Rust

​Rust doesn't just mean 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 (Kate Russell)

There are several different strains of rust that attack a variety of garden and ornamental plants:

• almonds - Tranzchelia discolor
• asparagus - Puccinia asparagi
• beans - Uromyces appendiculatus, Uromyces phaseoli typica, and more
• caneberries - Kuehneola uredinis, Phragmidium rubi-idaei
• cedar, cypress, and juniper - Gymnosporangium spp.
• garlic and onion - Puccinia porri
• peaches and other stone fruits - Tranzschelia discolor
• pears - Gymnosporangium libocedri
• roses and chrysanthemums - Puccinia spp.
• turfgrass - Puccinia striiformis, P. graminis, P. coronata, and Uromyces spp.

This is only a partial list, but you get the idea.


How rust grows

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


How to control rust

Rust is easily spread by ants, aphids and garden tools. If you find a leaf infected with rust, remove it and throw it in the trash. It is a good idea to remove any leaves below the infected leaves, as they have already been exposed to fungal spores, which will begin developing soon. Good airflow, aphid control, and avoiding overhead watering are your best rust control measures. You can also apply sulfur or other fungicides. Just be sure to completely cover every surface, especially the underside of leaves.


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