Navigating Common Vascular Fungal Diseases

Vascular fungal diseases are common to many species of trees and shrubs, and can cause major damage or death. Vascular systems of trees are made of two main parts: the xylem and the phloem, which move water, sugars, and minerals around the tree to where the are needed. A tree’s vascular system functions similarly to veins and arteries in people. When fungal spores enter a tree’s vascular system, they can reproduce and create clogs that disrupt the flow of water and nutrients. This leads to the death of parts or whole trees.

There are many fungal vascular diseases, but there are three that we see very commonly in our urban environments: Phomopsis, Sphaeropsis, and Cytospora. They often have similar symptoms, similar causes, and can be controlled in similar ways.

Phomopsis

Phomopsis is a vascular disease of plants caused by several species of ascomycete fungi in the genus Phomopsis. It can affect many species of conifers and hardwoods trees. It often infects trees and shrubs that are already experiencing stressors such as transplant shock, freeze injuries, insect feeding, excessive pruning, or drought. The spores of Phomopsis exist throughout our environment and only threaten trees and shrubs when they enter the vascular systems. Infections are common in shrubs and trees with dense canopies, where little light or wind reach. Thin bark also allows for easier disease entry.

Symptoms

While some species may show more obvious symptoms like wilting shoots tips, cankers on stems, and browning vascular tissue, some species show minimal symptoms. Cankers are usually found on smaller branches (under 4 inches in diameter), though it can infect trunks. Depending on the species of plant, cankers may appear as different colored patches on stems, sometimes showing fungal fruiting bodies in wet weather. Some trees and shrubs may show leaf spots or fruit blight. Sometimes, all you may see is canopy dieback, which can be caused by many issues. Determining the presence of a Phomopsis infection often comes down to laboratory testing.

Once inside a tree’s vascular system, the fungi reproduce by developing numerous small black pads of tissue that erupt through the bark to release spores, thus causing the disease to spread further. The cankers caused by this event destroy the vascular tissues of the branches, killing them.

Management

Trees infected with Phomopsis are often already suffering from underlying issues. It is important to address those issues where possible. Water trees and shrubs during drought and heat events. Mulch properly and only fertilize if nutrient deficiencies are present. Always sanitize pruning tools and use proper pruning methods. Avoid planting in compacted soils with poor drainage.

Manage infections by attempting to prune out infected branches. Be sure to sanitize pruning tools with 70% isopropyl alcohol between cuts so you don’t further spread the disease. Phomopsis will continue to reproduce throughout the growing season, so be persistent in pruning out infected branches. Removing infected material disrupts the reproductive process of the fungi.

You may be able to use fungicide applications to prevent the infection of newly emerging growth in the Spring. These applications will not cure already infected branches, but rather prevent the spread to new growth.

Sphaeropsis

Sphaeropsis is a plant disease caused by many fungi species in the genus Sphaeropsis. In Pines and other conifers, this disease is also often referred to as Diplodia Tip Blight (caused by Sphaeropsis sapinea, formerly called Diplodia sapinea). Diplodia is one of the most destructive disease of Pines in the Midwest. We most commonly see it on Austrian Pine, but it can also infect Scots Pine, Red Pine, and Mugo Pine. If not controlled, Diplodia can kill trees.  Sphaeropsis may less commonly affect Cypress (thuja) and Juniper species as well. It can also infect non-conifer tree and shrub species.

Symptoms

The most common symptom of Diplodia on Pines is the browning and stunted growth of needles on branch tips. If you look closely at those dead needles, you will find small black fruiting bodies at the base of needles and twigs. Be aware the Zimmerman Pine moth can also cause browning of needles and tip dieback in Pines. If you look closely, Zimmerman Pine Moth leaves behind tunneling holes and you can find larvae in clumps of sap. The presence of black fungal fruiting bodies on the needles indicates Diplodia Tip Blight. New branch tips are most vulnerable to infection in Spring when the new growth is just emerging. Spores release from fruiting bodes and are distributed by rain, wind, pruning tools, and animal movement. Infected cones are often major sources of spores.

In other species, Sphaeropsis can infect branches and cause cankers that can swell and exude sap. You may also see swelling and sap dripping from wounds in the trunk. This often leads to the death of branches or possible the whole tree if the trunk is infected.

Management

To avoid infection in the first place, keep trees healthy. Water during drought and heat events. Mulch properly and only fertilize if nutrient deficiencies are present. Always sanitize pruning tools and use proper pruning methods. Prune out infected branches to reduce spore loads and slow the spread of the disease. Make your cuts 6 – 8 inches below obvious infections. Be sure to sanitize between each cut so you don’t further spread spores. Be persistent in pruning out infected branches.

Pine branch tips can be protected from reinfection using 2 rounds of copper fungicide sprays in the Spring when new growth is emerging. Much like with Phomopsis, these treatments prevent further infection of new growth, but they do not cure existing infections.

Cytospora

Cytospora canker is caused by the fungus Leucostoma kunzei, which can be found existing on the bark of Spruces and other trees. It becomes a problem to them when the fungus in introduced to the vascular tissues of the tree via pruning wounds, insect feeding, storm damage, or snow or ice damage. Spores can be carried by wind, rain, insects, and animals. We most commonly find Cytospora canker in Colorado Blue Spruce, though it can commonly infect most all Spruce species, Hemlocks, and White Pines. Cytospora less commonly infects other species of trees and shrubs.

Symptoms

In Spruces, Cytospora is typically found in trees that are at least 15 years old and 20 feet tall. You will see cankers along branches that ooze sap. Often, it looks like the sap just burst out the side of branches or trunks with no other signs of injury. Infections typically start in the lower canopy and work their way up. Branches will die one by one from the bottom up. You may see needles turn brownish purple and then drop.

Management

Once a Spruce in infected, there is no cure. Use of fungicides to control Cytospora can cause more harm than good. The disease can be managed by pruning out infected branches and using good cultural practices to keep the tree healthy. Water during drought and heat events. Keep trees properly mulched. Always sanitize pruning tools between cuts. Fertilize only to correct nutrient deficiencies. Stay vigilant and prune out infected branches when you see them. If the trunk of your Spruce is infected, there are limited actions you can take. Treating your Spruce with a growth hormone regulator called paclobutrazol may strengthen your tree’s natural defense systems, thus slowing the spread of Cytospora. Avoid planting Colorado Blue Spruce in the first place. They are not native to Wisconsin and prefer well drained soil and non-humid conditions.

Beyond Spruces, Cytospora may infect other hardwoods and can be found in a wide variety of tree and shrub species. Cankers appear different depending on species, but typically show as patches of discoloration on branches. You may see fungal fruiting bodies when wet conditions are present. Control and management methods are the same. Prune out infected branches, making sure to sanitize between cuts. Keep trees healthy with proper watering and mulching practices. Avoid over fertilizing and over pruning.

Overview

Keeping trees healthy with good cultural practices will decrease infections of vascular diseases. Plant species that are less susceptible. Avoid planting in compacted soils with poor drainage. Use proper watering, mulching, and pruning practices. Only fertilize to correct nutrient deficiencies.

If you have an infection of a vascular disease, there is no cure. Prune out infections, sanitizing your tools between cuts. New growth can be protected from some fungal diseases with properly timed spray applications of fungicides. Often, the only way to determine which disease your tree has is to send samples to your local plant disease diagnostic clinic. Reach out to Tree Health Management for more advice on how to handle fungal vascular diseases on your property.