With their bright red berries and glossy green leaves, holly bushes are a popular landscape plant in the United States. They are a favorite of gardeners, as well as birds and other wild animals. Holly bushes have relatively few life-threatening diseases. If you discover a disease on your holly plant, however, catching it early could save it.
Holly bushes can contract both black root root and Phytophthora root rot from water-born fungus in the soil. These fungi attack the roots, causing reduced plant vigor, yellowing of the leaves, early leaf drop and eventually the wilting of entire limbs. Once infected the hollies cannot be saved, so prevention is the top defense against this disease. Plant the bush in well-drained soil, giving it enough space to breathe. Water and fertilize properly; well-maintained plants can fight off infection more easily. Fungicides can prevent this disease. If you have an infected holly, remove it from the soil to stop spread of the fungus to other plants.
Anthracnose usually infests English, Chinese, American, inkberry and winterberry hollies. This disease manifests itself with tan or darker brown spots on the the leaves. During humid weather, you can even see pink-orange fungus spores in these spots. Severely affected plants may have twig dieback. To control anthracnose, prune out infected branches and start applying a fungicide with Chlorothalonil as the main ingredient in late spring. Reapply the fungicide every seven to 14 days.
Tar spot occurs when the airborne fungus Phacidium curtisii attacks the plant. American and English holly bushes are the most likely victims. With this disease, yellow spots appear on the leaves in May. These spots turn reddish-brown and then black by the fall. Sometimes the spots even occur on berries. To control this disease, prune out infected branches as well as other branches in the bush to increase air circulation.
Botryosphaeria canker, also called bot canker, can occur on all types of holly. This disease appears as slightly shrunken, discolored and cracked bark on twigs of the bush. The cankers spread, eventually cutting off all the nutrients to any part of the plant above the canker. This is a stress-related disease, easily prevented if you take care of the bush properly. For infected plants, prune wilting branches back to healthy, green wood and give the holly proper care.
Female nematodes build their webs and lay their eggs in the root system of holly bushes. As the young nematodes hatch, they suck on the roots and draw nutrients out of the plant. The result is a slow decline characterized by reduced vigor, yellowing or bronzing of the leaves, stem dieback, failure to respond to water or fertilizer ,and eventual death. Remove infected plants and the surrounding soil to stop the spread of this disease. There are no chemicals to treat nematodes effectively.