divisions, grafted plant varieties, bulbs, and pollen. Viruses can also be spread by horticultural activities such as vegetative propagation and pruning. Many viruses can survive in weeds adjacent to the horticultural plants that become infected in our gardens.


The management of virus diseases often involves removal of the infected plant to prevent spread to adjacent healthy plants. Insect management is critical since viruses can also move through the garden in insects feeding on infected plants before feeding on nearby healthy plants. Weed removal is also very important since they can be the primary source of infected plants where insects breed or overwinter before moving onto healthy plants in the garden. Never knowingly plant virus infected varieties into your garden. Purchase certified virus clean stock and be alert to remove plants that exhibit disease symptoms.

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