Hosta plants are a perennial plant that has attractive foliage and is common in many home gardens. It is a hardy and versatile plant that normally requires very little maintenance. However, the hosta plant is susceptible to some diseases that have varied symptoms, including rusty discolorations on their leaves.
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Rusty discolorations on hosta plants are attributed to several different fungi. These fungi include Anthracnose, Phillosticta, Cercospora and Alternaria. Each of these fungi can produce dark brown and rust-colored spots on the hosta leaves, but Cercospora and Anthracnose are more likely to produce brightly colored rusty spots, as well as rust-colored leaf borders. All of these fungi can lead to leaves becoming spotty and unattractive, but rarely cause death.
Fungus is more likely to affect a hosta when conditions are damp and humid. If the leaves are wet for long periods of time, they can easily develop fungus. Frequent dew and improper irrigation that keeps hosta plants wet constantly can also lead to fungus. Watering plants later in the day when it is warmer can also lead to the presence of fungus.
Plant fungicides are usually effective against fungus that leaves rusty discolorations on hosta leaves, but in the case of Anthracnose, the fungicide should be put on leaves where there is not yet any fungus. Hostas can also be watered in the morning so the water has plenty of time to evaporate before nightfall, and care should be taken to ensure hostas are not constantly being soaked by sprinklers or other activities.
Daylily rust is a disease normally specific to the daylily plant, which is caused by a fungus called Puccinia hemerocallifis. The plant results in rusty spots and streaks along the daylily leaves. While the fungus is thought to normally infect daylilies, the hosta plant is considered a possible secondary host that can develop the fungus, but not develop the associated daylily rust disease that goes with it.