Isn’t it a funny thing? The more you know, the more you see. Before I knew much about galls, I never saw any. Once I started to learn a bit about them, however, they suddenly seemed to be everywhere! For example, when I was driving down a rural road last weekend, I noticed this tree with suspicious blobs on the lower branches. I stopped the car and took a closer look. At first, I thought they must be some sort of seed cone, but no, they’re galls. Ash flower galls, to be exact.
The galls are caused by mites (Eriophyes fraxiniflora), who attack male flowers during blossom development in the spring. The mites feed in the flower clusters, causing them to become irregular masses. Female mites then lay eggs in the developing galls. The galls are green early in the season, but gradually turn brown or black. The galls can remain on the tree for as long as a couple of years. The tiny mites can develop from egg to adult in under two weeks and many generations can occur over the growing season. Females overwinter under bud scales or bark. The galls do not harm the tree and the galls add visual interest in the winter. However, most ash trees are dioecious – a single tree will contain only male (staminate) flowers or female (pistillate) flowers. As the mites attack only male flowers, gardeners who don’t like the galls can avoid them by planting only female trees.
Willow House Chronicles 
Fascinating. I would have never thought that these dried up flower looking things were galls. I will check out my ash trees to see if they are male or female. Thanks — barbara
That’s neat! It’s almost like a party trick, driving down an unfamiliar road with someone, and casually pointing out the window to say, “Look, a male Ash tree!” You’ll have to turn off CBC Radio 1 for all the conversation that ensues.
“And isn’t it a funny thing …”. Can you write and/or say that without thinking of Vince? I can picture him, and hear his voice, clearly whenever I see/hear it.
Barbara, they do look just like dried up little flowers. Pretty neat.
LB, What, turn off CBC…
Grammarian, no, I cannot. Not sure why that phrase sticks so tightly.
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How do you know if your ash tree is diseased?