Diseases of Holly Bushes
With their bright red berries and glossy green leaves, holly bushes (Ilex spp.) 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 problems, although there are a few common holly tree diseases. If you discover a disease on your holly plant, however, catching it early could save it.
Holly Tree Disease Root Rot
Holly bushes can contract both black root root and Phytophthora root rot from water-born fungal pathogens 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.
The Clemson Cooperative Extension notes that hollies succumb to fungal root rots when planted on poorly draining soil or when overly mulched. Plant the bush on well-draining soil, giving it enough space to breathe. Water and fertilize properly; well-maintained plants can fight off infection more easily. A holly bush fungus treatment with a fungicide can help prevent this disease. If you have an infected holly, remove it from the soil to stop spread of the fungus to other plants.
Anthracnose Holly Fungal Disease
Anthracnose usually infests English (Ilex aquifolium, USDA zones 7-9), Chinese (I. cornuta, zones 7-9), American (I. opaca, zones 5-9, inkberry (I. glabra, zones 4-9) and winterberry (I. verticillata, zones 3-9) hollies. This disease manifests itself with tan or darker brown spots on the the leaves. During humid weather, you can even see pinkish-orange fungal 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, or according to label directions if they vary from this recommendation.
Tar Spot Holly Fungal Disease
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 Bark Disease
Another holly bush plant disease is Botryosphaeria canker, also called bot canker, which 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.
Holly tree bark diseases, such as bot canker, generally are stress-related, 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.
Nematode Damage to Hollies
Nematodes can cause symptoms that resemble those caused by disease, and their feeding on plant roots can also create openings that allow disease pathogens to enter. 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. If you do remove an infected plant, Penn State Extension recommends fumigating and aerating the soil before planting another holly on the same site.