The holly is native to the eastern and southern parts of the United States and thrives in USDA hardiness zone 5. It is an evergreen that grows up to 50 feet high, though it is most commonly seen at 15 to 30 feet high. The dull, dark green leaves grow up to 3 ½ feet long and have short spines. The holly produces small, white blooms in June. The male plants produce flowers in groups of three or more, and the female plants produce only solitary flowers. The red fruit grows on stalks, and only on female plants. It matures in October and stays on the plant in the winter.
There are two types of scale insects: soft scales and armored scales. The soft scale moves between branches and leaves during its lifetime. It produces honeydew, a sticky substance that coats the plant, and eventually produces black sooty mold. The armored scale has a hard cover. It stays on the branches of the holly and does not produce honeydew. Both types are so small that they are difficult to see. They suck the sap from the plants, which weakens the plant and invites other pests. You can control scales by keeping the plant healthy and introducing natural controls or by using pesticides.
Southern Red Mite
The Southern red mite (Oligonychus ilicis) is a reddish-brown pest that is less than 1/50 of an inch long. It has sucking mouthparts that it uses to feed on the bottom of the leaves of the holly plant. It produces a fine webbing. The main symptom of the Southern red mite is yellow speckling on the leaves. If the infestation is severe, the webbing is seen on the top and bottom of the leaves, instead of just the bottom. Control the Southern red mite by introducing predatory bugs, such as ladybird beetles. You can also remove them by spraying them with a strong spray of water or by applying insecticides.
Phytophthora Root Rot
Phytophthora root rot is caused by a water mold fungus, the Phytophthora cinnamomi. It affects holly that is grown in poorly drained soil or in wet areas. According to Clemson University, over-mulching also introduces the fungus that causes Phytophthora root rot. Signs include yellowing leaves, slowed growth and early leaf drop. Limbs also wilt and die back to the trunk. The root rot might leave a brown or black streak of dead tissue that extends from the damaged limb to the rotted roots. Eventually, the holly dies. To treat root rot, make sure the plant is watered properly and that the soil is well-drained. Fungicides that contain etridiazole and mefenoxam kill the fungus, but do not cure the infected plant. Remove and discard infected plants.