Ash (Fraxinus spp.)

Posted by shane - December 20, 2010 - A-Z Plant Maintenance, Trees - No Comments

Green Ash – Fraxinus pennsylvanica

Black Ash – Fraxinus nigra

Manchurian Ash – Fraxinus x. mandshurica

Green ash in Mountview neighbourhood in Red Deer.  R. LePage photo.

Green ash in Mountview neighbourhood in Red Deer. R. LePage photo.

I prune the various ashes in the same manner.  All are relatively slow growing.  Black and Manchurian ashes are prone to cottony ash psyllid, a devastating insect problem that is difficult to control.   Currently, I am injecting two restricted chemicals into the trunks of infested trees: Confidor (17% imidacloprid), and Acecap 97 (acephate).  I am having success with both chemicals.  The City of Red Deer used acephate in their control regimen for city trees with excellent success.  While seasonally effective, both systemic chemicals require an injection, and therefore an injury, to the trunk tissue.  Also, systemics must be used each year to control the disease.  We may be fighting a losing battle with our black and Manchurian ash trees.  I no longer recommend the planting of either species.

Some of my clients, who prefer to control pests on their own, are having success with insecticidal soap, applied every 10 days from bud break, throughout the summer.  The insects have two life cycles, the first beginning in late May to early June, and the second in early August.  Trees sprayed every 10 days were virtually unaffected.

I also found that the during the wet spring and early summer of 2010, insect populations were very low, thus allowing infested trees to survive another year.

Pruning Time: Dormancy (preferred); 10% of canopy (anytime); ideal time is late winter to early spring.  Avoid pruning during bud break up until the leaves are expanded.

Structure: train as central leader standard with well spaces scaffold branches along the trunk.  As green ash are usually used for boulevard trees, it is normally useful to start the main scaffold branches above head height.  On mature trees, with codominant leaders and included bark in the crotches, subordinate the smaller of the two leaders.  Older specimens with poor attachments that are likely to split, may have to be cabled and/or braced (see cabling/bracing).

Mature Form:  As with most large, mature trees, I prefer a well balanced overall shape.  It may occasionally be necessary to reduce the width (see width reduction) of the trees using reduction cuts.  This will balance the form and will also reduce end-weight on horizontal branches, which helps reduce the incidence of storm damage.  Clear branches growing into structures and train branches to grow up and over houses.

Crown Reduction: Green ash trees can tolerate crown reduction.  They were once a popular Genus used in pollarding in Europe.

Health: Remove deadwood.  Remove branches that are infested with ash bark borer to slow the spread of the insects.

Irrigation: although drought tolerant, these trees prefer moist, well-drained soil with a mulch cover over the root zone.

(c) Shane LePage, Wild Rose Tree Service 2010, Red Deer, AB