The Yew (Taxus species) is a widely planted evergreen shrub prized for its dense, dark green foliage and tolerance for heavy pruning. These hardy plants provide year-round structure and color in landscapes. When the needles begin to turn brown, it signals a serious underlying problem. Diagnosing the cause of browning involves first looking closely at environmental conditions before concluding that pests or disease are to blame.
Non-Biological Causes of Browning
Environmental and cultural factors, particularly water management and winter stress, are the most frequent culprits behind Yew browning. Waterlogged soil is a significant issue because Yew roots are highly sensitive to poor drainage, which deprives them of oxygen. Prolonged saturation causes the roots to suffocate, mimicking drought symptoms by preventing the plant from taking up water and nutrients. This ultimately leads to brown, dry-looking foliage.
The opposite problem, desiccation, is a common winter injury known as “winter burn.” Yews are evergreen, meaning their needles continue to lose moisture through transpiration even when the ground is frozen. Since the roots cannot absorb water from the frozen soil to replace what is lost, the foliage dries out and the needles turn brown. This damage often appears on the side of the shrub facing prevailing winter winds or sun, and is most noticeable in late winter or early spring.
Chemical exposure also causes browning, particularly near roads or driveways treated with de-icing agents. Road salt, such as sodium chloride or magnesium chloride, damages the shrub in two ways: salt spray deposited onto the foliage and salt absorbed by the roots from the soil. The resulting browning often appears similar to winter burn, with damage concentrated nearest the source. Herbicide drift from nearby applications can also cause injury, typically resulting in discolored or deformed new growth before the affected needles brown and die.
Pests and Pathogens Affecting Yews
When environmental factors are ruled out, browning is often traced to a biotic cause, such as a fungal disease or an insect infestation. Root rot, primarily caused by the Phytophthora water mold, is the most common destructive pathogen affecting Yews. This infection is directly linked to excessive soil moisture, where the fungus thrives and attacks the fine feeder roots, causing the plant’s water-delivery system to fail. The visible symptom above ground is a gradual browning and decline of the canopy, often starting from the interior or lower branches.
Insects that feed on the Yew’s sap can also cause foliage to yellow and then brown due to nutrient depletion. Scale insects appear as small, stationary, dome-shaped bumps on the stems and undersides of the needles, protected by a waxy or hard shell. These insects pierce the plant tissue to suck out sap, which causes the foliage to become mottled and eventually turn brown. They also excrete honeydew, a sticky substance that can lead to the growth of sooty mold on the foliage.
Spider mites, tiny arachnids that thrive in hot, dry conditions, cause a different type of damage. They puncture individual plant cells to feed, resulting in tiny pale or yellow spots on the needles, known as stippling. As the infestation grows, the needles take on a grayish or bronze hue before turning completely brown. A fine, silken webbing may also be visible between the needles or branch tips.
Strategies for Recovery and Future Health
Addressing the cause of browning requires immediate, targeted action based on the identified stressor. For shrubs suffering from non-biological stress, the first step is to prune out all dead, brown wood, cutting back to the green, pliable wood to encourage new growth. Yews can tolerate severe pruning into old wood and still generate new shoots, making recovery possible even after significant damage. For water stress, improving soil drainage is paramount, often by incorporating organic matter or planting on a slight mound to allow excess water to drain away.
Preventative measures are the best defense against recurrence, especially for environmental injuries. To combat winter desiccation, deep-water the Yew late in the fall before the ground freezes. Consider erecting burlap barriers on the sunniest or windiest side of the shrub, or applying an anti-desiccant spray to the needles to reduce moisture loss. To avoid chemical injury, shield Yews from road salt spray with temporary barriers or switch to salt-free de-icing alternatives.
For biotic issues, treatment must be precise. For root rot, improving drainage is the primary long-term solution, as fungicides are often ineffective once the disease is established. Insect pests like scale and mites can be managed with targeted applications. Horticultural oils or insecticidal soaps, applied according to label instructions, are effective against both pests by smothering them. Consistent monitoring and early intervention ensure the Yew remains healthy.