Wednesday, July 8, 2009

Cicada Damage

Last year, the Seventeen Year Cicadas emerged at Blue Jay Barrens. I enjoy the couple months of cicada activity. My only concern is the damage that occurs to some of the oaks growing in the open prairies. These trees are cicada magnets and seem to receive an unfair percentage of cicada egg laying attention. Trees are showing a lot of brown where cicadas killed the branches. The female cicada splits the young tree branches and lays eggs within. This causes the branch to dry out and die. The weight of the leaves on the branch causes it to break and hang down in a display known as flagging.

Most of the oaks found in this part of the prairie are Blackjack Oak, Quercus marilandica, the host plant of the Edwards’ Hairstreak Butterfly. No need to tell me I’ve mentioned this fact before. I’m aware that I sometimes repeat things many times. But I do become concerned about the oaks, because damage to the oaks can mean damage to the butterfly population and I like those butterflies. Seventeen years ago the damage was much more extensive and the Edwards’ Hairstreak population was greatly reduced. It took several years for the butterfly numbers to recover.

Most of the oaks are small and can suffer considerable damage.

Here’s typical damage done to the small twigs. This type of damage usually causes the branch to die right away.

This is damage done to the main trunk. The trunk was thick enough to survive the initial damage and is healing nicely. Although this type of damage doesn’t kill the branch immediately, it causes structural damage that will most likely cause the trunk to break at this point several years from now.

Small trees are favored for feeding by the Edwards’ larvae. Maybe the cicadas actually keep the trees at a small size to the advantage of the butterflies. It doesn’t really matter. All I can do is observe and hope everything works out all right.

This young lad has lost over half his top growth. You can see the reddish colored new growth beginning near the ground.

This tree is left with almost no leaves. Some leaf loss is the result of cicada damage. Most of the leaves that did grow this year were eaten. You can see just a few places where the tree is any leaf growth. Cicada damage and defoliation combined with shallow soil and dry conditions may mean the end to this tree.

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