That’s a strange title for a post, you may be thinking. And I agree with you. Obviously all goldenrod updates are important, so the title is redundant.
You may have seen some of my previous posts of pictures from a nearby ditch. They featured pictures of a gall growing midway up an herbaceous plant’s stem. I mentioned that I had no idea what the gall was — the first problem being that I wasn’t sure what the plant was, either. (Plant identification being, of course, the first step in getting anywhere in diagnosing any kind of plant problem, or determining if a problem even exists.)
So I fixed that today by walking back to the ditch, locating a gall, and following a very simple procedure that involved diverting my eyes six inches upwards from the gall. By jove, it was goldenrod. (That’s the problem with my penchant for macros. Not only is the focus in the pictures completely isolated from the larger context, I follow a similarly isolating procedure for finding these pictures by rapidly scanning for tiny details amongst weeds and brush and in little crevices in trees — wherever, really. There’s a bigger picture that I tend not to take in. Later as I’m looking through my pictures I invariably say, hey, what is that, anyway? But I have nothing else to go by than some bark, a swelling, or some other detail.)
Luckily, though, this goldenrod thing was really easy to identify. Almost every plant down there had a gall, and goldenrod flowers are distinct. Using the series of tubes known as the internet, I quickly learned that the gall is caused by the goldenrod gall fly, a parasite that depends on — wait for it — goldenrod for its survival. The fly uses her ovipositor to lay eggs inside the stem of the goldenrod. The larvae feed on the inside of the stem, and something in their saliva causes the goldenrod’s tissues to swell and form the gall. This gall serves as a protective structure for the larvae, who continue to mature inside the plant through the winter. The gall isn’t fail-safe, as some birds and predatory insects know that a tasty treat lurks therein. If they survive, the larvae chew a hole through the gall and emerge in the spring. (More information on the fly and the gall from the Fairfax county public schools website.)
Part of me wanted to go down and cut one of the galls open and look inside, but there are sleeping fly larvae in there. I don’t want to be cruel. I know they’re parasites, but they didn’t ask to be parasites (DID THEY??), and plus, they’ve got a thing going with goldenrod that seems to be working for both of them. Who am I to interrupt it? Any more than I interrupt by stomping all over their backyard, I mean.
Edit: Not positive, but I think the below picture from yesterday might be a gall that was either a) discovered by a predator this winter or b) chewed through in a previous spring by the larvae. You can see some holes throughout it on the top left side.
My googling solved a second mystery I didn’t even know I had. In my past ditch wanderings, I took pictures of what almost looked like a rose with wooden petals. Well, when I went back to the ditch to find the galls, wasn’t I surprised to find one of these rose-like structures also growing on the goldenrod, at the base of the branching that supports the goldenrod’s inflorescence. When I had seen the fake rose earlier, it seemed to be growing independently, the goldenrod inflorescence gone — as it was in almost every picture I’ve seen online of such galls — so I had no idea the plant was actually goldenrod, and didn’t think there was anything weird about the “flower.”
It turns out this formation is caused by the goldenrod gall midge. According to this University of New Hampshire extension website, the midge lays its eggs on the topmost flower bud of goldenrod. Then something funky happens (FUNKY = ACTUAL ENTOMOLOGICAL/HORTICULTURAL TERMINOLOGY) and the subsequent leaf and flower growth form the bunch gall around the eggs. This explains why I didn’t see regular goldenrod flowers growing on the same individual plants as most of these galls.
So those are the things I have learned today. And now a picture before we go.