If your spinach has white spots on it, there could be a number of reasons -- and none of them are good. White spots indicate bacteria, fungus or rot, so if your spinach has them, you should throw it away. Though you should always wash your spinach before you eat it, if the spots have already appeared, it’s beyond saving.
Avoid the “Rust”
One particularly common problem affecting spinach is white rust, a fungus. This fungus appears on spinach leaves first on their lower sides, then on their tops. It looks like white blisters on the surface, and though they start small, they grow and consume the leaf. White rust develops in cool, moist environments, like after a rain fall, when water collects on the leaf and makes it hospitable for spores.
Another common blight on spinach plants is cercospora, a fungal disease. Cercospora, which also affects leafy plants like Swiss chard, looks like small white spots across the surface of the leaf -- a single leaf may have a dozen or more spots, or just a few. These tiny spots, which have a dark ring around them, grow and eventually turn gray as the fungus matures.
Steer Clear of Bacteria
A variety of other fungal diseases can cause white spots to form on your spinach, and so can bacteria. Bacterial spots are slightly different in appearance from fungal diseases, but they are just as bad for you to eat -- they mark where bacteria has entered and eaten away at spinach, leaving the plant necrotic and withered. Bacteria spots are identifiable not only by their irregular shape, but by the way the rest of the leaf withers and dies -- the leaf appears frayed and visibly damaged, particularly around the edges, where bacteria frequently enters.
Eating Spinach Safely
You should never eat spinach with white spots, but even if your leaves have no apparent traces of bacteria or fungus, you should wash them before eating. Always wash your hands with warm soap and water before opening a bag of spinach, and thoroughly rinse the spinach leaves in cool, clean water. This washes away not only dirt residue and germs, but also any remnants of the pesticides and fungicides commonly used to prevent white spots from forming.