Cedar Decline

Excuse my language but, dammit! Decline is the word of this decade when it comes to trees and habitats. Tree decline is not a diagnosis for removal, we can invest in and save the increasing number of tree species (next post about this topic) suffering "decline". This takes investment and attention which if you're reading this, you've already invested your attention. Thank you!

about the tree...

The Easter Red Cedar (Juniperus virginiana) is a much loved indigenous tree and horticultural components of many a yard, park, city. This is a dioeceious tree so a tree either produces pollen-only flowers or ovary-only flowers. The leaves (also called needles and scales) are reddish brown in winter and a deep green during the growing season. The seeds are born in lovely, bluish berry-like structures. This species is found throughout eastern Canada and the USA. They grow slow, producing dense and chemically rich wood tissues making them resistant to most diseases and pests. It's why we line hope-chests and closets with cedar wood. They can live a very very long time, 100s of years and grow in some of the most inhospitable conditions. The oldest documented J virginianis dated at ~940 yo. WOW - the history that tree survived is beyond my little brain.

what's the decline doing and what's doing it

Symptoms are:

  1. off color due to browning of needles, sometime preceded by a reddish to purplish hue color-change in the early Spring,

  2. needle/leaf drop especially from inner canopy out to branch tips,

  3. cankerous lesions on stems.

This is the order of disease progression, typically. First needle color changes, drop, then possibly lesion formation.

Three fungal, pathogenic species have been identified with the disease (see citations below). One is a superficial infection, the other two can move into the wood from the leaf tissues. The fungi can be transmitted to a tree via rain, air, cutting tools, and insects.

treatment is complex but not complicated

The best time to treat is at the first signs of infection. The treatment uses an integrated pest management (IPM) or plant health management (PHM) approach which includes identification of the pathogen(s). Different chemistries work on different fungal species; a knowledgeable arborist will be able to identify which or how many of the disease types your tree has. Better yet, like me, they'll always test their knowledge by doing extra research annually to learn what has been learned. Some of the fungicides effective against cedar blight diseases are of fungal origin. Specifically, fungi found in soil and having commensal or mutualistic relationships with trees. So, if your soil has been sterilized by bad lawn/garden care practices then the reduced diversity and/or abundance of soil microbes = unhealthy plants. Poor soil biology = poor root health and poor plant immune function.

Supplemental watering your trees during hot dry weather is critical as is a bit of added water during dry warm winters. Sterile pruning of lower infected limbs and canopy thinning increases air and light (UV) movement through the canopy. Wounded tissues can spread disease - sterile technique is NOT an optional choice. Watering with drip or ground irrigation to avoid spreading the diseases moving via water into the canopy will also save money/water.


f you do water with above-ground irrigation, then water early mornings. Check the roots - are they girdling the trunk of the tree? If so, then the tree can't get adequate water, minerals, and nutrients throughout it's body and the trees' ability fight disease is reduced. You'll need an arborist who can do root surgery to help fix.

The causal agent of the decline is a combination of two or more; 1) climate change, 2) urban heat island effects (if in the urban setting), 3) pathogen attack, and 4) soil conditions. How does climate change cause decline in junipers and other trees?

The last couple of decades of increased drought and high temperatures (average day temps, avg night-time temps, exception bouts of heat) coupled by more frequent high rainfall events in the Eastern US make a perfect storm. Fungal diseases thrive in hot humid weather and can tr

avel well from splashing water. They are evolutionarily well-equipped to produce spores that can weather extreme temps and drought/wet cycles. They are reproducing in larger numbers and thus spread more rapidly and possibly producing mutations beneficial to their ability to infect new hosts. While at the same time, trees are struggling with every increasing water demands caused from higher temperatures and more frequ

ent drought. Couple that with being planted in turf treated with an abundance of pesticides and herbicides, sucks.

selected citations

Nnadi and Carter. 2021. Climate change and the emergence of fungal pathogens, PLOS.