Trees can get a variety of fungal diseases, which are unattractive and sometimes damaging to the trees. Rust fungus gets its name from its rust-coloured appearance. Different types of rust fungi infect different tree species.
Different types of rust fungi usually have names that include the type of tree they infect. For example, some varieties include ash rust, cedar-apple rust, pine stem rust and white pine blister rust.
In general, rust fungus has a yellow, orange or red rusty colour. Ash rust and cedar-apple rust show up as rusty spots on the tree's leaves. White pine blister rust and stem rusts show up as growths or rust-coloured wounds on tree branches or trunks
Rust fungus may kill some branches on conifers. Ash rust usually does not damage a tree severely, but it can make it more likely to sustain damage from cold winter temperatures. Apple-cedar rust can damage fruit on apple trees.
Fungicide sprays can help kill rust fungus, and gardeners can prevent the fungus by making sure to purchase healthy trees from certified nurseries.