Tuesday, 7 December 2021

How to: not scream in fear at Mossy Rose Galls

 “A Rose by any other name would smell as sweet...” 

...said the Bard, but would it smell quite as sweet if you pushed your nose into one of these Mossy Rose Galls, I wonder? 


Weird, isn't it? Also known as a Robin's Pincushion gall, which is sweet, or rose bedeguar gall, which is unpronounceable: but I think that Mossy Rose Gall sums them up more neatly.

I occasionally come across odd mutations in the garden - fasciation is the usual one -  but yesterday I found this fluffy-looking gall on a hybrid tea rose. 

It's quite common to find them on Dog Rose, less common to find them on cultivated garden roses, but always interesting....

Like most galls, the Mossy Rose gall is formed by the action of a wasp, which lays eggs in a bud, or a developing leaf, during the summer. In this case, it's a particular Gall Wasp, with the lovely name of Diplolepsis rosae. Sounds more like a dinosaur with a sleep disorder, but no, it's a teeny tiny wasp. 

The eggs hatch into tiny maggots, which secrete a potent cocktail of chemicals, and it's these chemicals which cause the rose tissue to grow in this strange, distorted formation. 

Most of it is for protection: against the weather, and against predators and parasites. 

That outside layer might look fluffy - right -  but it's actually quite hard to the touch: not prickly, but rather like a brillo pad made of wood.  

Inside the gall is a series of small chambers: and by autumn, these would be filled with fat maggots, about to undergo their second major transformation. 

By the following spring or summer, the gall will start to rot and disintegrate, and the new generation of adults will emerge.

Here's a photo of a couple of large ones which I found while out walking one day:

Note that I am wearing gloves to handle them!

Do they hurt the plant? Well, no, not really: they do rob the plant of nutrients - proteins and carbohydrates - which the maggots use as they develop, but most roses won't even notice the difference, and it certainly won't kill a plant.

However, if you find them unsightly, just prune out any affected branches and burn them: this also destroys the developing wasps, so you're slightly reducing their population for next year.

And if you have a massive infestation of them one year, you could always cut them out on long stems, dry them, spray them silver and use them for Christmas decorations.

 So it's not a mad mutation, or some horrible infectious disease which is going to ruin your roses: it's a simple "nest" in effect, for a particular small wasp.

No need to scream in fear, if you find any! 



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