Geranium: Rust
Photo by: R.S. Byther
Biology
Rust is caused by a fungus that lives on plants and plant debris. This disease can spread by wind-blown spores or infected cuttings. Infections occur easily if leaves are wet for 5 to 6 hours in mild temperatures (55 to 75 degrees).
Both leaf surfaces first develop white or yellowish spots, which enlarge and become blister like. The brown powdery pustules are often in target-like arrangement. The pustules occur mostly on leaves and less frequently on stems.
Severe infection causes yellowing and defoliation. Cultivars range widely in genetic variation of resistance, from highly susceptible to immune.
Management Options
See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.
Non-chemical Management
Select non-chemical management options as your first choice!
- Destroy diseased leaves and severely affected plants.
- Avoid wetting foliage, and water early in the day to allow for quick drying.
- Reduce humidity by spacing plants for good air circulation.
- Inspect new plants for disease symptoms.
Chemical Management
IMPORTANT: Always read and follow label directions when working with pesticides.
For more information on using pesticides visit :
- In certain situations, it may be useful to apply fungicides when rust first appears and at 10-day intervals (14-day intervals for Spectracide IMMUNOX), two to four applications per season.
- Apply sprays thoroughly, covering both upper and lower surfaces of leaves.
Approved Pesticides
If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.
Additional Image
Photo by: R.S. Byther
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Evidence of noncompliance may be reported through your local Extension office.