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Lecanium Scale Insects
In Manitoba, where I live, I have observed ever-growing numbers
of lecanium scale insects (Parthenolecanium corni)
feeding heavily on the twigs of ash trees and many other deciduous
trees in the southern part of the province. As the twigs die,
so do their supporting branches. Ultimately, a significant
portion of the crown dies as the population of scales escalates.
Populations are usually higher in boulevard ash and other
deciduous boulevard trees, which bear the brunt of winter
road salts.
Again,
the best means of control is spraying with dormant oil.
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| Green ash twig with lecanium scale insects. |
Ash Leaf Anthracnose Disease
Ash trees have compound leaves, meaning each leaf consists
of a single leaf stalk supporting separate leaflets. Anthracnose
diseases (Gnomoniella fraxini and Discula fraxinea)
in ash trees causes brown blotches in the leaflets and may
cause the leaf stalk and leaflets to prematurely separate
from the twig.
I am now seeing a form of anthracnose disease in twigs, especially
in Mancana ash trees (F. mandshurica 'Mancana') that
have endured repeated anthracnose leaf infections. The disease
appears as a linear swelling in the twig, with the twig bark
splitting into fine parallel cracks.
As the disease intensifies, these lesions or cracks open
up and become spore-producing fungal cankers. The spores will
travel through the air and infect other ashes, including the
originating ash tree.
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