Willow trees are members of the Salicaceae family, with popular species being the weeping willow and corkscrew willow. These trees are often used as specimen trees in residential and commercial landscape designs. While willow trees are generally healthy, they are susceptible to rust, which can cause the leaves of the tree to turn yellow.
Rust is a disease that often affects willow trees and is caused by the fungus Melampsora medusae. This disease is spread by fungal spores that overwinter on fallen plant debris. Spores are carried through water or on the wind to infect other trees. Rust spores can infect trees up to several miles away. Rust is most severe during periods of wet weather.
Rust causes leaves of infected willow trees to turn yellow, especially at the lower leaf edges. Yellowing usually begins as leaf spots, which enlarge over time to cover more of the leaf surface. As time goes on, infected willow leaves develop an orange or brown crusty coating which holds the fungal spores. If rust is severe, it can cause willow trees to lose their leaves prematurely and suffer from severe defoliation.
Since rust spreads through fungal spores on dead leaves, it is important to rake up and destroy all infected leaves after they have fallen. Do not use infected leaves for mulch or compost, to avoid spreading the fungus to other trees. Rust is most damaging to newly transplanted willows or very young seedlings.
Cultural control methods can help reduce rust infections, but chemical controls may be necessary to protect high-value trees from infection. Spraying your willow trees with a protective fungicide may help prevent rust from damaging your tree. Apply fungicides to your trees every seven to 10 days to prevent rust from infecting your tree and continue throughout the growing season.
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