Wednesday , July 20 2022

How to identify and prevent Southern Blight on apple trees

Sclerotium rolfsii

What is the name of a fungus that can infect hundreds of plant species and live on organic matter in the soil for years? A gardener’s nightmare!

In this case, the nightmare is called the southern plague or southern tribe. An insidious mushroom called Sclerotium rolfsii (also known as Athelia rolfsii) causes this disease. Among other things, it can quickly kill apple and crab apple trees, black walnuts and roses.

The name “sclerotium” is a giveaway for what makes this fungus such a successful pathogen. It produces small dormant structures, so-called sclerotia, which both live from organic matter and can infect plants.

Symptoms of apple and crab apple trees

As soon as you notice the infection of your apple or crab apple trees, it is too late to save them.

The lower base of an apple tree seedling with mycelium at the base.
Look for a network of white mycelium over the bottom and the lower stem or stem. Photo courtesy of the Florida Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Bugwood.org about CC 3.0.

Watch out for sudden wilting, the death of stems, and yellowed leaves that remain on the tree. These symptoms typically manifest in the heat of summer. The stems of your tree can turn brown and die near the bottom line.

A telltale sign is the network of white mycelium on the bottom and the lower stem or trunk. The mycelium creates the sclerotia, which are round, yellow or pink round objects with a diameter of at most 1/8 inch.

Southern plague on apple stem and roots. Medium blue background.
Southern plague on apple stem and roots. Photo courtesy of the Florida Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Bugwood.org about CC 3.0.

Trees usually die shortly after symptoms appear, although they can survive for a month.

How To Prevent Southern Blight

As with most other deadly apple diseases, it’s best to avoid the problem. And we don’t want to ignore it!

If you know that the southern plague was active in the area, do not plant a tree there. Common plants that can serve as an infection reservoir are: tomatoes, Soybeans, peanuts and clover.

Close-up of Sclerotium rolfsii in the Apetri bowl.
Sclerotium rolfsii grows in a petri dish. Photo via Shutterstock.

The obsession with hygiene can help prevent the southern plague. Since the fungus lives on dead plant tissue, remove all organic matter from the base of your tree. Part of this strategy is that no crop residues accumulate there. And make sure and control weeds under your tree.

To our knowledge, there are currently no chemicals registered that can combat the southern plague.

Your tree becomes more resistant with age

The only good thing is that your tree is less susceptible to aging. One to three year old apple trees usually develop the most severe infections of the southern plague.

The reason for this is that the bark becomes thicker as your tree ages. The fungus will have greater difficulty entering it to cause infection.

Geography can spare your tree

As the name suggests, the southern plague typically infects plants in the southern part of the United States. Northern growers are usually (but not always) spared from this plant killer.

Southern rot in apples is a particular problem in the Piedmont region in the southeast. (The long region extends from New Jersey to Alabama) And it has been reported in nurseries and commercial orchards in Texas.

Avoidance is your best choice

Since the southern plague is usually fatal to apple and crab apple trees, do everything in your power to avoid infection.

Do not plant apple trees in areas where this mushroom is known. And keep weeds and crop residues away from your trees.

Did you lose a tree from the southern plague or could you save one? If so, let us know your experience in the comments.


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