Holly is a genus comprising 600 flowering plant species. It is part of the Aquifoliaceae family and includes both shrubs and trees. The plant bears moderately sized red berries shaped like globes. The berries are relatively toxic and can cause stomach upset if ingested. The plant is particularly popular during the holiday season, when it is used to make Christmas wreaths. Although hollies are very hardy, as with any plants, there are some possible diseases that could affect them.
Various different leaf spots affect hollies, the most serious of which is called tar spot. It is a fungal disease that can appear at any point in the growing season but is much more common in the beginning of the spring when it is cool and moist. The initial symptom of tar spot is the development of yellow spots, which later become deep brown. By the autumn, the spots turn almost black. The leaves that are diseased should be collected and destroyed. Fungicides such as a copper fungicide or maneb can be applied.
Cankers are another possible disease that can be troublesome to holly plants and is characterized by sunken areas on the stems. These gradually die out. It is important to prune any of the branches that are infected by the cankers in order to salvage the plant. Cankers can also be prevented by improvement of air circulation, and also by making sure debris is picked up and removed from the area of the healthy plant.
Holly plants also experience several environmental diseases, which can occur because of injury to the plant, deficiencies of nutrients and drought. Some examples include spine spot (grayish-purple spots), purple blotch (purple spots appearing on the leaves), chlorosis (yellow or light green leaves with deep green veins) and holly scorch (the leaves turning brown).