Wednesday , February 21 2024

How to manage root rot in fruit, nut and landscape trees and shrubs

Many fruit, nut and landscape trees can succumb to root rot caused by three types of fungi and a group of water molds (formerly considered fungi). These include the fungi Armillaria, Phymatotrichum and Xylaria as well as the water mold Phytophthora.

The trees show different symptoms of these different diseases.

In all cases, however, there is a stressful tendency for the trees to be so weak that they tilt or even break near the bottom line.

There is no easy cure for any of these diseases. Trying to prevent it is your best bet. So keep reading to learn more about these troublesome diseases so you know what to look for.

Phytophthora Root Red

Phytophthora Species prefer moist soils so much that they are known as water forms. The notorious kind Phytophthora infestans caused the famine in Ireland in the late 19th century and the death of a million Irish.

Despite this term, they are now divided into a separate kingdom (the Oomycetes) and are no longer considered mushrooms. However, they behave like them!

An apple tree that loses leaves due to Phytophthora root rot infection.
Photo by H.J. Larsen, about about CC 3.0. Circumcised.

A large number of these organisms cause root rot in a variety of plants. In trees and shrubs, however, the species is mainly responsible for root rot Phytophthora cactorum.

While you might expect this type of root rot to be a problem only in wet areas, vegetation in dry areas can also be vulnerable. Irrigation can lead to damp soils and increase susceptibility to this type of root rot.

These organisms have two types of spores. Oospores are thick-walled spores that lurk in the ground for a long time and can strike in damp conditions. Other types of spores (zoo spores) can swim so that they can move across the ground in irrigation water or drainage. This allows them to quickly infect a large number of trees.

Phytophthora root rot in nursery stands that are grown under unfavorable conditions.
Photo by Edward L. Barnard, Florida Department of Agriculture and Consumer Services, about CC 3.0. Circumcised.

If your tree or shrub only suffers from Phytophthora root rot and not from the other types of diseases it causes (The collar and crown will rot) there is a possibility that it can recover. This can happen if the conditions become unfavorable for the pathogen, e.g. B. warmer and drier.

How to tell if the roots of your apple tree are infected by Phytophthora

So many factors can lead to a decline that it can be difficult to determine what is causing these symptoms. If you think your tree could be under siege PhytophthoraDig out the soil around the roots and look at the fine ones.

They could be orange or brown, and the primary roots could shed the fine ones. In contrast, roots that drown due to damp soil are generally brown and may smell decayed or fermented.

Cultural controls

1. Monitor irrigation water

The use of sprinklers can spread quickly Phytophthora on trees. As an example of how dangerous irrigation canals can be, scientists isolated 749 specimens from irrigation canals in eastern Washington State. The way to check the water for these organisms is to hang fruits in them and look for visible fruit rot.

2. Limit the saturation of the soil

Monitor your soil moisture and water it only when necessary, as free water significantly increases the likelihood of this pathogen spreading.

3. Plan ahead if you know Phytophthora is near you

Try planting in well-drained soil. In fruit and nut trees you can sometimes find rhizomes that are resistant to this pathogen.

However, the resistance in rhizomes varies depending on the species of Phytophthora. So make sure your soil is tested to determine the exact type before choosing a variety to plant.

4. Biologicals and biopesticides

Fortunately, microbes in the ground are constantly waging war against one another, and you can use this trend to your advantage.

Many types of soil bacteria and fungi can outperform root rot organisms. For example a classic Organic control mushroom that is common is Trichoderma.

You can promote the growth of such organisms by adding a lot of organic material to the soil. Grass cutting and compost are a good start.


Only certain compounds act on Phytophthora, since they are not real mushrooms.

Treat the entire area for the root zone and not just near the tree base with the following compounds:

The stem and root zone sprays that should not be combined with a copper spray program include:

  • Phosphoric acid, salts of mono- or di-potassium
  • Fosetyl Al

Armillaria Root Red

The honey mushroom or the smallest mushroom, Armillaria melleaalso threatens a large number of plants. Not only does it occur in a large number of soils, it also has a very wide range of hosts.

It is really a giant mushroom – its mycelium can spread for miles – making it the largest organism in the world.

Black rmillaria mycelium strings on a tree trunk.
Armillaria mycelium cords can extend for miles. Photo via Shutterstock.

And to make matters worse, the mycelium can survive for decades in dead root tissue and stumps. Stone fruit is the most vulnerablewhile apple trees are moderately vulnerable.

How to tell if your tree has Armillaria root rot

Symptoms can range from obviously terrible symptoms like the sudden collapse of the tree in the middle of summer to more subtle symptoms. The growth of your tree’s final shoots may be reduced and the leaves may turn purple much earlier than they should.

