Rust Colored Spots on Hibiscus Leaves
The tropical hibiscus (Hibiscus spp.) plants growing in your garden provide visual beauty to your space with large, bold-hued blossoms often accompanied by equally vibrant, green foliage. However, when those attractive leaves display rust-hued spots, the cosmetic appeal of your plants begins to wane. The spots you are seeing are the result of an underlying disease that may affect the health of your entire plant. Put a control program in place immediately to prevent damage and to protect the health of your landscape.
Providing regular, appropriate care to hibiscus plants yields healthy plants with a heightened ability to avoid and recuperate from problems, such as disease. Hibiscus plants thrive in areas of the home garden that offer full sunlight but will tolerate light afternoon shade. For best growth, maintain moist, well-drained soil high in organic content. These flowering plants are hardy in U.S. Department of Agriculture plant hardiness zones 9 through 11.
The presence of rust colored spots on your hibiscus leaves is a symptom of a fungal disease referred to as hollyhock rust. Caused by the fungal pathogen Puccinia malvacearum, this type of rust disease affects a variety of plants, including hollyhocks, hibiscus and mallows. Spreading sporadically on wind and rain, the disease infects new leaf growth, making its appearance during the spring. Symptoms include tiny yellow pustules on leaf undersides followed by rust-hued spots on the tops of leaves.
As the disease continues to spread throughout the warmer months, infection grows across the leaves and may affect the stem and the green portion of any flower blossoms, explains the North Dakota State University Horticulture. The resulting damage includes cosmetically unsightly plants. In addition, leaves become infected quickly and die. When left untreated, hollyhock rust infects the entire plant and will continue to survive throughout the following seasons.
Controlling this disease is essential in saving your plant from decline. To prevent disease and decrease its intensity, improve circulation by avoiding crowding plants. Irrigate soil directly to avoid standing water left by overhead sprinkling; wet foliage provides an ideal environment for the growth of fungi. Neem oil, sulfur-based fungicides or a fungicide with an active ingredient, such as chlorothalonil, provides preventive control when applied to emerging leaves. However, avoid using sulfur-based products when temperatures rise above 85 degrees Fahrenheit, as potential leaf damage may occur. Remove and destroy infected plant parts as well as any fallen debris to improve the problem and prevent future infections in your garden.
- North Dakota State University Horticulture: Hibiscus
- Clemson Cooperative Extension: Hibiscus
- Colorado State University Extension: Hollyhock Rust -- Puccinia Malvacearum
- University of Vermont Extension: Hollyhock Rust
- University of California Statewide Integrated Pest Management Program: Active Ingredient -- Chlorothalonil
Tarah Damask's writing career began in 2003 and includes experience as a fashion writer/editor for Neiman Marcus, short fiction publications in "North Texas Review," a self-published novel, band biographies, charter school curriculum and articles for various websites. Damask holds a Master of Arts in English and creative writing from the University of North Texas.