Lee Valley Tools    Gardening Newsletter
   Vol. 4, Issue 4
   August 2009
  Ash Tree Decline

In forestry and arboriculture, decline generally refers to a gradual weakening of tree health as a result of disease, pest or other environmental factors. The tree's defence strategies simply cannot keep up with the adverse growth factors. Ash decline is the result of several causal agents.

Cottony Psyllids
A type of sucking insect, cottony psyllids (Psyllopis discepans) seem to flourish in drought-stressed trees. They suck on the leaves, causing them to curl tightly. Repeated annual occurrences will weaken ash trees' defences and can cause slow or abnormal growth, twig and branch death and, ultimately, tree death. They are more of a problem in the western parts of the Prairies.

The best way to control psyllids is by using insecticidal soaps in spring.

Ash Flower Gall Mites
A common pest typically found on the male flowers of the green ash (Fraxinus pennsylvanica var. subintegerrima) and black ash (F. nigra). Ash flower gall mite (Aceria fraxiniflora) infestation produces an unsightly mass of brownish-black galls or swellings in the dried flowers located on discrete small twig-like growths. With some effort, the galls can be removed on smaller trees; however, they do fall off with time. This pest does not apparently harm trees; instead, it affects the aesthetics of the tree.

The best means of controlling gall mites is to spray the entire tree with dormant oil before the spring buds open.

Tree infested with ash flower gall mites.   Ash flower gall mite infestation close up.
Tree infested with ash flower gall mites.   Ash flower gall mite infestation close-up.
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