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Table: Diagnosis and Control of Ash Yellows
Pest Identification Host Plants Damage Symptoms
Ash Yellow,
Phytoplasma (Mycoplasma Like Organisms, MLO's)
White, red and green ash trees, with white ash sustaining the greatest damage. Ash yellows disrupts the physiological function of the tree by reproducing in the phloem. Infected trees show a 50% reduction in growth, witches brooming, deliquescent branching (loss of dominance), and sprouting out of the main trunk. Susceptible trees may die in 1 to 3 years, while resistant trees may live for several years.
Monitoring Control Options Pesticides
Ash yellows is visible in infected trees one year after infection. Ash trees should be monitored for visual symptoms of such as witches' brooms, deliquescent branching, etc. There are no known control methods for ash yellows. Avoid grafting with infected trees. Increasing the vigor of the tree may help to prolong the life of the tree. None
Description and Life History
Description: Ash yellows is a systemic infection caused by a phytoplasma (MLO). This disease infects the phloem and causes decline of the ash tree. This disease is thought to be vectored by insects such as leafhoppers or spittlebugs. Diagnostics of the pathogen can only be done with visual symptoms or a Scanning Electron Microscope.

Life history: Ash yellows appears to be vectored by insects. Once the insects have distributed the pathogen into the tree, the pathogen begins to reproduce in the phloem. This stresses the tree causing the tree to have a reduction in growth (50%). The pathogen then is transmitted from infected trees to healthy trees. It also appears that the disease can be transmitted through grafting.

Overwintering: The pathogen is thought to overwinter in infected wood.


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Last modified on March 07, 2013