Our house was sided this spring. The windows were framed in aluminum. As illustrated in the picture attached, it looks like we're getting some type of corrosion around the window sill. --almost like what you see on the post of a car battery. At first, I thought it was plant life, some type of fungus like you find around the base of trees. But I don't think that's it. It's on all the windows: some alot, some only a little. Does anyone have any idea what this might be or how to fix the problem? The job was completed 5 months ago.

Is that the exterior?

This substance is only at the base of the windows, right? It almost looks as if it's being squeezed up over the top of the siding, but I don't have any idea what it would be unless some kind of spray foam might have been used, or something else was applied underneath the top of the siding at the base of the window, or beneath the window.

I hope others can identify it for you. It must be disconcerting.

Was this coil stock installed over pressure treated wood?

Thanks to everyone who replied to my inquiry. I figured out the problem. The windows were framed with plywood. An aluminum facing was fixed over the plywood. Somehow, the plywood "swelled-out" or otherwise protruded so that some of the plywood was exposed. Fungus then grew on the wood. So, the fungus (shown in my photos) is the symptom of the larger problem, the exposed plywood. Doesn't look like an easy fix.

Did they just install that coil stock flat without bending it at the top so it slide under the bottom of the window?
A big no no if they did.

More pics, better angle.
::Tail wag::
Ty