The American Pillar Arborvitae has become a popular choice for residential landscapes due to its narrow, columnar growth habit. This cultivar is prized for its ability to reach impressive heights of 20 to 30 feet while maintaining a width of only three to four feet. This characteristic makes it an ideal, fast-growing solution for creating dense, year-round privacy screens and hedges. Although generally robust and low-maintenance, the American Pillar is susceptible to specific biological and environmental pressures that can compromise its vibrant green foliage. Understanding the signs of these common issues is necessary for preserving the health and aesthetic value of this distinctive evergreen.
Insect Pests and Targeted Treatments
The most common arthropod threat to the American Pillar Arborvitae is the spruce spider mite. Infestation is often difficult to spot until the foliage begins to show a dull, stippled, or bronzed appearance, particularly on the inner needles. Closer inspection may reveal fine silk webbing, a sign of a heavy mite population feeding on the needles. Treating these pests often involves applying a dormant oil spray in late winter or early spring to smother overwintering eggs. During the growing season, a targeted miticide or horticultural oil can be used, or a strong jet of water can physically knock mites off the plant.
Bagworms present another serious and visible problem, as the larvae construct spindle-shaped protective cases from silk and bits of foliage. These bags, which can grow to about two inches long, are often mistaken for small pine cones until they are noticed in large numbers. The caterpillars emerge from overwintering eggs inside the bags around late May or early June, immediately beginning to feed on the foliage and causing significant defoliation. Small infestations can be controlled by manually picking the bags off the plant and destroying them before the eggs hatch. For larger infestations, an insecticide containing Bacillus thuringiensis (Bt) or spinosad should be applied when the larvae are small and actively feeding, usually from late spring to early summer.
Fungal Diseases and Management Strategies
Fungal pathogens are responsible for several diseases that cause dieback in arborvitae, most notably tip blights. These blights typically infect new growth, causing the tips of the branches to turn tan or brown, often with small, black, pimple-like fungal fruiting structures visible on the dead tissue. The infection often starts lower in the canopy and works its way outward, resulting in scattered pockets of dead foliage. Management begins with sanitation, requiring pruning out all infected branch tips and disposing of them to reduce the fungal spores available to reinfect the plant. Pruning should be done when the foliage is dry to prevent the spread of spores, and tools should be disinfected between cuts.
Root rot is a significant fungal issue generally caused by oversaturated soil conditions, allowing fungi to thrive. Symptoms manifest above ground as a general decline, yellowing, or browning of the foliage, often starting from the bottom of the plant. Since root rot is a consequence of environmental conditions, chemical fungicides are generally ineffective as a sole treatment. The primary strategy is to immediately improve soil drainage by reducing watering frequency and, if necessary, amending the soil to prevent water from pooling around the roots.
Cultural and Environmental Stressors
Non-biological factors are frequently mistaken for pest or disease problems and can cause widespread browning. Winter burn, or desiccation, occurs when the plant’s foliage loses moisture to dry winter winds and sun faster than the frozen root system can replenish it. This damage typically appears as reddish-brown or scorched tips on the exposed side of the plant in late winter or early spring. Improper watering is another common stressor, as arborvitae are sensitive to both drought and overly wet soil. Drought stress causes foliage to turn brown and dry out, usually starting from the inner part of the plant.
Corrective Actions
Corrective actions for environmental stress involve adjusting site conditions and care practices.
- To mitigate winter burn, apply an anti-desiccant spray in late fall to reduce moisture loss.
- Establish a temporary burlap screen on the windward side for physical protection against winter winds.
- During periods of drought, use deep, infrequent watering to fully saturate the root zone.
- Protect new plantings from road salt runoff, which can severely damage foliage and roots.
Proactive Health and Maintenance Planning
When planting, the American Pillar Arborvitae should be spaced three to four feet apart to ensure adequate air circulation and discourage fungal growth. The top of the root ball should be level with the surrounding soil to prevent stem rot. Applying a two to three-inch layer of organic mulch around the base helps regulate soil temperature and moisture, but the mulch should be kept several inches away from the trunk flare. Consistent, deep watering is important for young trees during their first year and during dry spells. Providing a thorough soaking of the ground before the first hard freeze boosts the plant’s ability to survive winter desiccation.