Friday, April 20, 2012

Galls Again

Inky Cap Mushroom
Wednesday we hiked the woods with Maxine Stone in search of all things natural, and hopefully a few things fungal.  We checked the usual vulture eggs, baby bluebirds and lots of wildflowers and found one lonely inky cap mushroom.  Then we came across a small green ash tree with bizarre clusters of green growing on the stem.  Another gall!

Although the gall is on an ash flower rather than a leaf, it is created by an eriophyid mite, the same family that creates the leaf galls discussed a few days agoEriophyes fraxinivorus helps us sex these dioecious trees as it feeds only on the tiny male ash flowers. Ash flower gall mites are too small to be seen without the aid of magnification.

New Ash Flower Gall- click to enlarge
Old gall above new gall

The ash flower gall mite (Eriophyes fraxinivorus) spends the winter hanging out beneath the ash flower buds.  In the spring they mate, begin feeding and eventually lay their eggs on the buds before they bloom.  Less than 1/50 inch, they enter the flower which at this stage appears closed to the unaided eye.

Once inside, their eggs cause the plant to form a totally different structure, the gall that will serve as both a secure home and a kitchen for the larvae as they eat the inner gall contents, develop and grow to adulthood.  After that, they mate, crawl out under the flower buds, and wait for next spring to resume the cycle.

The galls are initially green and hard to see up in a tall tree.  They turn brown late in the season and become more prominent after leaf fall.  Frequently there will be several years of old galls clustered on the branches.

Since ash trees are common in urban neighborhoods, the galls can cause a lot of homeowner concerns but they rarely cause real tree damage.  You can consider them either a pest or another fascinating life cycle in nature.

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