Residue around indoor mini rose

[PureBlackVoid]

I have a mini rose and a bougainvillea on a windowsill, amongst other non flowering house plants. Both the rose and bougainvillea have little flies in the soil, but ONLY the rose has some sort of residue around on the glass, and window sill. It looks like something has been sprayed around it.

The texture is like dried spilled juice ( but definitely not spilled juice). I’ve wiped it off 3/4 times, it keeps reappearing and it’s not somewhere a spill could easily reach.

I don’t think it’s the flies because there’s nothing around or close to the bougainvillea. There doesn’t appear to be anything on the plant or pot itself.

Is the rose ‘spraying’ something? Any ideas what it could be?

It’s usually an indication that you have greenfly on the plant. Or possibly scale insect.

The flies will be fungus gnats, emerging from transparent root-eating larvae intge soil.

Thanks. Google seems to suggest the gnats won’t damage the plant, and are caused by overwatering. I do water these two more frequently but only because they dry out so quickly. Is it worth replacing the soil?

Definitely change the soil if there's overwatering an gnats. Firstly, the dampness can start to smell. Sometimes the topsoil can dry out but underneath is still wet.

Also, don't underestimate how annoying fungus gnats are. I've now been living with them for 9 months...

Water from below and put grit on top of the soil.
Use sticky papers, about a fiver from Amazon, to trap the gnats and stop the breeding cycle.

Google is wrong. The gnat larvae won’t damage fibrous roots, and probably won’t hurt the rose, but they do damage thick fleshy roots and can kill a plant