Plant Problem Diagnosis Key / Diseases

Disease

Elm yellows (phloem necrosis)

Candidatus Phytoplasma ulmi

A phytoplasma spread by leafhoppers that kills the inner bark of American and red elm. The whole crown usually yellows and the tree can die within a year. There is no cure.

Elm yellows: the whole crown thins and yellows at once
Elm yellows: the whole crown thins and yellows at once Photo: NatureServe, CC BY 2.0, via Flickr

Signs

What favors it

American, red and winged elm; spread by leafhoppers and through root grafts between elms growing close together.

Prevention

Crops it shows up on

Shade & ornamental trees.

Often confused with

DiseaseDutch elm disease PestElm leaf beetle Growing conditionsConstruction and root damage

Sources

Why →

Treatment by crop

Cultural, biological and chemical options in the order to use them, and notes written for each crop.

Identification is free. Treatment is on the Home and Pro plans.

Open in the key See plans

Questions in the key that lead here

  1. Look the plant over, leaf undersides included. Are insects, mites, slugs, eggs, webbing or droppings on it?
    No, only damage or discoloration
  2. Where is the problem?
    A tree or shrub
  3. Which part of the tree or shrub shows the problem?
    Branches dying, or the crown thinning
  4. How is the dieback showing?
    Slow thinning from the top down, over a year or more
  5. Look at the base of the trunk, where it meets the ground.
    An elm: the base looks normal, but the whole crown yellows and drops in a few weeks

Not a match? Start the key or describe what you see.

More from university Extension: search Extension pages on elm yellows, or find a plant diagnostic lab through your state's Extension.

Other diseases

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