Holly bushes belong to the Ilex plant family, which has nearly 400 different varieties. The shrubs have prickly edged, dark-green, shiny foliage and red berries. The fruit is not edible by humans but is a favorite with small mammals and birds. Holly bushes range in size from 1 to 70 feet and grow in full sun and well-drained, acidic soils. The majority of problems with holly bushes are due to fungi. Holly shrubs are also susceptible to temperature fluctuations and iron deficiency.
Holly Leaf Spots
Holly bushes are susceptible to leaf spots commonly caused by the Phacidium curtisii and Coniothyrium ilicinum fungi. Holly leaf spots are also referred to as holly tar spot. The disease is characterized by the appearance of irregular, yellowish brown spots on the foliage in winter and spring. In cases of heavy infection, there is premature leaf drop. The leaf spot changes to a red-brown during summer. The disease is not significantly damaging to plant health and can be controlled by making sure plants are healthy. Pay particular attention to watering, mulching and fertilization routines.
Botryosphaeria canker, or bot canker, is a common fungal problem with holly bushes. The disease is caused by Botryosphaeria dothidea, a fungus that frequently invades woody ornamentals. The fungus is an opportunistic pathogen that destroys sapwood tissues and bark and creates lesions or cankers. These cankers enlarge and gradually girdle and kill branches and limbs. As the cankers move to the main stem, they can kill the plant. The fungus usually infects the plant through pruning cuts and cracks, and symptoms can take up to 3 months to a year to fully appear. Best preventive measure is to make sure plants are healthy. Fungicidal controls are not effective and usually not recommended.
Holly scorch or leaf scorch is a common noninfectious disease of holly shrubs and a number of other shrubs and trees. Holly scorch occurs frequently after windy, dry weather and in stressed plants including those planted in infertile and dry soil. Mild infection does not cause major damage, but defoliation and withering of leaves occurs when disease progresses. The disease is characterized with bronze or yellowing leaves due to inadequate supply of water through the plant. Holly scorch is mainly an environmentally caused problem and can be prevented by improving the general health of the plant.