Rust found on plants refers to a disease caused by pathogens or fungi. There are various forms of rust, some specific to certain species of plant. Rust must rely on infecting healthy host plants to thrive and spread. While prevention is the best course of action, there are a few organic treatments that can help after an infection has occurred. If the disease is spotted early enough, simple pruning can stop the continued infection.
Rust is a fungal disease that is easily identified by color changes. Initial signs of the fungus appear as rust-colored spots along the top of the leaf. Color changes vary from yellow and greenish tint to orange with a reddish center. Look for bumps on the underside of leaves that correspond with the discolorations. The bumps are the spores of the fungus.
Rust fungus thrives on moisture. Look for rust to show during hot, wet weather when humidity is high. Overwatering plants can attract the fungus and fungal spores can travel via rain or wind. Splashes of water can transmit the fungus from the ground to leaves. Plants that are close together can form bridges where spores have little distance to travel and can spread quickly.
Determine if you have rust fungus on the leaves; look for signs in the early morning when weather is cool and dew points are high. If you spot discoloration, begin to inspect the underside of suspect leaves for other characteristics, such as bumps. Immediately remove diseased leaves, including those that fall to the ground. Put the leaves you removed into a plastic bag and dispose of these with normal garbage. Disposing of leaves using any other method may allow rust fungus to spread because the fungus can lay dormant in soil and compost until it becomes activated.
Treat heavier infections with a fungicide mixture containing chlorothalonil. Fill up a garden sprayer and apply the fungicide to the leaves following the manufacturer's directions. Cover the underside of infected leaves to destroy all spores. Repeated applications must be carried out weekly until the presence of rust fungus is no longer evident. Remove all plants that remain heavily infected. The best time for treatment of heavy infection is when temperatures rise above 82 degrees Fahrenheit. Destroy all plants that were infected at the end of the growing season; tilling or composting these plants back into the soil may release any remaining dormant fungus.
A natural treatment can be made using garlic. The rust fungus cannot tolerate sulfur, which is found in garlic. Blend a quarter pound of garlic with one quart of water in a blender for 10 minutes; add drops of dish liquid to the mix, and strain the liquid to remove the chunks of garlic. Advanced infections will require this mixture to be applied at full strength; lesser infections can be treated by using one part solution with nine parts water. Spray the solution onto the leaves and then the entire plant.
To avoid an onset of rust fungus, keep moisture levels at minimum required amounts. Let the top layer of soil dry before watering plants so the fungus cannot be supported in the soil. Dry the leaves to eliminate the breeding ground for spores. Give plants room to breathe; this allows plant leaves and soil to dry properly. Dispose of all garden waste to avoid providing the fungus with a location to lay dormant.