What Fungicides Can I Use to Control Rust Spots on the Leaves of Black-Eyed Susans?

Rust Symptoms

• Black-eyed Susans that have contracted rust exhibit rust-colored spots on their foliage and stems. Sometimes, spots appear on the underside of leaves. The areas around the spots are discolored and yellowed. Furthermore, black-eyed Susans are generally unable to produce healthy growth. Rust is controlled with fungicides. However, it is important for gardeners to use fungicides that specifically target the fungal spores that cause rust disease. Also, certain cultural practices prevent these fungicides from causing further harm to your black-eyed Susans.

Sulfur

• Sulfur fungicide is used to treat rust on black-eyed Susans. Gardeners apply this fungicide by spraying their ornamental plants. Mix up 2 to 2-1/4 tbsp. of sulfur with 1 gallon of water. Spray your black-eyed Susans evenly with the sulfur mixture. Repeat the spray five to 10 days after the initial application and after it rains. This fungicide easily washes off during rainfall and irrigation. Avoid watering your black-eyed Susans from overhead when using a sulfur fungicide.

Mancozeb

• Mancozeb is a broad-spectrum herbicide that is used to treat rust and other fungal-related diseases. Before using this fungicide product, shake up the bottle. Mix 3 tbsp. of mancozeb with 1 gallon of water to spray on plants. Cover the underside of leaves and along their stems before spraying black-eyed Susans. Apply mancozeb every seven to 10 days as soon as you see rust symptoms for effective control.

Care

• Avoid using your rust fungicide during intense heat to prevent dehydrating your black-eyed Susans. Keep up a watering schedule. Fungicides should not be used on water-stressed plants. You can help remove fungal spores by pruning off some of the heavily infected leaves using bypass shears. Clean up any plant debris underneath your black-eyed Susans. Debris left underneath the plant results in your black-eyed Susans getting reinfected with the disease.