Easily identifiable by its upright, columnar growth habit, the "Sky Pencil" holly (Ilex crenata "Sky Pencil) works well as an accent plant, container specimen or a natural screen when planted in mass. This evergreen shrub grows in U.S. Department of Agriculture plant hardiness zones 5 through 9. A Japanese holly (Ilex crenata) cultivar, "Sky Pencil" proves susceptible to the same diseases that affect its parent plant.
Botryosphaeria canker, also known simply as die-back, occurs when the Botryosphaeria fungus enters the "Sky Pencil" holly's system through breaks or cuts in its stems. The fungus causes the bark and woody tissue around the infection to collapse and turn brown to black. This canker stops the movement of water and nutrients through the stem, resulting in yellow leaves that begin to drop and stem dieback. Cutting back diseased stems to at least 1 inch below the canker will stop the disease from spreading throughout the plant. Prevent infection by watering the plant when the top 1 to 2 inches of soil becomes dry and pruning out broken or damaged branches as they occur.
Rhizoctonia aerial blight, or web blight, attacks "Sky Pencil" holly when prolonged rainfall, high humidity and warm summer temperatures combine. This fungal disease spreads quickly, attacking the plant's lower leaves first then spreading upwards. Browning leaf margins develop into irregular brown to black discolorations across the leaf's surface. Dry, sunken, brown cankers form on the infected plant's stem near the soil. Plant your holly in an area with adequate air circulation, thin its stems yearly and water during the morning hours to allow the foliage to dry before nightfall to prevent web blight from forming. Spray infected specimens with a fungicide every seven to 14 days to kill the fungus.
Caused by the fungus Cylindrocladium, leaf spot appears first as irregularly shaped, yellow spots. As the disease progresses, the spots turn purplish-black and develop light-green margins. If left untreated, the leaves will die and fall off the "Sky Pencil" holly, leaving bare stems that eventually will die. Buy only healthy plants from reputable sources to avoid introducing the fungal spores into your landscape. Keep the ground around the holly clear of fallen leaves and other debris to eliminate breeding spots for the fungus. Treat leaf spot by spraying the infected foliage with a fungicide mixed at 1 tablespoon per gallon of water every 10 to 14 days.
"Sky Pencil" holly specimens require fast-draining soils that allow oxygen to reach their roots. When planted in heavy soils that retain moisture and prevent oxygen penetration, root rots such as Phytophthora, Pythium and Thielaviopsis black rot occur. These fungal diseases cause the roots to turn brown or black and become mushy. As the roots die off, the holly's foliage begins to yellow and die as well. Avoid overwatering your holly plant to the point that the soil remains soggy or develops standing water. Prevent root rot from developing by planting healthy stock in loamy soils. Water the holly when the top 1 to 2 inches of soil dries to allow oxygen to reach the roots.
- Monrovia: Sky Pencil Japanese Holly Ilex Crenata "Sky Pencil"
- The United States National Arboretum: Ilex Crenata "Sky Pencil"
- University of Arkansas: Hollies for the Home Garden
- Alabama Cooperative Extension System: Common Diseases of Holly and Their Control
- Penn State Extension: Botryosphaeria Canker
- Greenhouse Product News: Rhizoctonia Diseases on Ornamentals
- Penn State Extension: Cylindrocladium
- University of California IPM Online: Pythium Root Rot