It's the kind of backyard discovery that can stop you dead in your tracks: The presence of mildew and algae on your wooden fence. In all likelihood, this section of your fence got wet, stayed wet and was shaded from the sun -- three conditions that allowed the mildew and algae to grow. But now's the time to take the upper hand. If you don't have a pressure washer, you'll want to rent one. It's the best and most efficient way to eradicate the problem.
Clear a wide path around the section of fence you will be working on. Set breakable objects and container plants out of the vicinity.
Remove dirt, cobwebs and other surface debris from the fence with a hose or the pressure washer. Attach the proper tip to the pressure washer; it might require different tips for water only and water mixed with detergent.
Add a quarter-cup of liquid laundry detergent -- it will dissolve faster -- and a quarter-cup of bleach for every gallon of water in the power washer bucket, sometimes referred to as the reservoir.
Test the solution -- and your technique -- on an inconspicuous section of the fence. Standing at a distance of about 2 feet from the fence, hold the nozzle of the pressure washer at a 45 degree to the fence. This will allow the mildew and algae to simply slide down the fence, away from you. Move the nozzle in a constant side-to-side motion.
Rinse the fence with water only, either with the pressure washer or a hose. If stubborn spots of mildew or algae linger, repeat the process on those problem areas, but wait for the fence to dry first.