St. Paul, Minn. (December 5, 2006)—Long ago, holly was thought to have magical powers because its leaves kept their green color even during the severest of winters. Boughs of holly were hung in homes to keep bad spirits at bay and good spirits nearby. Today, the real magic of holly stems from its ability to bring beauty to homes every holiday season, say plant pathologists at the American Phytopathological Society (APS).
According to Mike Benson, professor of plant pathology at North Carolina State University, American and English hollies, with their dark-green glossy foliage and bright red berries, are the hollies most commonly used for greenery in homes during the holiday season. Plant pathologists, or plant doctors, work with nurseries that grow hollies to keep the plants healthy and in ample supply by managing the plant diseases that affect holly.
"Plant diseases such as web blight, black root rot, and root-infecting nematodes can prove challenging for nurseries and some of these disease problems can occur on hollies once they are planted,” Benson said. Plant parasitic nematodes, which are microscopic roundworms, live in the soil and attack holly roots. As the nematodes feed on plant roots, the diseased roots can no longer provide nutrients and water like healthy roots can. Above ground, the lack of nutrients and water create symptoms such as yellowing, dwarfing of leaves, and poor growth.
“Members of APS through their university and government research programs have identified specific holly cultivars that are resistant to nematode attack,” said Benson. “These resistant cultivars can be grown in the landscape where nematodes have been a problem in the past,” he said.
Black root rot, a fungal disease caused by a soilborne pathogen, affects hollies in much the same way as nematodes. The name of the disease comes from the black color of the spores produced by this pathogen in infected roots. Plant pathologists have devised several methods of prevention for black root rot including lowering the soil pH, selecting disease resistant holly cultivars, and drenches of fungicides to prevent the disease in nursery plants.
Another disease that impacts holly health in the landscape, especially Japanese holly, is dieback, said Austin Hagan, extension plant pathologist at Auburn University. This disease usually occurs during hot and dry weather conditions. “Dieback is caused by a fungus that gets into the plant and girdles the branches. This causes the branches to slowly die back to just above the soil line,” Hagan said. The best way to manage this disease is to prune out the dead or dying branches. “If managed correctly, a holly plant that gets dieback one year usually won’t have it the following season,” he said.
The American Phytopathological Society (APS) is a nonprofit, professional scientific organization. The research of the organization’s 5,000 worldwide members advances the understanding of the science of plant pathology and its application to plant health.