Black Knot

I received more than one comment or email on my Foam in the Creeks post which armed readers with information that could make them nature Smarty Pants when hiking with friends…

Well, here’s another one that may help you when someone asks, “What is that black stuff on the branches of that tree?”

Img_00

The black, warty galls appear on trees in the Prunus genus. In this case it is Black Cherry (Prunus serotina), but it often affects wild and cultivated prune and plum trees as well.  Because all these trees have commercial value, you can find plenty of information about Black Knot (Apiosporina morbosa) and how to control it online!

The Cornell site listed below includes this diagram explaining the “disease cycle” of Black Knot:

While there are fungicidal treatments that can be used, most of the articles first recommend pruning in winter and removal from the site and/or burning of the galls.

Img_01Michael Kuo, author of many of the articles at MushroomExpert.com, has a great sense of humor.  First, he describes Black Knot as looking like “dried cat poop on a stick.”  Each article at the Mushroom Expert site includes information about whether or not the species is edible.  Regarding Black Knot, he had this to say:

As far as the edibility of Apiosporina morbosa is concerned, I have four words for you: Look at the picture.

He cracks me up.

Sources:

Mysteries in the Woods – Part III

I don’t know how long it’s been there.  I just noticed it a few days ago while walking the dog in the woods behind Bergman Park.  It kept catching my eye throughout the walk – so it was fairly widespread.  When I found one last example on my way back to the car, I decided I just HAD to stop for photos.

Mysterious Stuff on Brambles   Mysterious Stuff on Brambles

Strange, fuzzy growths on the stems of brambles – I’m not sure what kind of brambles.  Whenever I see strange growths on plants that seem to be made of plant material, I think galls…  I really don’t know for sure about these, though…  These plants also sometimes have a wad of wilted leaves up at the end of the stem:  I’ve read those ARE caused by an insect.  But some plants have just this, others just the wilty leaves.  It may have been a coincidence that some plants had both, just like you can find both ball and bunch galls on a single goldenrod plant.

So… any guesses from my nature nerd readers?  (And I call you “nature nerds” with the greatest of affection!)

Insect Galls

Downy Woodpecker snacked hereImagine being able to release a chemical that makes a house grow around you.   There are critters that can do this.  Insects, mostly.  In winter, when the foliage has fallen away from the plants, you can find plenty of evidence.  The “houses” they create are called a galls.

It seems the larvae of gall-producing insects release powerful growth hormones that cause plants to grow in unsual ways… creating perfect shelters for themselves.  Each gall-producing species has a preferred host, so when you find the “house” you can also know the insect that produced it.

The Goldenrod Ball Gall is produced by a fly larva (Eurosta solidaginis).  Read more about it by clicking here.  I also wrote about it last March.  You can read that post here.

Chickadee Snacked HereI think the fun thing to notice about Ball Galls in winter is the shape of the hole – if any…  No hole means the larva is still inside.  A pinhole means this is a 2-year-old gall and the adult escaped last spring to lay more eggs.  Larger holes usually mean bird activity; birds know there’s a tasty snack inside!  The picture above shows a gall that was visited by a downy woodpecker.  With that long pointy beak, a downy can get right to business finding the larva inside.

This gall was visited by a chickadee…  Shorter beak and much less precision in finding the snack!

Willow Pine Cone GallThe Willow Pine Cone Gall is another fairly conspicuous gall that you might find on a winter walk in the Great Lakes region.  This one is caused by a tiny midge (Rhabdophaga strobiloides).  The adult lays eggs at the branch tips.  The larva burrows in and the gall is formed right at the end of the twig.  It so resembles a pine cone – the seed forming part of conifers – that many people mistake it for the seed-producing part of this plant.  Nope!  It’s an insect house.

Willow Pine Cone Gall Cross-section

 

 

 

Slap me if you are getting tired of references to Stokes Guide to Nature in Winter.  I can’t help it if it has a lot of interesting stuff in it, like this:

What has attracted attention to this gall, besides its beauty, is the tremendous number of other insects that use it for overwintering and breeding…  For one study 23 galls were collected and 564 insects were reared from them.  Only 15 contained the original host gnat, but in addition there were 6 wasp parasites, 169 other guest gnats, and 384 eggs of the Meadow Grasshopper…

It’s all too fascinating… Nature never ceases to amaze me.

Learn more about this topic:

Taking Things for Granted

Tree with KneesI learned about Trees with Knees from my Girl Scout camp counselor back when I was a very young girl.  We were taking a tour of our tent unit when we found a tree similar to the one pictured here.  “Pickles” explained that a long time ago, a seed landed on an old stump and began to sprout.  Since it had not landed in soil, the roots had to grow over and around the stump to get to the forest floor.  Over time, the “nurse stump” slowly rotted away, leaving the roots in their original positions – looking like the legs (with knees) of a strange, long-necked animal.

The first time I encountered this tree with a group at Audubon, I was surprised to discover they didn’t know what caused the “knees”.  I had lived with this knowledge so long I just assumed everyone knew.  When I gave the explanation and saw how amazed my group was,  I realized that I had lots of that kind of knowledge that I could share… that there were plenty of things I had learned about the natural world over the years that might not be common knowledge… things people might be fascinated to know.

This goldenrod has both a midge gall and a fly gall!Another favorite misconception I love to clear up for people is the nature of that bump in the middle of some goldenrod stems.  I’ve heard people call it a seedpod, or a disease…  The truth is even more fascinating.

There is a fly that lays eggs on the stems of  goldenrod in the summer.  When a larva hatches, it bores its way into the center of the stem to find everything it needs to survive:  food, water, and shelter.  The plant responds to the activities of the larva by growing extra thick layers of tissue in the shape of a ball around it.

The fly emerged...When fall comes, the larva creates an exit hole – right up to, but not breaking through the outer skin of the gall, then returns to the center to spend the winter.  In spring, the larva will pupate and eventually use the exit hole to emerge as an adult.  If you find a gall with a smooth small hole, the adult has emerged.

A downy woodpecker had lunch here.Sometimes the fly is not so lucky.  There are too many creatures out there that know about this secret life.  Birds, such as chickadees or downy woodpeckers, may peck holes into the gall to find a tasty lunch.

And, of course, there is the overzealous naturalist who finds a gall with no hole at all and wants to show her charges the contents.  (Who me?)

Fly larva in center of gall...Would you believe there’s more?  For example, there are wasps that drill into galls to lay eggs so that the wasp larva can feed on the fly larva.  It’s all too fascinating… and I never tire of teaching people about it!  (While hiking with the Cub Scouts, we also found oak leaf galls and willow galls.)

P.S.  After showing my Cub Scout group the gall, we happened on this water snake – the first I’ve seen in 2007.  After I explained that while water snakes are not poisonous, I don’t like to pick them up, since their saliva has an anti-coagulant that keeps your blood flowing after they bite you, which they almost always do… one young Cub Scout decided he wanted to try picking it up anyway.  Water SnakeHis first attempt made the creature turn it’s head toward the boy, then slither a little way down the bank.  That movement was enough to convince the dad that his son was not going to get a second chance.