Rust

Rust is a parasitic fungi that affects a wide variety of woody and herbaceous plants including apples, crabapples, hawthorns, and roses. Even though it rarely kills a plant, it reduces a plant's health and flower production. 

There are different types of rust diseases; however, the defining characteristic is the appear of spots, or spore masses, that resemble rust or iron oxide. Yellow or white spots from on the upper leaves, and reddish to orange blister-like swellings form on the undersides of the leaves. Often, the leaves to twist or distort and drop prematurely. 

Needing a living plant to survive, rust is spread by spores that are transferred from infected plants to healthy plants. These spores can be transferred either by the wind or by water, which is why rust disease often spreads after watering. 

The following can be done to treat rust and prevent rust:

• Remove all infected plant material from the plant and the ground and apply a liquid copper fungicide. 
• Water trees and shrubs at the base and be careful not to splash water on leaves. A drip line or soaker hose works best for this. Avoid watering plant with sprinklers.
• Applying fungicides in the spring, can reduce some rust disease.