Alittle bit of bleach & some warm water should do the trick
But won't bleach damage the colors on the cushions? The cushions are striped.
Hydrogen peroxide kills mold,just spray it on,but color test in a safe spot first.
Dish soap and a soft brush then hangover fence spray rinse with garden hose and let the sun brighten them.
Mix 1 part Dawn dish soap, 1 part peroxide and 2 parts water. Pour in spray bottle and spray cushions. Let set about 5 min. the use sprayer on hose and spray until any sign of suds are gone. Clean cushions at least once a month with this solution.
Vinegar. It cleans, sanitizes, & eats mold for breakfast.
I have never known vinegar to mess with the colors of fabrics and/or outdoor cushions.
spray it on, leave it sit for about 10 minutes, then hose it off to rinse.
sometimes you may have to scrub a wee bit, but in my experience, that is rare.