Can dish soap sprays treat rose rust?
Written by
Olivia Mitchell
Reviewed by
Prof. Martin Thorne, Ph.D.Dish soaps play a supporting role in rose rust treatments, helping fungicidal mixtures adhere to leaves. Still, they are never used alone in the treatment of this disease. Mild liquid soaps like Castile help treatments just a little and do not hurt plants, while degreasing dish soaps cause permanent coating of the leaves, which results in injury. With 18 years of experience as a horticulturist, I have observed that only mild liquid soaps like Castile do this.
Appropriate Soap Types
- Castile soap: Plant-based, pH-neutral formulas
- Insecticidal soaps: Potassium salt blends designed for plants
- Baby shampoos: Mild surfactants without degreasers
- Avoid: Dawn Ultra, Palmolive Oxy - contain harsh degreasers
Mixing Guidelines
- Standard ratio: 1 teaspoon mild soap per gallon solution
- Combination: Mix with fungicides like neem oil first
- Water temperature: Use lukewarm water for better emulsion
- Testing: Apply to single leaf first checking for damage
Risk Management
- Degreaser damage: Strips protective leaf cuticles within hours
- Salt buildup: Causes leaf margin burn after repeated use
- Beneficial harm: Kills predatory mites and ladybug larvae
- Phytotoxicity: Maximum 3 applications per month maximum
Use soap-based solutions at dawn with a fine mist sprayer to get even coverage. Cover the undersides of the leaves thoroughly where rust develops. Repeat every 7-10 days during outbreaks. Use nitrile gloves for spraying and avoid bloom periods to protect the pollinators.
Watch for buildup of soap residues, sometimes observed as white streaks on the foliage. After 4 hours, wash the leaves with clean water. Watch for signs of phytotoxicity (curled edges of leaves or discolored veins) that indicate the need for immediate discontinuation of the treatment.
Store detergent concentrates in cool dark places and away from light. Make a good label for the containers that will record the dates they are mixed. Any unused mixtures should be discarded after 48 hours, as their effectiveness is significantly impaired. I keep only small batch sizes in the refrigerator, which are reserved for emergency spot treatments.
Read the full article: Comprehensive Rose Rust Treatment Solutions
