Something always spoils the applesauce, doesn't it? You're anticipating a good rose year, checking the roses daily and closely to catch a glimpse of that first bud on a new cultivar in your garden. And then you see that first leaf affected with blackspot. Or the fine new rose cane broken off at the base by recent winds. Or the cute little spiky balls hanging on one of your roses.
Cute little spiky balls? Wait a minute, I think those are rose galls!
I've seen similar structures on oak trees, but never on my roses. A quick bit of Internet research tells me that my assumption is probably correct. These galls are likely formed by a gall wasp, perhaps a Diplolepis sp. wasp, who lay eggs on the roses in spring and whose larvae then become encapsulated within a chemically-induced distortion of the plant material. Cut a gall ball open, as I did, and you are met with a moist cavity containing a very squirmy, disgusting, tiny white larva who is quite perturbed at the disturbance. After a more careful search, I did find some smooth balls on another rose ('Banshee') which contain similar larvae, but that seems to be the extent of my infestation. As I am not an entomologist, I'm at a loss to determine exactly which species has chosen my rose (in this case 'Marianne') to invade, but it is probably not the Rose bedeguar gall, Diplolepis rosae, as it isn't "mossy" enough in appearance. One source, a University of California Extension publication by ML Flint and JF Karlik, suggests that there are perhaps 40 different types of rose gall. Even worse, according to Wikipedia, there are some 800 species of gall wasps in North America.
For the life of me, I can't find a decent "reason" for the existence of gall wasps. Okay, they form galls, but what else do they do? Don't laugh, it's an important question. I need to know if I should crush these galls under my heel or let them mature on the contingency that gall wasps are a beneficial predator of a far worse disease agent. A rose blooms to please the rosarian and its pollinator and make new little rose seeds. An oak tree forms acorns to make little oak trees and provide squirrels an incentive to plant the acorns. Is being a plant parasite the sole purpose of a gall wasp? To make more galls and thus more little gall wasps?
I may be waxing a little too metaphysical today. If I carry my thought a little further, I must also acknowledge that the gall wasp may be by turn wondering what my existence means. Does the large bipedal mammal exist solely to protect his roses and make more little bipedal mammals? Or merely to write about his fleeting thoughts and send them out into the ether? Exactly how many angels can dance on a rose bud?