Black Fly and White Fly:
Both black and white fly spread and grow incredibly quick. Black flies give birth to live young, while white flies lay eggs. Broad leaved plants are most frequently the victim of these pests. Symptoms of black and white fly infestations include yellowing, decaying leaves, as well as frequent sightings of the flies themselves. Be careful when treating these pests, as many available pesticides will be hazardous for fish and other living things within your pond.
Spider Mite:
Damage from spider mites can appear as small yellow or brown spots, or webbing on leaves that looks like it's been left by a spider. Spider mites are too small to spot with the naked eye, but it can often be identified by its webbing. You’ll often find these critters in places where it’s hot and dry. Spider mites are often combatted through employing the services of their natural predators, such as ladybugs. Other solutions involve wiping down the plant itself, including its leaves and infected areas, with a blend of neem oil or another natural insecticide. You may have to repeat this process several times in order to eliminate enough eggs and larvae to prevent the infestation from continuing. Always try to remove any damaged leaves, or places where webs have taken over.
Leaf Spot:
This describes a multitude of diseases that can take hold of plants, resulting in spotting damage on leaves and foliage. This is often a fungal infection, but sometimes can occur due to bacteria. Water lilies seem to be particularly susceptible to the fungal form of this disease. The best solution when you begin observing evidence of leaf spot is to trim and remove the most affected leaves and parts of the plant. Additionally, removing the affected plants from others may prevent the disease from spreading further. Try to prevent getting leaves and foliage wet while you’re watering the plant, wet conditions encourage fungal and bacterial growth.
Crown Rot:
Crown rot is also known as southern blight and is most common in the warmer tropics and subtropics found in the southern US. This is a fungal disease that typically comes from within the soil and is completely lethal once it's allowed to take hold in a host plant. Plants infected with crown rot will yellow and wilt quickly, often within days of first infection. This process speeds up with warmer and more humid weather. ‘Rot’ or water-damage and spotting may appear on the plants ‘crown,’ the part that sticks out of the earth. Mycelia will form between the plant and the soil surface in the form of white, stringy, fungal webs. Crown rot can be spread through the soil itself, in plant debris, contaminated water, or contaminated tools. Remove all plants and soil that appear to be infected with the fungus, throw these in the garbage -- they are no good for composting. Clean and sterilize any tools that contacted the infected material. A complete water change, and thorough cleaning of your pond may also be in order..
Snail Infestations:
Snails are brilliant and hardy little workers in a pond’s ecosystem. They will feed on the waste and organic matter within your water, keeping the pond clean and healthy. However, snails can sometimes become too enthusiastic if conditions are too nice, and their exploding population can quickly become a problem. This is often due to an excess supply of nutrients, meaning there is likely too much food being added to the water. Just like in the case of fish, overfeeding snails can lead to an unwanted population boom, accompanied by its own waste boom. You can thin down excess snail populations by stocking the water with fish that eat snails, or by manually capturing and rehoming the snails yourself. Leaving out a couple of pieces of vegetables is a sure way to encourage snails to come (slowly) running.
Water Lily Beetle:
Like their name suggests, water lily beetles love water lily leaves. They will lay eggs, live, and munch on a singular water lily leaf until there’s nothing left. Thankfully, fish love water lily beetles almost as much as beetles love your water lilies and will gobble up the offenders as soon as they’re swept into the water.