Rust

Rust is more than oxidized metal. It is also the name of a deadly plant fungus.

Well, it’s only deadly if you let it get completely out of hand. But it can significantly reduce your harvest  and make plants susceptible to other diseases and pests.

Rust on rose leaves

Several different strains of rust attack a variety of garden and ornamental plants:

• Almonds, peaches and other stone fruits  - Tranzschelia discolor
• Asparagus - Puccinia asparagi
• Beans - Uromyces appendiculatus, U. phaseoli typica, and more
• Caneberries - Kuehneola uredinis, Phragmidium rubi-idaei
• Garlic and onion - Puccinia porri
• Pears - Gymnosporangium libocedri

While this is only a partial list, you get the idea.

How rust grows

Rust fungi thrive when temperatures are warm (65°F to 85°F) and conditions are damp, like most spring mornings. It is easy to identify. Look at the underside of leaves for bright orange, yellow, or red spots. These growths may start as tiny white bumps. Before long, they turn into clusters of little clumps. These clumps are pustules. They contain millions of fungal spores. These spores are easily dislodged and can spread to nearby plants.

How to control rust

Ants, aphids and garden tools can all carry rust to vulnerable plants. If you find a leaf infected with rust, remove it and throw it in the trash. Remove any leaves directly below the infected leaves too. They are probably already infected with rust spores, which will begin developing soon. Pruning and placement for good airflow, aphid control, and avoiding overhead watering all help prevent rust. You can also apply sulfur or other fungicides. Every leaf surface, above and below, must be sprayed for this treatment to be effective.

Always disinfect your tools after removing rust-infected leaves to avoid spreading the rust fungus to healthy plants.