Evergreen pines are some of the most resilient tree species on the planet, but that doesn’t make them invincible to diseases.
Fungal spores are the cause of most diseases and can easily spread between individual trees.
Read the list below to better understand the most common diseases that affect fir trees along with how to identify and treat them.
1. Swiss Needlecast
This disease is specific to Douglas fir trees and is caused by fungal spores that spread throughout the canopy during rainy weather.
You will notice it on the younger growth first because older needles are less susceptible to infection.
Symptoms include chlorosis of the needles that begin to fall off prematurely, lack of vigor, and other abnormalities in its growth.
Examine the needles, and you’ll see they are covered in tiny black and brown spots.
Remove affected growth, and destroy it. Spray a fungicide to reduce the chances of it spreading to other trees.
Treating large-sized trees can be difficult and ineffective, so they may not be worth treating. If this disease isn’t stopped, the tree will completely defoliate and eventually die.
2. Rhabdocline Needlecast
Only affecting Douglas fir trees mainly in the late summer and fall seasons, Rhabdocline needlecast affects new growth the most.
As spring comes around, this fungus will cause the needles to burst, thus spreading its spores onto more of the canopy and circulating them through the air.
Light yellow and red needles will appear in the late summer and fall. It will be most prevalent in the newest young growth as older needles are rarely affected.
Remove and destroy any affected branches to prevent the further spread of the spores and complete tree death.
Fungicide is helpful in mitigating its spread, especially when applied before bud break in the spring.
3. Twig Blight
Mainly affecting silver fir and Douglas fir trees, twig blight will cause new shoots to grow abnormally and eventually dry and brown.
It rarely affects older mature growth, but the spores can remain on the older stems and transfer to the young new growth.
New growth will be curled or stunted, eventually turning dry and brown before dying.
Twig blight will only affect the newest twigs, so be sure to remove any branches that are infected and destroy them to prevent the spread.
Reduce the amount of moisture in the area, and increase air circulation as much as possible. Don’t plant trees too close to one another, and ensure the soil has good drainage.
Most trees will recover in the spring after the tree begins to grow again.
4. Sudden Oak Death
The majority of the foliage will turn brown simultaneously and lead to sudden tree death. This fungus is most common along the West Coast but will affect multiple species of trees in different locations.
Shoot tips will begin to die back, and wilting new shoots will be noticeable. Sudden browning of the leaves and eventual leaf drop are the most evident signs.
Plants nearby can carry and transmit the disease without it being lethal to the plant. Phytophthora is always better managed by ensuring the area has good airflow and the soil drains efficiently.
In most cases, this disease will suddenly kill your tree.
5. White Pine Blister Rust
Mainly affecting white pine trees, this disease will kill the tops of trees or the entire tree fairly quickly. This disease needs to infect both a white pine tree and a currant or gooseberry to complete its lifecycle.
White pine blister rust is easily identifiable by full branches of needles turning yellow and then transitioning to rusty red with cankers on the affected branches.
Blisters will form near the cankers in spring and release powdery orange spores.
Remove any affected branches as quickly as possible.
In many cases, this will cause tree death, but in areas where spores can not complete their life cycle (missing currant or gooseberry), the tree will be severely affected but may continue to live on for some time.
6. Melampsora Needle Rust
Affecting many different species of poplars, pines, gooseberry, currants, and more, Melampsora needle rust can spread quickly through the different spore life cycles.
It has alternate host species of black cottonwood, aspen, and poplar trees.
Necrosis of leaf tissue is the most noticeable symptom. Black, red, or yellow needles will be present among dying and browning needles. Small rust-colored fruiting bodies can be seen on the needles.
Remove affected branches and fallen needles on the ground. Preventative fungicides are the most helpful in reducing spores and the spread of the disease.
This needle rust will result in defoliation, and excessive defoliation will lead to tree death.
7. Pucciniastrum Needle Rust
This fungal disease comes from spores transferred by infected trees and alternate hosts like huckleberry, wild blueberries, and cranberries. This species requires an alternate host of the Vaccinium genus to complete its life cycle.
Small white tubules will form on affected needles near yellowing areas or on all needles. Necrosis of needles that have grown this current year and yellow banding are prevalent symptoms of this disease.
Prevent this disease by spraying protective fungicides on new and developing shoots since they are the most susceptible. If the tree is not able to grow new shoots, its health will begin to decline, and it will eventually die.
8. Uredinopsis Needle Rust
The bracken fern is an alternate host for this rust disease, causing the rust to spread among many understory trees.
Symptoms include yellowing blotches on the tops of both old and new needles. White tubules of fruiting bodies on the underside of the needle are also common when infected.
Remove bracken ferns or use an herbicide to keep them from growing. Trimming and destroying all affected branches and trees is also important to ensure the tree keeps some of its needles. If it loses too many needles, it will die.
9. Annosus Root Rot
This disease is caused by a fungus that thrives in old stumps and dead wood. The fungal spores are transferred through the soil as well.
If the interior of the tree shows signs of dead wood or black spotting or if white fungal fruiting bodies are noticed in dead or dying wood, the tree is likely infected.
This is most common in tree farms. After trees are cut, the fungal bodies make a home in the dead stumps left behind. Removing these stumps or treating them is important to prevent the spread of this disease.
10. Phytophthora Root Rot
Phytophthora root rot is caused by fungal spores that live and spread in moist soil.
If infected, you may begin to notice that the tree has stunted growth or is growing irregularly. An infected tree can also show dieback beginning from the base of the tree.
Cankers may be present near the base of the tree along with dead branches.
If you gently excavate the roots, you may find black spotting or rotting root tissue. This is one of the most common symptoms since it is a root rot disease.
Ensure the soil is not overly saturated, the area drains quickly, and sprinklers are not directly hitting the lower branches and trunk.
Without roots, a tree can not survive, and the more the disease persists, the more roots will rot and the less likely the tree is to survive.
11. Interior Needle Blight
Caused by multiple fungal species
Limited to true fir species, this fungal disease can affect all trees but will focus on the older growth.
Old and low interior needles and branches will be affected the most since the air circulation is minimal and spores can fester in the dark.
Identifying this disease is difficult because it looks similar to regular dieback from new growth and drought conditions. You should be able to notice small black fruiting fungal bodies on the underside of needles.
Increase air circulation by pruning low branches that touch the ground. If needed, apply fungicides in affected areas and unaffected areas to prevent the spread.
Most of the time, the tree will recover with proper treatment and care.
Cankers can be devastating to all species of trees. They are spread by fungal bodies and can cause large growths on the tree trunks and branches.
You may notice some dieback and yellowing of branches, which then leads to the identification of a large overgrowth or open wound on the wood.
Oozing sap or fruiting bodies that are black, gray, or brown can be seen within the canker.
Remove and destroy any materials affected, and do not plant in the vicinity of the affected area of trees.
Trees will begin to die if infected with a fungal body that leads to a canker. It is best to remove them rather than wait for them to die because they can spread the spores while they are still present.
Fir trees are resilient, but fungi are more resilient! Work toward giving the trees ample air circulation, reduce the wounds you create on a tree, and pay attention to your trees.
Many times, catching this early on will lead to disease mitigation and long life for the tree.