Browning Leaves on Ash? Likely Ash Anthracnose
A common sight on green ash (Fraxinus pennsylvanica) and
on some Manchurian ash (Fraxinus mandshurica) this time
of year is the browning and twisting of leaves attributed to ash
anthracnose.
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This disease is ash anthracnose (Gnomoniella
fraxini), which is common throughout Canada, on species of
ash grown in cool areas [Mountain Ash (species of Sorbus)
is not a true ash]. While the disease may be unsightly and
appears worse when present with
ash plant bug damage, it is rarely of great concern. Damage
to the tree is usually quite minimal and chemical controls are
often not worth while, with the possible exception of the
production of young nursery plants or the establishment of ash
shelterbelts. |
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Leaf infections result in the formation of large blotches,
and distorted and tan gray areas. Lesions appear in the spring on
expanding shoots and leaves as water-soaked spots. The damage
can be comparable to frost damage in both time that it takes symptoms
to develop and the superficial appearance. Severe infections may
result in defoliation. Extensive defoliation year after year can
lead to dieback on green ash. Distorted leaves develop due to
the stress of healthy expanding tissue near non-expanding dry
lesions. Lesions on expanded leaves are often associated with
insect feeding injuries. |
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This pathogen is restricted to ash trees. It
is not responsible for other anthracnose diseases in beans,
peas, etc. The fungus can survive through winters in
twigs, petioles (leaf stems), leaf veins and seeds. Petioles
infected with the fungus can remain on the leaf throughout
the winter and can be a source of new infections the next
season to nearby susceptible shoots that emerge in the
spring, when splashing rainfalls begin. All succulent plant
tissue can be infected by the pathogen.
The pathogen can
survive on fallen plant material, leaves and twigs, and
could potentially initiate a disease outbreak on the lower
parts of the plant. Thus, removal of fallen leaves can help
to minimize damage and is a recommended management
strategy, especially in nursery production.
Fraxinus pennsylvanica and its cultivars tend to be very susceptible, though varieties do vary in the degree of
susceptibility. Fraxinus manshurica (Manchurian ash) is
considered less susceptible than green ash. |
| Chemical control is not usually worthwhile
but products with the active ingredient mancozeb are
registered for commercial purposes. Recommended cultural
practices include removal of cankered branches and pruning
of trees to allow for good air circulation to speed up
drying of foliage. Promote vigourous growth of the tree
through proper fertilization.
References:
Sinclair, W.A. and Lyon, H.H. Diseases of Trees and Shrubs. 2nd ed.
Ithaca: Cornell University Press.
Author:
Philip
Northover,
Plant Pathologist
Crops Knowledge Centre
Manitoba Agriculture, Food and
Rural Initiatives
Phone: 204-745-5694 |
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For further information, contact your
GO representative.
