Arborvitae are popular evergreens, often chosen for privacy screens. However, brown spots are a common concern. Understanding, diagnosing, and addressing these issues maintains healthy plants.
Understanding Why Arborvitae Turn Brown
Arborvitae foliage browns due to environmental stressors, pests, or fungal diseases. Identifying the cause helps address the problem.
Environmental Stressors
Environmental factors cause browning. Winter burn results from cold, drying winds, and lack of water when ground is frozen. Foliage loses moisture, but roots cannot absorb it, leading to desiccation and browning, often at branch tips.
Drought stress during hot, dry spells causes leaves to yellow and crisp. Overwatering can lead to root rot, where roots suffocate and decay, mimicking drought symptoms. Other causes include salt damage, pet urine (high nitrogen), and insufficient sunlight for inner branches.
Pest Infestations
Pests damage plant tissues, causing browning. Spider mites, tiny arachnids, feed by piercing leaves and sucking plant fluids, causing discoloration. Fine webbing indicates their presence.
Arborvitae leafminers tunnel within foliage, turning branch tips brown. Bagworms, caterpillars constructing spindle-shaped bags, defoliate branches. Scale insects appear as small bumps on bark, weakening the plant.
Fungal Diseases
Fungal pathogens commonly cause brown spots. Root rot, often from overly wet soil, is a serious issue where fungi like Phytophthora infect feeder roots. This prevents water and nutrient absorption, leading to yellowing, wilting, and browning downwards.
Blights, such as Cercospora and Kabatina, also cause foliage to brown. Cercospora blight typically starts on inner, lower portions and moves upward. Phomopsis blight causes tip blight, with tiny yellow spots becoming reddish-brown shoots. These diseases thrive in damp, humid conditions.
Diagnosing the Specific Problem
Diagnosing brown spots requires observing browning pattern, timing, and other signs. First, note normal seasonal needle drop: older, inner foliage turns yellow or brown and sheds, usually in fall. This natural process reallocates resources to newer growth.
If browning is not seasonal, examine affected foliage. Browning at branch tips moving inward, especially in winter or early spring, suggests winter burn or desiccation. Browning on one side or in exposed areas also indicates winter damage. If entire branches or large sections brown during dry periods, drought stress is probable.
Conversely, yellowing leaves that fall easily, or soft, mushy bark, suggest overwatering and root rot. Inspect foliage for pests: fine webbing indicates spider mites, while small, camouflaged bags point to bagworms. Look for tiny black spores or cankers on branches, signifying fungal diseases. Root rot is confirmed by checking roots (healthy roots are white, rotting roots are yellow or brown). Timing provides clues: summer browning suggests drought or pests, while winter browning indicates environmental stress.
Effective Solutions for Brown Spots
Addressing brown spots requires tailored actions. For winter burn or drought stress, consistent, deep watering is paramount. Ensure soil remains moist but not waterlogged, especially before ground freezes in late autumn.
For pests, a strong water stream can dislodge spider mites, or horticultural oils can be applied. Bagworms should be physically removed and destroyed before larvae hatch.
For fungal diseases like blights, prune out infected portions to prevent spread. Remove brown, dead, or diseased branches, cutting back to healthy green tissue. Sanitize pruning tools. In severe cases, a fungicide may be necessary, alongside good air circulation and avoiding overhead watering.
If root rot is suspected from overwatering, improve drainage and allow soil to dry between waterings. Severely damaged plants not recovering after several seasons may need replacement.
Maintaining Healthy Arborvitae and Preventing Issues
Proactive care prevents brown spots and maintains healthy arborvitae. Proper planting is fundamental: arborvitae thrive in full sun to partial shade and well-drained soil. Ensure the root ball top is level with or slightly above ground to prevent stem rot.
Consistent watering is essential, especially for newly planted arborvitae, which need frequent moisture until established. Established plants benefit from one to two inches of water per week. A 2-3 inch layer of organic mulch around the base helps retain soil moisture, regulate temperature, and suppress weeds. Keep mulch a few inches from the trunk.
Winter protection is crucial in colder climates. Deeply water plants in late fall before ground freezes for dormant season moisture. Burlap screens shield plants from drying winter winds and sunscald. Tying up multi-stemmed arborvitae with twine prevents branches from splaying or breaking under heavy snow and ice. Regular inspection for early signs of pests or diseases allows timely intervention.