DiseaseHigh Severity

Elm Phloem Necrosis (Elm Yellows)

Phytoplasma sp.

A fatal systemic disease of elm trees caused by a phytoplasma organism, formerly known as elm phloem necrosis in the U.S. and witches' broom in Europe. The pathogen destroys phloem tissue, disrupting nutrient transport and causing rapid tree death.

Peak Season: Symptoms typically appear July through September. Late summer or autumn infections difficult to distinguish from normal senescence. Spring symptoms appear on late-season infected trees.
Phloem necrosis showing characteristic yellowing and crown dieback

Identification & Symptoms

What to Look For

Leaves droop, curl, and turn bright yellow then brown
Premature defoliation occurring over most of crown simultaneously
Top leaves develop characteristic boat-shaped appearance
Inner phloem and outer wood turn lemon-yellow to butterscotch brown
Discolored tissue emits faint odor of oil of wintergreen
Witches' broom formation in some elm species (dense shoot clusters)
Loss of apical dominance with multiple terminal shoots

Potential Damage

Rapid tree death within weeks to one growing season
Systemic phloem destruction throughout tree
Cambium failure to replace affected phloem tissue
Complete disruption of nutrient transport system
Trees infected late in season show thin twigs and small leaves the following spring
Economic losses in urban and forest elm populations

Lifecycle

Signs typically become visible between July and September. Infection begins with rootlet necrosis followed by degeneration of phloem and cambium in roots and lower trunk. Late season infections may not show symptoms until the following spring.

Professional Treatment Approach

1

Remove and destroy infected trees immediately to prevent spread

2

Professional diagnosis essential due to similarity to Dutch Elm Disease

3

No effective cure once symptoms develop

4

Apply preventive treatments like Arborfos to maintain tree vigor

5

Monitor for characteristic wintergreen odor in phloem tissue

6

Vector control may help reduce transmission in some cases

Recommended Mauget Products

Arborfos

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

View Product Details

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