Botryosphaeria Canker: An Infection of Trees and Shrubs

Botryosphaeria Canker: An Infection of Trees and Shrubs

In today’s TrueTreeTalk post, we explore Botryosphaeria canker, an infection of trees and shrubs.  We look at its classification, conditions for infection, ways to reduce the likelihood of infection, and more.

How is Botryosphaeria Classified?

Taxonomy can be difficult to understand.  It can be even more so with fungi with so many variables and new information updating things.  Given this, we’ll try our best to explain how Botryosphaeria are classified.

Botryosphaeria is a fungus.  It belongs to the order Botryosphaeriales and the family Botryosphaeriaceae.  The genus for Botryosphaeria is Botryosphaeria, however it is the sexual stage of the genus.  There are a number of genera that are classified as asexual stages of it depending on their characteristics and how they produce spores.  Some of the asexual stage fungi are Sphaeropsis, Dothorella, Diplodia, Fusicoccum, and Macrophoma.  They can be seen as different stages of the same thing.  In looking at Botryosphaeria here, we are looking at the sexual stage.  Within the genus Botryosphaeria, there are many species.  Here we are looking at them all as a group and refer to them as Botryosphaeria.

What Kinds of Plants does Botryosphaeria Infect?

Some fungi are specific to a host.  They infect one kind of plant.  Although there are some species of Botryosphaeria that attack specific hosts, many more are general.  These generalist species will infect a wide variety of shrubs and trees.

One thing about Botryosphaeria is that it is opportunistic.  It attacks plants that have low vigor and are stressed.  This is an important idea we will get to later.

What are Some Symptoms and Signs of Botryosphaeria Canker?

Symptoms include leaves that suddenly turn brown and leaves not coming out in spring, though symptoms vary between hosts as well as by what underlying stress the plant may have.

Signs can range from small to widespread depending on the severity of the infection and the stress of the plant.  Bark and sapwood can die, shoots can girdle, the trunk can have cankering, and branches can dieback.  If severely infected, a plant can produce a large amount of epicormic growth, and the bark can change color and fall off.  There can be dark lesions that are sunken and have sap that oozes.

In some cases, a plant can look healthy overall but will have leaves that wilt and branches that die back.  One of the early signs of the disease can be leaves that yellow on only one branch while the others on the plant seem fine.  Once a section is girdled by the fungus, leaves can turn yellow and die, there can be wilting, and leaves can drop.  The amount of canopy deadwood can increase.

If you were to remove the bark from an infected branch, the color underneath would be brown to red/brown rather than white.  The same could also be seen if an infected branch were pruned away.

Cankers can look like they are darkened, sunken wounds.  They can also be covered and contained by wood that has callused over the wound.  This can be more prevalent on branches that are larger and on trunks.  Bark can also peel away from areas with cankers.  If the bark is smooth, the cankers can look like blisters.  On trees that produce gum, like sweetgum, cankers can exude gum.

How Does Botryosphaeria Enter Plants?

Botryosphaeria enters plants through openings such as wounds, lenticles, and cracks caused by growth.  It can enter through wood that has died and spread to living wood.  The fungus can be spread by air, by water splashing on it, insects, and by tools used for pruning if they are contaminated.

Does Botryosphaeria Harm Plants Right Away?

Certain species of Botryosphaeria can live in a plant without causing harm for an extended period of time and will begin to cause damage once the plant is sufficiently stressed by other things.  When something lives in a plant with benefit to the plant or without harming the plant (like Botryosphaeria before the infection causes damage) it is called an endophyte.  One consequence of this is that plants can die quickly if they experience significant stress and have the infection inside of them.  It can take time for cankers to show signs.  They can be in a plant for a significant amount of time, up to years, before anything is seen.  

The fungus can also live in dead branches that have fallen from a plant and overwinter in tissue that has died.

How does Botryosphaeria Canker Harm Plants?

Cankers can prevent minerals and water from flowing past the point of infection.  Cankers are dead plant tissue.  The vascular portion of the tissue underlying them is also dead.  Cankers girdle sections of trees.  Once they do, the leaves past the girdle to the tip of the branch or stem wilts, then becomes yellow, and finally brown.  Girdling can cause bark to die and then fall from areas with cankers.  The leaves wilt and branches die.  The wood on the bark changes from a light color to brown or black.  Cankers can ooze depending on the tree. 

What Kind of Stresses Increase the Likelihood of Botryosphaeria Canker Infection?

Stress from a number of sources can leave plants vulnerable to being infected with Botryosphaeria canker.  Things like drought, heat, freezing, insects, incorrect pruning, improperly applied mulch, incorrect planting, and more can all negatively impact a plant.

Are There Ways to Reduce the Likelihood of Botryosphaeria Canker Infection?

The likelihood of Botryosphaeria canker infection can be reduced.  As we mentioned, most Botryosphaeria species are not host specific and instead infect plants that are weakened through stress.  By reducing stress, the likelihood of infection can be reduced.

Ways to reduce stress include giving plants the specific conditions they need, avoiding injury to plants, practicing good sanitation around your plants, buying healthy plants in good condition, growing plants suited for your climate and zone, providing proper irrigation, providing protection from large and sudden temperature drops, proper fertilization, and pruning away dead wood.  These steps can improve the overall health of your plants and can be one of the best ways to reduce the likelihood of infection from Botryosphaeria.  Unfortunately, fungicides don’t necessarily work well against Botryosphaeria, though there are some that can suppress it.

If you found learning about Botryosphaeria canker helpful, check out our other posts on our TrueTreeTalk blog.  Follow us on Facebook to keep up with these and other posts.

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