DiseaseHigh Severity

Elm Phloem Necrosis (Elm Yellows)

Phytoplasma (bacteria-like organism)

A systemic disease of elms caused by a phytoplasma, also known as elm yellows. Formerly called elm phloem necrosis in the U.S. and witches' broom in Europe. The disease causes degeneration of phloem and cambium, resulting in tree death.

Peak Season: Symptoms appear July-September, death by end of growing season
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Elm Phloem Necrosis showing characteristic yellowing and wilting

Identification & Symptoms

What to Look For

Rootlet necrosis followed by phloem and cambium degeneration
Inner phloem and outer wood turn lemon-yellow to butterscotch brown
Faint odor of oil of wintergreen (methyl salicylate) from discolored areas
Leaves droop, curl, turn bright yellow then brown
Premature defoliation over most of crown simultaneously
Top leaves become boat-shaped
Formation of witches'-brooms in some elm species (dense shoot clusters)
Loss of apical dominance

Potential Damage

Systematic breakdown of phloem tissue
Disruption of nutrient transport
Cambium failure and tissue death
Complete crown defoliation
Tree death within weeks to end of growing season
Loss of normal growth patterns

Lifecycle

Disease symptoms typically become visible between July and September. Phytoplasma causes callose deposition within sieve tubes and subsequent cell collapse. Cambium fails to replace affected phloem as newly produced cells become necrotic.

Professional Treatment Approach

1

No effective treatment available

2

Remove infected trees to prevent spread

3

Control insect vectors if known

4

Maintain tree health to delay symptom development

5

Plant resistant elm species

6

Quarantine infected areas

Recommended Mauget Products

No effective chemical treatment available

Professional-grade treatment specifically effective against elm phloem necrosis (elm yellows).

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