Tuesday, November 3, 2009

Crunch, Crunch: Hackberry Galls

It was the noise that drew my attention to these odd corn-shaped growths on the downed leaves along the side of the Chippewa River State Trail this afternoon.  The crunch, crunch, crunch.  I had to stop to see what the crunch was all about.

There were literally thousands of them attached to the dried up and brown leaves that littered the macadam.  What were they?  Not maple, ash, elm or cottonwood.

I looked around at the naked trees.  Only the oaks were still holding on to their leaves.  Botanists have a word for this:  marcescent (leaves that wither but don't fall off).   Definitely not an oak.  But what?

Then I noticed that tree with the odd bark.  I looked up at the branches, and there it was:  a lone, brown leaf with the dried "corns," spinning in the breeze.   A Hackberry tree.

What was the crunchy corn stuff?

I guessed it was a "gall."  I googled "Hackberry" and "leaf gall."  The internet coughed up several pages of links.   

I went to the "Rutgers - the State University of NJ - Agricultural Extension" web page and there it was:  the Hackberry Nipple Gall, one of 10 types of gall-making insects that attack Hackberry foliage.   

Curious, I went to one of the US Forest Service pages and learned that parasites of the insects that make these galls actually eat the galls after they eat the insects that originally created the galls.  The insects, called "psyllids," look like miniature cicadias (4mm or 1/8 inch).  

They emerge as adults in September, and over-winter in the cracks and crevices of tree bark.  The adults have an interesting nickname:  jumping plant lice.  They're considered a nuisance when they emerge in huge numbers.  (They get on cars, in buildings, etc.)  

I don't have any Hackberries nearby - but I know the feeling, the nuisance, annoyance, etc of  Asian ladybug beetles and box elder bugs.

Most of the Extension experts concur - if the Hackberry in your yard is "infested" with nipple galls, there's no need to spray.  These psyllids may look bad, but they do not damage trees.

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