Rusts

Rust diseases include over 5,000 species of fungi. Common hosts include roses and tomatoes along with many other herbaceous and woody plants. Monocultural ecosystems can be heavily impacted by rust making it an important disease to manage in agricultural and horticultural settings.

As the name suggests, rust diseases appear on foliage similar to rusty metal. They are common in temperate, moist conditions and only infect living tissue. Problems can spread quickly if plants are tightly spaced, foliage remains damp and/or infected plant material remains in the growing area. For this reason, control begins with proper planting, watering and sanitation practices.

What to Look For?

Infection is most common in areas where water splash touches foliage; however, spores are also commonly spread by wind. Damage begins as leaf spots, often yellow or orange, that may develop into pustules (blister-like structures) on the undersides of leaves. These pustules cause leaf distortions and can result in defoliation.

Controlling Rust: Prevention is the best way to control rust. Act proactively to avoid infection, particularly if you are growing rust-susceptible plants.

  • Proper plant spacing allows proper air flow and reduces the risk or plant-to-plant infection.
  • Avoid overhead watering and overspray.
  • Early season sulfur dustings kill spores before they infect plants.
  • B. subtilis based biofungicides (Cease) work well to suppress rust disease.
  • Oil sprays like horticultural oil and neem oil can be used as a last resort.