You can easily avoid it.
Remove fungus from gutters.
Using a power washer clean your gutters to get the initial mildew and grime off.
When decomposing debris is left in the gutters it can clog downspouts and cause water to.
Wet the gutter with a garden hose after pre wetting the area.
Spray it on there let it sit for 15 or 20 minutes and then you can use the pressure washer to blast off the residual.
It s always a good idea to test an inconspicuous area of gutters to see how they will react to the degreaser.
Finally wipe the surface to remove mold spores.
Allow it to stay on the surface for 10 minutes until hydrogen peroxide kills the mold then wipe the surface to remove the mold and any stains it leaves.
Rinse with water and if necessary reapply the chemical to remaining stains and brush again.
Oh and it will totally come off.
So you need to use a house wash like jomax or a bleach and water solution.
I personally use jomax that i buy at lowes.
My husband tried a new miracle cleaner last year and it did nothing.
If that s not possible bleach and bleach based products are the only way to kill mildew and mold.
You can also spray the gutter and then brush it but make sure the rag is damp first to avoid abrasive friction.
You need to treat it first.
If you haven t cleaned the debris out of your gutter yet do this first with a garden trowel.
On stubborn streaks let the chemical dwell longer being careful not to let it dry.
If you have a power washer try that first.
Here is a quick instructional video on how to remove that mold mildew buildup you get on your siding and gutters.
Gutters collect decaying leaves and small twigs making them natural breeding grounds for mold and mildew.
As we said leaving the mold in your gutter may lead to more gutter repair.
Don t know if it s the same one recommended in previous responses.
Apply the properly formulated degreaser to the pole brush mop or rag that you ll be using.