I would use something like jomax siding cleaner and a pressure washer light stroke.
How to remove fly specks from vinyl siding.
Wet a paper towel with the solution.
Combine equal amounts of white vinegar and water in a bowl or spray bottle.
Peroxide hydrogen peroxide has also been said to work especially at higher strengths.
Use big pieces of pine bark or other bark mulch which are a less hospitable place for the fungus.
Vinyl siding is very popular due to its durability and simple maintenance.
Add a fresh layer of mulch.
Though you may be stuck with a few black speckles for a while here s how you can keep the fungus from shooting any more spores at your house.
If using a bowl wring out the paper towel so it s not dripping.
Test the solution on a small hidden area of the surface first if needed to be sure it is safe such as for a painted wall.
Insect stains and other debris can be removed by simply cleaning vinyl siding with household cleaners.
Apply the jomax with a pump up sprayer let is set a minute then pressure wash or brush it in and use a hose to rinse it down.
This will buy you a year before the fungus reaches to the top of the new mulch.
Remove insect stains from vinyl siding with simple cleaners.
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Dirt and insect secretion stains however can adhere to vinyl siding attracting molds mildews and algae.