Witches Broom - Another Hackberry Gall

Witches Broom on Common Hackberry

This time of year, before the trees leaf-out, it's relatively easy to spot odd growths on trees.   I was driving on Badland Road near Rieck's Lake Park in Alma, Wisconsin today looking at cranes and waterfowl when I spotted this fist-sized knot of twig growth.  At first I thought it might be an abandoned bird nest.

I stopped and got out of the car to get a closer look.  That's when I realized the tree, a Common Hackberry, supported more than a dozen of these strange growths.  That would be way too many nests for one just tree.

Witches Broom on Hackberry

Turns out it's a gall known as witches broom.

Scientists haven't figured out exactly what causes this gall, but they know it occurs when the bud on a tree branch is injured (by winter road salt, a fungus or a bacteria) - or infected by a microscopic mite Eriopes celtis and by a powdery mildew fungus Podosphaera pytoptophila. 

While scientists don't understand how the mite and fungus interact, they do know that it doesn't "kill" the tree.

Witches broom galls are not unique to hackberries.  They can also be found on oak, cherry, birch, red cedar, alder and spruce.

Mites are not the only animals associated with witches brooms.  In Alaska, Flying Squirrels have been known to create winter hibernating capsules in spruce witches broom.  They chew out cavities of the gall and insulate them with a lining of mosses and feathers, making their winter hide-away snug as a bug in a rug.

Robins and Hackberries

American Robins eating hackberries

It was about this time last year that I "discovered" Hackberry trees along the Lower Chippewa River.  They've always been there.  I just never noticed them.

What made me stop and look?  A flock of birds, perched in the leaf-less canopy, silhouetted against a mean gray sky.   Their movements caught my eye.

It didn't take much to identify the birds.  They were gluttonously feasting on a dark fruit the size of cherries.  Had to be Cedar Waxwings or American Robins.  A quick look through binoculars confirmed it:  Cedar Waxwings.

But what were those fruits?  And what was that tree?

I was clueless.  And I felt stupid.  Why didn't I "know" that tree?

Figuring it out required getting out of the Prius (brr) with my little Canon Powershot to get some reference pictures. 

Hackberry Bark

Lucky for me, I could get close enough to photograph the bark.  From there it was easy.  Common Hackberries are known for their "cork-like bark with wart-like protuberances."

Turns out, figuring out the identity of this one tree last fall opened my eyes to some of the other creatures related to it, animals I also spotted for the first time, this past year.

Hackberry Gall Psyllid

Hackberry Emperor butterfly

Hackberry Nipple Galls

Hackberry Petiole Gall (summer)

Hackberry Petiole Gall (winter)

Now that I can identify a Common Hackberry tree, I keep looking for "new" creatures associated with it.

Today it was the same fruits, same tree, same weather - but different birds.  Today's birds were American Robins.

Hackberry Galls Revisited

July's hot and humid weather has created the perfect storm for mosquitos.  They're everywhere.  Bzzt.

They're most active at dawn and dusk, so I've modified my schedule.  I head outdoors around mid-day.  It's not the best time to watch wildlife - so I've modified my viewing targets: plants.

Today's plan:  find and photograph galls - what happens to plants when they're "bitten" by insects.

Hackberry Nipple Galls

Galls are distinctive growths in plants caused by parasites (insects, mites, bacteria and fungi).  The parasites actually take control of the growth of plant tissues.

Hackberry Nipple Galls are formed by jumping plant lice (psyllids).  These insects overwinter as adults and mate in the spring.  I first noticed the adults this spring, when one landed on my arm.  (They're harmless).

Females lay eggs on the underside of Hackberry leaves.  When the eggs hatch, the nymphs, feeding on the leaves, cause the leaf tissue to grow galls around them.   The nymphs feed on these tissues through out the summer and then emerge as adults in September.

 Hackberry Nipple Galls in November

I first noticed these galls last November when the Hackberry leaves littered the Chippewa River Trail.
Crunch, crunch.

 Hackberry Nipple Galls in July

The Hackberry leaves I saw today were literally weighted down with these galls.  But they don't harm the tree.   Amazing how that works. 

Hackberry Nipple Galls and a Hackberry Petiole Gall

I spotted another gall associated with Hackberries:  Hackberry Petiole Galls.  Much larger than the Nipple Galls, they're also created by a psyllid.   Petiole galls are multi-chambered with up to a dozen or more nymphs inside.  The psyllids overwinter in these galls as nymphs and emerge as adults in the spring, leaving behind an empty woody husk.

Hackberry Petiole Gall in the winter

Petiole galls are easy to spot during the winter, providing a quick clue for identifying Hackberry trees when their leaves have dropped.

Hackberry Petiole Gall Psyllid

Pachypsylla venusta (Osten Sacken)

March 15th was one of those unseasonably warm days.  A tiny insect that looked like a cicada (above) was one of hundreds swarming the Chippewa River State Trail.  I didn't get a good look until one landed on my thumb.  It looked like it could suck the guts out of me.  (It didn't).

I had no idea what it might be until today, when I took a photo of this hackberry sapling full of dried galls.  I wanted to see what the insect that made it looks like.  That's how I discovered the identity of my March 15 mystery creature:  the hackberry petiole gall psyllid (also known as jumping plant lice - they suck sap from leaves and stems).   This psyllid species forms woody galls on leaf petioles. 

Infested leaves do not fall from the trees and heavily infested trees are recognizable during the winter by the presence of the dead leaves. The adults emerge in the spring after the nymph cuta its way out of the woody gall.   While they apparently do not harm the hackberry trees, these old galls can remain on the trees for years.

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.