The yew (Taxus species) is a durable evergreen shrub with dense, dark-green foliage. When this resilient plant turns a dull bronze or brown, it signals a serious underlying issue. This discoloration is a common response to environmental stress or biological attack. Understanding the specific cause is the first step in restoring the yew’s health.
Environmental Stressors Leading to Browning
Browning is most frequently caused by planting environment and soil conditions, often starting at the root level. Yews are highly intolerant of overly wet soil, a condition commonly called “wet feet.” Poor drainage, especially in heavy clay, waterlogs the roots and deprives them of oxygen. This lack of aeration encourages water mold pathogens, such as Phytophthora, leading to root rot. The damaged roots cannot absorb water, resulting in the browning of the needles above ground.
Insufficient moisture also causes the foliage to desiccate and turn brittle brown. Prolonged dry periods deplete the plant’s moisture reserves, which is exacerbated by winter burn. Winter burn occurs when bright sun and strong winds draw moisture from the needles, but frozen soil prevents the roots from replacing the lost water. The resulting damage is typically visible in late winter or early spring, often appearing most severely on the south and west sides.
De-icing salts used on sidewalks and roadways are another factor. Salt runoff washes into the soil, where high concentrations of sodium ions damage the fine root tissues. This root damage restricts the plant’s ability to take up water, causing the foliage to brown, usually starting on the side closest to the salted surface.
Identifying Pests and Pathogens
If environmental factors are ruled out, browning may be caused by insects or fungal diseases. Sucking insects extract the plant’s sap, leading to discoloration and needle drop. Scale insects, such as yew scale, attach to the stems and feed on the plant’s vascular system.
Their feeding causes needles to yellow and turn brown as they excrete honeydew, a sticky substance. This sugary residue often promotes the growth of black sooty mold, a visual indicator of scale or mealybug infestation. Another common pest is the spider mite, which thrives in hot, dry conditions. Mite damage initially appears as tiny yellow or white dots (stippling), which eventually merge, giving the foliage a dull, bronze appearance before the needles are shed.
Fungal diseases, collectively known as needle blight, also contribute to browning, especially following periods of high humidity. Fungi infect the needles, causing them to turn yellow, then gray, and finally brown before they drop prematurely. Close inspection may reveal tiny, dark, fruiting bodies on the surface of the affected needles. Root-feeding pests, such as black vine weevil larvae, chew on the roots, mimicking root rot symptoms by hindering water and nutrient uptake.
Immediate Steps for Yew Recovery and Long-Term Care
Addressing browning requires an accurate diagnosis to implement recovery. If root rot is suspected, focus immediately on improving soil drainage. This involves incorporating organic matter like compost or grit into the soil to enhance aeration. In severe waterlogging cases, the shrub may need to be temporarily excavated and replanted on a slight mound to elevate the root crown.
Remedial watering is needed if drought or winter desiccation is the cause. Water the shrub deeply and infrequently, allowing the topsoil to dry slightly between applications to encourage deep root growth. Before the ground freezes in late fall, thoroughly soak the root zone to provide moisture reserves against cold, dry winter winds. To prevent future winter burn, consider erecting burlap barriers on the most exposed sides (south and west) to shield the foliage from intense sun.
If pest damage is the issue, treatment depends on the insect. For soft-bodied pests like scale or mealybugs, horticultural oil or insecticidal soap is effective, targeting the undersides of the branches. A strong jet of water can dislodge spider mites, especially when applied repeatedly. For fungal infections, prompt pruning of all discolored branches is necessary to reduce the source of spores.
When pruning, remove all brown tissue back to a healthy green branch. Exercise patience with winter-damaged foliage, as the buds may still be viable even if the needles are brown. For long-term health, apply organic mulch around the base of the yew, keeping it a few inches away from the trunk to prevent moisture buildup. If salt damage is visible, thoroughly leach the soil with copious amounts of water in the spring to flush the harmful salts away.