Rust-Colored Spots on Hibiscus Leaves

Rust

• While there are over 5,000 different fungus species that cause rust, Kuehneola malvicola is the species that infects hibiscus plants, according to the Florida Department of Agriculture and Consumer Services. In order for the fungi that cause rust to germinate and spread, they need moisture for six to eight hours, according to the University of California. Once hibiscus leaves have been infected with the fungal disease, spores can spread over the rest of the leaf.

Symptoms

• Rust causes orange-brown pustules to form on the underside of hibiscus leaves, according to the Florida Department of Agriculture and Consumer Services. The tops of hibiscus leaves typically develop yellow-brown spots. As the disease progresses, leaves defoliate and the entire plant declines in health. Hibiscus plants without leaves have a difficult time photosynthesizing. Because rust easily spreads from hibiscus plant to hibiscus plant, move any infected plants away from the rest of your garden.

Cultural Control

• Prune off infected leaves with a pair of bypass shears. Sterilize the shears before using with a mixture of 70 percent denatured alcohol and 30 percent water. Clean up diseased debris underneath your hibiscus plant. Throw away or burn diseased debris. Avoid placing debris in your compost. You can prevent spreading rust by watering your hibiscus plants at their base, as recommended by the University of California. Overhead water promotes the germination and spread of fungal spores.

Chemical Control

• Treat diseased hibiscus plants with a fungicide that contains active ingredients such as mancozeb, triadimefon, propiconazole or azoxystrobin, as suggested by the University of California. Spray the hibiscus evenly with the fungicide to coat the tops and bottoms of leaves. Keep our hibiscus plants watered when starting a fungicide program. Water stressed hibiscus plants can become harmed when sprayed with fungicide. Follow the directions on the label. Gardeners must spray their plants accordingly in order for the fungicide to be effective.