The sudden browning or decline of an evergreen bush is often alarming to property owners. Evergreens are resilient, but their persistent foliage means they constantly lose water, making them susceptible to various stressors. Diagnosing the exact cause requires examining the plant’s history, environment, and physical symptoms. Checking the most common causes helps identify whether the issue is related to soil, insects, weather, or disease.
Root Health and Water Management Errors
The most frequent causes of evergreen decline relate to planting and water management. Planting a bush too deeply is a common error that smothers the root flare—the point where the trunk widens at the base—restricting oxygen flow. Roots require oxygen for respiration, and when suffocated by excessive soil or compacted earth, they die, leading to symptoms like yellowing or browning foliage.
Conversely, both overwatering and underwatering lead to similar symptoms of desiccation because the roots are unable to function properly. Chronic overwatering causes fine feeder roots to rot, preventing the bush from absorbing water even when the soil is wet. This excess moisture creates an anaerobic environment where oxygen is displaced, effectively drowning the root system.
Deep, infrequent watering is preferred for established evergreens, encouraging deep, drought-tolerant roots. To check for adequate moisture, perform a finger or trowel test six to twelve inches below the soil surface. If the soil at that depth feels dry and crumbly, the bush needs a thorough soaking. If the soil remains soggy days after watering, the issue is likely poor drainage, which must be corrected to restore oxygen to the root zone.
Common Insect Pests and Damage Signs
Certain insects specialize in attacking evergreen foliage and stems, leaving behind distinct evidence of their presence. Spider mites are tiny arachnids that thrive in hot, dry conditions and feed by piercing plant cells to suck out the contents. Their feeding causes stippling, a characteristic damage appearing as thousands of tiny yellow or bronze dots on the needles.
When mite populations are high, they spin fine, silk-like webbing, especially between the needles and small twigs. To confirm an infestation, hold a white sheet of paper beneath a branch and tap it sharply; if mites are present, tiny specks will fall onto the paper and begin to crawl.
Scale insects are sap-sucking pests, stationary in their adult stage, appearing as small, immobile bumps on the stems and needles. They excrete a sugary waste product called honeydew, which often leads to the growth of sooty mold, a black, crusty layer on the branches below the infestation.
Borers are the larvae of certain beetles or moths that tunnel beneath the bark, disrupting the flow of water and nutrients. Signs of their activity include small, round or D-shaped exit holes in the trunk or branches and the presence of sawdust-like material, known as frass, often mixed with oozing pitch or sap.
Environmental Stress and Seasonal Injury
External factors like extreme weather and chemical exposure can cause evergreens to brown, often exhibiting a pattern that helps identify the cause. Winter burn, or desiccation injury, occurs when the ground is frozen, preventing the roots from absorbing water, while the foliage loses moisture on sunny or windy winter days. Symptoms typically appear in late winter or early spring as browning on the side of the bush facing the prevailing wind or the intense winter sun.
Road salt damage presents in two forms: salt spray and soil absorption. Salt spray from nearby roads or sidewalks causes browning and dieback concentrated on the side of the bush nearest the salt source. Excessive salt absorbed through the roots causes a more uniform yellowing or browning of the needles across the entire plant.
Accidental exposure to chemicals is another source of injury, most often from herbicide drift, which occurs when weed killers are applied nearby on a windy day. Herbicides can cause discoloration in distinct patterns, such as a spiral of dead needles or a sudden, uniform browning of the foliage where the chemical mist landed. These injuries appear suddenly, making the diagnosis straightforward by linking the damage to a recent event.
Fungal Diseases and Pathogen Identification
Fungal diseases are caused by pathogens that thrive in specific environmental conditions. Needle Cast is a common fungal infection, typically affecting pines, firs, and spruces, where the fungus infects new needles but symptoms are not visible until the following year. This disease is characterized by the browning and premature drop of older, interior needles, while the newest growth remains green. Close inspection of infected needles may reveal tiny, black, pimple-like structures called pycnidia, which are the fungal fruiting bodies.
Phytophthora Root Rot develops when evergreens are subjected to prolonged periods of saturated soil. This water mold destroys the root system, causing the foliage to wilt and turn brown even when the soil is wet, indicating non-functional roots. When affected, the roots appear dark, soft, and decayed, lacking white feeder roots. Management requires correcting the underlying water issue to halt the spread of the pathogen and sometimes applying specific fungicides.