Mossy Rose Galls
There are a lot of wild roses growing alongside of our road at the end closer to town. And all year, I’ve been noticing these odd fluffy growths on them. So yesterday (November 2, 2024), I clipped one off and brought it home.
It turns out that this isn’t what it looks like (some sort of parasitic plant using the rose as a host). It is actually a gall that is part of the rosebush itself.
Galls are basically what happens when a plant gets a tumor. But, these normally occur as a result of an infestation by some parasitic insect. So Sam and I cut it open to see if there was anything distinctive inside.
And the answer is yes, it was full of little white grubs, about half the size of a grain of uncooked rice.
Looking at them a bit more closely, it looks like they are basically pupae at this point. Wiggly, but with no obvious mouth.
So anyway, these are pretty obviously Mossy Rose Galls, which are caused by the parasitic wasp Diplolepis_rosae. These are mostly parthenogenic wasps (the vast majority of them are females), and they lay their eggs in leaf buds of rosebushes in early to mid summer. They obviously lay a large number of eggs in each bud. The larvae secrete some chemical that makes the bud grow in all funny, turning into this fluffy mosslike mass instead of the compound leaf it was supposed to make. The larvae then hang out inside the gall, feeding on plant juices in the relative safety of their little wooden cells. In October, when the rosebush starts shedding its leaves, the larvae start gradually turning into pupae, which takes until about February. The pupae then finish out the winter, and emerge from the now dried-out gall sometime after May to go lay eggs on some more rosebushes.
If you search on these online there are a lot of sites that talk about how to get rid of them. But, there is general agreement that they don’t seem to cause any actual harm to the plants, and any “damage” they may cause is purely cosmetic. I personally think they are pretty amusing, and so would probably not even try to get rid of them. But that’s just me.