Peace lilies don't like a lot of water. They prefer warm and humid environments, but saturating their soil isn't good. If your plant seems unwell, investigate the roots. There are two main forms of root rot in peace lilies. Both stem from either overwatering or inadequate soil drainage. Cylindrocladium root rot is caused by a fungus that can destroy the roots in a few weeks. It shows itself in brown spots on leaves and stalks. Pythium root rot is very similar, but only reveals itself on the leaves. Usually, when you see signs of either, the plant is already near death and the roots are a pulverized goo. If you do manage to catch it early, transplant the flower into a sanitized pot with clean soil containing a fungicide.

Phytophthora parasitica is another type of root rot. However, instead of water, the soil is the culprit. Microorganisms infest the plant's soil and quickly take over. On a grand scale, they can demolish whole ecosystems. For your potted peace lily though, the threat will hopefully be contained. It's best to toss the plant out to reduce the likelihood of cross-contamination.

Peace lilies don't suffer too much from this viral disease, though they do display superficial markings. Dasheen mosaic virus manifests itself on the foliage, and the threat is the flower acting as a carrier of the disease to other plants that don't have the same defenses. Infected pots, gardening tools, or soil are the main way for a peace lily to catch this virus. Insects can transfer it, too. Symptoms show up in the form of a variegating green mosaic pattern on new leaves — older growth is seldom affected. While the disease isn't likely to harm your peace lily, it's best to play it safe and throw it out. There's no cure, so if the virus transfers to another plant, it's likely to be deadly.

There are a lot of plants that don't like water on their leaves, including peace lilies. Leaf blight occurs when water excessively splashes onto foliage. Black or brown dead spots will appear on the leaves, and these patches can be dry or oozing. They'll spread as time goes on, eventually killing your plant. If caught in an early stage, carefully cut off the dead or dying leaves and replant your peace lily in a sterile pot with fresh soil treated with an antifungal agent. Keep in mind that any remaining traces of the blight can morph into a secondary fungus that causes an additional threat.

Too much fertilizer causes marginal leaf burn in peace lilies, which has the potential to ultimately harm roots and kill the plant. Initial symptoms include yellowing leaves that die off. If you detect leaf burn, it's best to transplant your peace lily into fertilizer-free soil. Then be sure to fertilize it only sparingly, on a regular schedule.

Foliar fungus is in the same category as leaf blight. In essence, it stems from splashed water on foliage, but is an intensified disease. Brown circles appear on the leaves, and the undersides display fruiting black blotches outlined in white. Treatment includes spraying the foliage with fungicide and keeping the plant in an area with high air circulation.

Overwatering can breed fungus gnats. Adults aren't really all that harmful to your peace lily, but in the larval stage, they can wreak havoc, feasting on the roots and decaying plant matter. Biological control products, like an anti-gnat treatment, should be added to the soil. This will take care of the larval stage as long as you keep moisture to a minimum and the pot has adequate drainage.

Spider mites are one of the most common insect infestations in plants. Usually they're too small to see, but you'll notice evidence of their destruction. Speckled, faded, yellowing, or bronze leaves are a telltale sign, and in extreme infestations, you'll see webbing on the leaves. Washing the leaves with water will help the situation, but make sure to dry them thoroughly. Insecticides work well too, but the infestation may take several weeks to fully disappear. If you're lucky enough to see the issue only on your peace lily and not your other plants, consider isolating it until the issue is resolved.

Mealybug infestations are hard to get rid of, and they easily spread to other plants. White fuzz on your leaves is a solid indication of their presence. Though small, mealybugs are visible; they have a white and waxy sheen. It's best to be cautious and toss out the infested peace lily so the bugs don't spread to other plants. If you only see a few, you can dab them off with alcohol-soaked cotton, being careful not to touch the leaves. Insecticides are pretty effective as well.