Fungal rust disease commonly brings about orange, red, or yellow spots on plant foliage. Rust spots are fairly easy to treat if they are correctly identified early on before they have the chance to spread.
The brightly colored spots are repositories of reproductive spores of a variety of fungi from the Pucciniales order.
If left too long without treatment, the fungal spores can spread throughout the plant or even to surrounding plants on air currents or through shared water sources.
Table of Contents
Rust Spots on Leaves
Rust spots appear as a smattering of discolored blots on leaves and are caused by a fungal disease. The fungal spores need moist conditions to spread. Plants prone to rust spots should be kept in a dry environment. In order to treat plants with rust spots, you need to cut off all the affected foliage and quarantine the plant.
How to Identify Rust Spots on Leaves
There are a number of other reasons why your plant’s leaves might have orange discoloration or spots, so it is important to ensure that you have correctly identified the cause as fungal rust disease before beginning to treat it.
White spots on a plant’s upper leaves are an early sign of fungal rot. Leaves affected by the fungal disorder will eventually develop rust-colored blots with a diameter of approximately half an inch.
Fungal rust spores are powder-like in texture. Leaf distortion will occur in more severely affected plants.
If the fungus is left without treatment for too long, it will lead to black spotting of the leaf and eventually to leaf drop.
There are a few other conditions with similar symptoms, so make sure you are not confusing the rust spots on your leaves with signs of one of the following:
Rust-spot-like leaf discoloration can occur if a plant is in acidic soil.
If you think this can be the possible culprit, consider investing in a soil pH meter.
Some pests, like spider mites, leave marks that resemble rust spots.
If you notice marks on your plant’s leaves, inspect it for further signs of a pest infestation!
If a plant absorbs excessively high levels of sodium, potassium or magnesium, or a number of other nutrients, it will begin to show signs of nutrient burn.
Nutrient burn manifests as brown spots on leaves and may cause leaves to dry up and curl at the edges.
Causes of Rust Spots on Leaves
Fungal rust spots on leaves develop when fungal spores spread from one infected plant to another through air currents or water.
The fungus needs a moist environment to thrive.
How to Treat Rust Spots on Leaves
The first thing to do after identifying that your plant has fungal rust is to snip off all leaves that have rust spotting on them.
Then remove all fallen debris from the soil under the plant, as this may still carry the spores. You can either throw these leaves in the compost or into the regular waste bin.
If you decide to compost them, however, you will need to ensure that your compost reaches above a temperature of 140 degrees Fahrenheit (60 degrees Celsius), in order to kill the live spores.
Next, you will want to quarantine any affected plants so that any remaining spores cannot spread to your other plants.
Investing in a chemical fungicidal spray may also be a good idea. Copper sprays or fungal powders should be applied every 10 days until all symptoms of rust disease have disappeared.
Alternatively, you can make an anti-fungal solution at home.
The most important thing is to keep the environment your plant is living in free from unnecessary moisture.
Make sure to follow the prevention tips listed below, as these will also help your plant to recover!
How to Prevent Rust Spots on Leaves
Water early in the day
Watering your plants in the morning gives them the entire day to dry out, which makes it far less likely that their soil will remain soggy.
Soggy soil can lead to spores taking up residence on the lower leaves.
Water the soil, not the plant
Whenever possible, try not to wet the plant itself, but only to water its soil.
If its leaves remain dry, they are less likely to take up spores.
Allow sufficient time for the soil to dry to the appropriate level before rewatering, and make sure air can properly circulate around the plant.
Disinfect your clippers
Rust spots are the result of fungal growth, which means that tools that have come into contact with the spots may still have rogue spores on them.
Disinfecting your clippers, scissors or any other tools you use on the plant will prevent the transfer of spores from infected leaves to healthy leaves or to other healthy plants.
Use an anti-fungal solution
There are several effective chemical anti-fungal solutions that can be bought in most garden centers or plant stores.
Alternatively, you can make a homemade neem oil or baking soda solution.
Frequently Asked Questions about Rust Spots on Leaves
Are there rust-spot-resistant plants?
If rust spots are a recurring problem in your household or garden, it may be worth investing in some rust-resistant cultivars of your favorite plants. For instance, if you are fond of hollyhocks, you might consider growing Russian hollyhock or Figleaf hollyhock, both of which are more resistant to rust than common hollyhock.
How bad is it if a plant has rust spots on its leaves?
Rust spots are usually not life-threatening for a plant. However, if too many of a plant’s leaves become affected and go untreated, the plant may lose too many leaves to continue growing healthily. It is a good idea not to cut off more than 1/3 of a plant’s leaves at a time. If more than 1/3 of a plant’s leaves are affected, it may therefore be difficult to bring the plant back to health, and it may need to be disposed of.
Daniel has been a plant enthusiast for over 20 years. He owns hundreds of houseplants and prepares for the chili growing seasons yearly with great anticipation. His favorite plants are plant species in the Araceae family, such as Monstera, Philodendron, and Anthurium. He also loves gardening and is growing hot peppers, tomatoes, and many more vegetables.