You can diagnose Armillaria root rot by checking the base of your tree underground. The wood can show white rot. If you remove the outer bark from the roots, they may look spongy and thread-like (hence the name mushroom).

If the tissue actively breaks down, the mycelium can be bioluminescent. Another giveaway can be the production of honey-colored or light brown tufts of mushrooms at the base of the tree.

It may be too late for your tree

It is best to try to avoid this fungus. Try to remove all pieces of wood and roots from the ground before planting your tree, as the fungus lives on in dead tissue.

Also try to protect your tree from stress. Adjust the pH of the soil and grow cover crops.

The degree of variation in this fungus can make it difficult to choose a resistant root type. A rhizome that is resistant in one test can be susceptible in another test.

Black root rot

As if the previous types of root rot were not bad enough, there is another type of root rot that affects older apple and hardwood trees such as walnuts and elms. Two types of mushrooms, Xylaria mali and Xylaria polymorphacause this disease.

Black root rot is also known as the dramatic name of the dead man’s fingers because it creates structures that look like blackened fingers. These can be found on decaying root surfaces.

The dead man's fingers, Xylaria polymorpha, grow structures on a leaf-covered forest floor.
Look for “fingers of the dead” to see signs of xylaria infection. These can be on the tree or growing nearby from the ground (from the roots).

Although trees of all ages can infect with this infection, those who die are usually at least 10 years old.

Since the fungus can live on root fragments for up to 15 years after removing the infected tree, you cannot plant another apple tree at this point. However, if the site has deep soils and is well drained, you can plant peach trees as they are not susceptible.

Cotton root rot

Cotton root rot is a devastating disease that is also known as the Texas Root Rot or the scientific name Phymatotrichum Root Rot.

The species name of this mushroom, Phymatotrichum omnivorumtranslated means “eats everything”.

Phymatotrichum root rot (Phymatotrichopsis omnivora)
Photo by S.D. Lyda, about CC 3.0. Circumcised.

This is an appropriate name for the fungus, as it can affect more than 2,300 types of deciduous plants. Oddly enough, it can infect any type of fruit tree except pomegranates.

Fortunately, for most fruit tree growers, this aggressive fungus only occurs in soils that are heavy and alkaline – as is common in the Southwest – and in soils that are below 5,000 feet.

Cotton root rot attacks when the soil is warm and damp – typical weather after the monsoon. The fungus spreads when an infected root touches an uninfected one. To complicate matters, Texas Root Red can survive indefinitely on native vegetation such as mesquite trees.

The mushroom can also attack its hosts indiscriminately. For example, cotton root rot fungi from cotton can infect apple trees. This is a particular problem because many residential areas in the southwest are on old cotton or lucerne fields.

Even worse – the dormant structures of the fungus survive for many years in soils more than 12 feet deep.

How to tell if your tree has cotton root rot

The only way to positively identify this infection is in a laboratory. However, you can make a good guess based on the symptoms and the knowledge that the fungus is active in your region.

Your tree can suddenly wither in the heat and leaves (dead or dying) remain attached to the tree even after it dies. The branches can wither permanently as early as two weeks after the first signs of the disease appear.

Your tree is probably a goner because there are no good controls for cotton root rot – although the fungus has been studied since 1888.

You may be able to save your tree

If you notice the infection early enough, there is a chance to save your tree.

Treat the floor aggressively first. Add large amounts of ammonium sulfate and soil sulfur, and then pour deeply. The idea is to lower the pH of the soil when these fertilizers get into the deep soil.

This serves two purposes. One is to inhibit the fungus, and the other is to promote soil microbes that may be able to control phymatotrichum.

If this technique is successful, you will need to repeat it every year. If not, the soil returns on favorable terms for the mushroom, which will return with all its might.

If you can’t save your tree, at least the soil will be ready to plant next year – hopefully with a hardy tree.

Read more about the prevention, identification and treatment of cotton root rot here.

All types of root rot can be fatal

Prevention is the best choice in all cases of root rot. Make sure you plant your apple tree in well-drained soil to protect it from Phytophthora root rot. Minimizing the amount of moisture in the soil can help protect against this water mold.

Likewise Treat your soil with bio-control agents Applying cultural practices that promote the growth of these types of soil organisms can be helpful in the fight against root rot in Phytophthora.

If you know Armillaria root rot has occurred in your area in the past, prepare for planting by plucking old tissue such as pieces of wood and dead roots from the ground. The fungus can live in these tissue types for years. Protecting your tree from stress can help keep this fungus at bay.

Tree roots infected with root rot.

Although there are some fungicides that can limit Phytophthora infections, there is not much you can do if your tree shows symptoms of Armillaria, Salsify, or Cotton Root.

Have you waged war against root rot in your fruit, nut or landscape trees? If so, let us know how it went in the comments below so we can learn from your experience.

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