Hello,

Thank you for reaching out to Ask Extension with your question.

Dead branches in the interior of a cypress tree can be caused by several factors. In many cases, it is simply a normal part of the tree's growth. As the tree matures, the dense outer canopy shades the older interior branches, causing them to die back naturally. However, dead branches can also be a sign of disease or environmental stress.

Here are a few possibilities to consider:

Natural self-pruning
If only the older interior branches closest to the trunk are brown while the outer foliage remains green and healthy, this is typically normal. Limited sunlight reaches the inner canopy, and the tree sheds older growth.

• Recommendation: Dead interior branches can be pruned out at any time to improve airflow and reduce the accumulation of dead material.

Fungal cankers (such as Seiridium or Botryosphaeria)
If entire branches are turning brown and you notice sunken areas on the bark, cracked bark, or resin (sap) oozing from branches or the trunk, a fungal canker may be the cause.

• Recommendation: Prune affected branches several inches below the damaged area. Disinfect pruning tools with rubbing alcohol or a 10% bleach solution between each cut to help prevent spreading the disease. If cankers are present on the main trunk, the long-term health of the tree may be compromised.

Needle blight
If browning begins on the lower branches and gradually moves upward, a needle blight disease may be involved.

• Recommendation: Remove dead or heavily affected branches and avoid overhead irrigation, which can encourage fungal diseases. Fungicides are sometimes used in severe cases, but they are generally most effective when applied preventatively and are best considered after a positive diagnosis.

Crowding or root stress
Poor air circulation, planting trees too closely together, overwatering, poor drainage, or mulch piled against the trunk can all contribute to decline.

• Recommendation: Make sure the tree receives adequate water during dry summer periods while avoiding saturated soils. Cypress trees prefer well-drained soil, and mulch should be kept several inches away from the trunk.

Wildfire considerations

Since you mentioned concerns about wildfire, removing dead branches from the interior of the tree is a good practice. Dead material can contribute to ember ignition and increase fire risk. Pruning out dead branches, maintaining good spacing between trees, and removing dead needles or other accumulated vegetation beneath the trees are all recommended steps for creating a more fire-resistant landscape.

It appears from your photos that the dead branches are all located in the interior of the tree which makes me lean more towards natural self-pruning than a significant health issue. The photo showing the row of trees from a distance appears healthy, although somewhat crowded. None of the photos showed the trunk or branches close enough for me to be completely sure there is no excessive sap or sunken bark so do double check and send over photos if you see anything of that nature.

You may also find these Oregon State University Extension publications helpful:

• Keeping Your Home and Property Safe from Wildfire

• Managing Insects and Diseases of Oregon Conifers

Best regards,

Hilary Jensen

Master Gardener and Community Horticulture Coordinator

Wasco County

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