Evergreen bushes are valued for their year-round green foliage. When the needles or scale-like leaves of a coniferous shrub turn yellow, red, or brown, it signals significant stress or damage. Evergreens naturally shed their oldest, interior needles gradually, a process often mistaken for a problem. True browning, especially on exterior branches or tips, indicates the plant’s ability to transport water or photosynthesize has been compromised. This distress can stem from environmental extremes, chemical imbalances, or biological attacks.
Environmental Stress and Water Imbalance
The most frequent causes of evergreen browning relate to atmospheric conditions that disrupt the plant’s water balance. This often manifests in late winter and early spring as winter desiccation, or winter burn. This physiological disorder occurs because evergreens lose moisture through transpiration even when the ground is frozen.
When roots are locked in frozen soil, they cannot absorb water to replace the moisture lost, creating a severe internal drought. Bright winter sun and strong, dry winds exacerbate this deficit, accelerating moisture loss from the foliage. Damage typically appears on the side of the bush most exposed to the sun and wind, such as the south or southwest face. Needles turn reddish-brown, with browning progressing inward from the tip as plant tissue dies from dehydration.
A similar water deficit occurs during prolonged summer or fall drought, leading to root damage and needle browning. Drought stress reduces the bush’s vigor, increasing susceptibility to secondary invaders. Symptoms often include general canopy thinning and needles that are off-color or brown at the tips. Sometimes, browning progresses upward from the bottom as the plant sacrifices lower branches to conserve moisture.
Intense summer heat and sun exposure also contribute to browning, especially when combined with low humidity or reflected heat from paved surfaces. Heat stress can overwhelm the plant’s cooling ability, leading to scorched foliage. Any environmental factor causing the rate of water loss to exceed the rate of water uptake will result in brown foliage.
Issues Within the Root System and Soil Chemistry
Problems originating beneath the soil surface can mimic drought signs, causing above-ground browning even when moisture is present. Poor soil drainage is a significant cause, as evergreens do not tolerate standing water around their root systems. Saturated soil lacks the necessary oxygen, which suffocates the fine feeder roots responsible for water and nutrient absorption. This lack of oxygen leads to root rot, often compounded by fungal pathogens like Phytophthora.
When the root system is compromised, it cannot transport water to the needles, resulting in wilting, yellowing, and browning symptoms identical to an underwatered bush. Examining the roots of a suspected plant will reveal dark, mushy tissue instead of the firm, white appearance of a healthy root system.
Chemical exposure, often called chemical burn, is another common culprit. Excessive application of high-salt fertilizers increases the concentration of soluble salts in the soil. This high salt concentration reverses osmosis, drawing water out of the roots and severely dehydrating the plant. The resulting damage often appears as uniform browning or necrosis on needle tips throughout the entire canopy.
Road salt used for de-icing can also cause chemical burn when it leaches into the soil or sprays onto foliage. The salt dehydrates the roots, causing browning typically restricted to the side nearest the road. Improper planting depth can restrict root growth or cause girdling roots, slowly choking off water and nutrients, leading to gradual decline and browning over time.
Biological Threats: Pests and Fungal Diseases
If environmental and soil issues are ruled out, browning may be caused by specific living organisms that attack the foliage or stems.
Insect Pests
Spider mites are tiny arachnids that feed on sap within the needles, causing the green pigment to disappear. This results in a characteristic stippled, yellowish-green discoloration that later turns bronze or brown. Spruce spider mites are cool-weather pests, active in spring and fall, often dormant during summer. Infestations, common on junipers and arborvitae, are frequently accompanied by fine, silken webbing on the twigs. Scale insects are another group of sap-suckers, appearing as small, immobile bumps on stems and needles, slowly draining the plant and causing discoloration and dieback.
Fungal Diseases
Fungal pathogens cause various diseases, including needle cast and needle blight. Needle cast diseases are spread by airborne spores that thrive in wet, humid conditions. Infection usually occurs on new needles, but visible browning symptoms often do not appear until the following winter or spring.
These diseases typically cause older, interior needles to turn yellow or purplish-brown before being prematurely shed. This leaves branches bare except for the newest growth at the tips. On spruces, signs of a needle cast infection like Rhizosphaeria include tiny, black fruiting bodies (pycnidia) visible in neat rows along the needle’s surface. Infections often start on lower branches and progress upward, making the bush appear thin and sparse.