Holly (Ilex spp.) Is a large genus of evergreen and deciduous trees and shrubs which — depending on the species — grows at U.S. Department of Agriculture plant hardiness zones 5 through 11. After the foliage of the holly bush begins to discolor, wilt or fall prematurely, you know something isn’t right with the plant. Unfortunately, various diseases attack holly bushes, resulting in damaged foliage. Identifying the offender is the first step in controlling the leaf infection. Once identified, treat according and implement preventive steps to protect the holly bush from future diseases.
Cylindrocladium Leaf Spot
Cylindrocladium leaf place presents itself as small, circular yellow discolorations on the holly bush foliage. Because the stains mature, they begin to darken to hues of tan or brown edged in blackish purple. Infected foliage falls from the holly and branch dieback happens. Controlling this respiratory disease starts with removing the infected branches with pruning shears and fixing the bush using 2 applications, 14 days apart, of thiophanate-methyl fungicide. This fungicide will also help stop the disease if implemented continuously throughout its growing stage starting at bud break with 14-day periods.
Anthracnose strikes American holly (Ilex opaca), Chinese holly (Ilex cornuta), English holly (Ilex aquifolium), winterberry (Ilex verticillata) and inkberry (Ilex glabra), causing brownish blotches to look on the foliage. Pinkish-orange spore masses will develop within the blotches, and dieback may occur. Fungicides containing chlorothalonil or thiophanate-methyl implemented in late spring can protect against anthracnose from damaging the holly bush. There is absolutely no effective chemical control once the holly bush becomes infected with this fungal disease. If the bush develops this fungal pathogen, prune diseased branches off the holly to help stop it from spreading.
Internet blight is prevalent in humid, warm weather conditions and typically affects holly shrubs with dense canopies and poor air flow. Holly bushes infected with web blight develop brownish spots in the bottom and edge of the foliage. Because the stains mature, they develop larger and darken to a black shade. These spots may cover whole leaf surfaces and will either fall from the bush or cling to the stem. Fungicides containing thiophanate-methyl, iprodione and chlorothalonil help prevent web blight but won’t cure the fungal infection. Along with preventive fungicides, make certain holly bushes are spaced far enough apart to permit air flow between the plants and through their foliage.
Botryosphaeria canker can affect most species of holly and generally appears after extreme fluctuation in temperature or after periods of drought. The leaves of infected plants begin to yellow and fall from the bush. Stems begin to girdle and dieback happens. Cankers develop on the rectum and can enlarge, girdling that limb. If not treated, the whole holly bush can succumb to the disease. No chemical treatment will control botryosphaeria canker, and emphasis is on appropriate maintenance techniques. Only develop the holly bush in well-drained soil and add mulch around the plant. The mulch protects the holly’s roots from abrupt temperature fluctuations.