Ornamental plants are used to add visual interest to a landscape, such as woody shrubs, flowering trees and colorful annuals. These attractive plants can add as much as 15 percent to the value of a home, according to Mississippi State University. For that reason, diseases of ornamental landscape plants are not just bothersome, but costly. Luckily, many of these diseases can be prevented with good cultural practices.
Botrytis blight is a fungal disease that affects a large range of ornamental plants, from perennials and vegetables to bedding plants. These fungi spread on water (usually rain). Botrytis blight can infect any part of the plant except the roots, according to Cornell University, but it often affects newly developing plant tissue first. New flower buds and developing fruit will appear covered with a fine, brown or gray fuzz. In fact, the disease is also frequently called "gray mold." Botrytis blight renders fruits and vegetables inedible and it disfigures ornamental plants, often preventing flower buds from opening, or causing them to become discolored or disfigured.
Keep plants from becoming overcrowded. Make sure plenty of air can circulate around the plants and locate ornamental plants where they will receive morning sunlight, which will quickly dry moisture on leaves and reduce the chances of the fungus from developing. Promptly remove any part of the plant that has a moldy covering or looks like it is rotting. This can stop the spread of the disease. Fungicidal spray can help protect ornamental plants if it is applied early in the spring, before cool, wet weather arrives.
Nematodes are tiny, round worms that live almost anywhere. Many live in the soil, where they enjoy a symbiotic relationship with plants. Others are parasitical, and of these, it is the root-knot nematode that is most harmful to ornamental plants, according to the University of Arizona. These microscopic pests can infect a wide range of plants, including fruit, vegetables, shrubs and even trees. The disease affects the roots of the plant, causing them to swell up and develop knots. These knots block the flow of nutrients from the soil to the plant.
Plants affected with this disease will wilt, fail to thrive, may become stunted or deformed in growth and will eventually die from malnutrition. The eggs of these nematodes can live for months, even years, in soil. The best way to prevent this disease is to make sure the planting site does not contain nematodes. This can be done by taking a soil sample and having it analyzed. Once root-knot nematodes start feeding on the roots of a plant, there is no way to prevent the spread of the disease.
Root rot is caused by a great number of different fungi, all of which thrive in soil that is consistently soggy. Over-watering or poorly draining soil are the main causes of this disease, which attacks the roots of the ornamental plant, causing them to rot away. The best way to prevent root rot is to make sure the soil is well-draining. Never plant an ornamental plant in a depression in the landscape where standing water collects. Amend heavy, waterlogged soil with sand and peat moss to aid in drainage. Or, plant your ornamental shrubs in a raised bed. Finally, never over-water a plant. If the water is not seeping into the ground quickly, then the plant has probably had enough water.