A sudden change in the color of a cypress tree’s foliage, such as the popular Leyland or Arizona cypress, from green to brown can be alarming. Browning is not a disease itself, but a visible symptom that the tree is under stress. Determining the precise reason requires careful observation, as the location and pattern of the browning often provide the most reliable clues for diagnosis. This guide differentiates between the most common environmental, biological, and natural factors that cause cypress foliage to turn brown.
Water Imbalances and Environmental Stress
The most frequent cause of cypress browning relates directly to the tree’s water supply and surrounding environmental conditions. Cypress trees require consistently moist soil, and any deviation from this balance can quickly manifest as foliage discoloration. Water stress affects the tree’s ability to transport nutrients and maintain cell turgor, leading to desiccation.
Drought stress, or underwatering, typically causes browning to start at the tips of the branches or on the top part of the tree, progressing inward and downward. The foliage becomes dry and brittle as the tree sacrifices it to conserve moisture. Checking the soil moisture several inches down is important, as surface watering often fails to penetrate deeply enough to meet the tree’s needs.
Conversely, overwatering or planting in poorly drained soil can also cause browning due to root suffocation. When roots sit in saturated conditions, they cannot take up oxygen, leading to root decay and an inability to absorb water, ironically mimicking drought stress. This type of browning often starts on the lower branches and appears more diffuse throughout the tree. Other stressors, such as transplant shock or chemical damage from fertilizer burn or road salts, can also induce browning by damaging the root system or foliage directly.
Insect Pests and Mite Infestations
Tiny pests that feed on cypress foliage can lead to widespread browning, as their feeding activity damages the cells responsible for the tree’s green color. Spider mites are a common culprit, especially during hot, dry periods when their populations explode rapidly. These arachnids suck sap, causing the foliage to develop a fine speckling or stippling that eventually turns yellow, then brown.
A fine silk webbing, often visible between the branchlets, is a signature sign of a heavy spider mite infestation. A simple shake test over a white sheet of paper can reveal the presence of these minute pests.
Another specific pest is the cypress tip miner, a moth larva that tunnels within the growing points of the shoot tips. This internal feeding causes the tips of the twigs to turn yellow and then brown, often becoming noticeable in late winter or early spring. Scale insects, appearing as small, stationary bumps on stems and branches, also feed on sap, which can cause foliage to yellow and eventually turn brown.
Fungal Diseases and Root Pathogens
Infectious agents, particularly fungi, cause browning patterns that are often localized and distinct from environmental stress. Canker diseases, such as those caused by Seiridium or Botryosphaeria fungi, are progressive issues for many cypress species. These diseases create sunken, discolored lesions, or cankers, on the branches, twigs, or trunk.
The cankers girdle the branch, cutting off the flow of water and nutrients, which causes the foliage beyond the canker to rapidly yellow and turn reddish-brown. This localized dieback is often referred to as “flagging” because a single, scattered branch or section turns brown while the surrounding foliage remains green. Seiridium cankers are frequently associated with a thick, sticky resin oozing from the infected bark.
Another biological cause is Phytophthora root rot, a water mold that thrives in poorly drained or saturated soil. This pathogen attacks the fine roots, compromising the tree’s ability to absorb water. The above-ground symptoms resemble severe drought, with foliage becoming dull, bronzed, and then light brown as the entire tree declines. If the bark is removed near the soil line, the inner wood may show a reddish-brown discoloration extending up from the roots.
Natural Shedding and Species-Specific Behavior
Not all browning indicates a problem; sometimes, it is simply part of the cypress tree’s normal maintenance and growth cycle. Most evergreen cypress varieties, including Leyland cypress, undergo a process called inner needle drop or seasonal shedding. They naturally shed older, interior foliage that is no longer receiving adequate sunlight, typically during the fall or early winter.
This natural browning is uniform within the canopy, affecting only the oldest needles near the trunk and main branches. The outer growth and branch tips remain vibrantly green, distinguishing this process from distress browning, which often starts on the outside or tips of the branches. If the browning is confined to the inner parts of the tree and occurs cyclically, it is likely a normal, non-threatening process.
A few cypress species, most notably the Bald Cypress (Taxodium distichum), are deciduous conifers and are expected to turn russet-brown in the fall. This species drops all of its needles before winter, similar to a maple or oak tree, which is a species-specific behavior and not a sign of sickness. Observing whether the discoloration is patchy or uniform, and whether it affects the interior or exterior foliage, will help determine if the tree is in distress or merely self-pruning.