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2 Ways To Treat Rust Spots On Indoor Plants

Among the many diseases that attack houseplants, rust plant disease is where a small outbreak that is often ignored spreads rapidly. Though they do not kill the plants in most scenarios, they can significantly reduce their growth and affect their health.

Rust disease is caused due to a particular group of fungi that survives by feeding on living plants. Moist conditions around prolonged wet leaves and high humidity accelerate the spread of the fungus. Trimming off the infected parts, chemical sprays, and improving the growing conditions might help.

In this article, we will study this pathogen, the conditions that cause them, ways to identify the infection, and the prevention and treatment. 

Leaf rust

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What causes rust?

Rust is the reddish-orange flakey substance that forms on old unused iron due to oxygen and moisture reactions.

Though rust occurs mostly on leaves, sometimes the stems and even fruits and flowers may start showing signs of infection.

It is a disease that harms your plant and is caused by a fungus attacking your plants.

Though they are more commonly seen on roses, tomatoes, beans, pines, etc., they can attack almost all kinds of plants, including those growing inside our homes.

Fungi cause them from the pucciniales order, and their size is less than ½ inch in diameter.

The spots that are formed on the leaves are powdery.

So if you dab cotton or tissue to check whether it is rusting, the color will be transferred to the cloth.

Rust on plants

High temperatures and high moisture are some factors that promote rust disease.

The infection begins when a rust spore that travels through water or wind invades a plant and germinates on the host plant.

This fungus has cells that transport the nutrients from the plant to its own body.

The initial signs of rust come as specks of orange, rusty brown, and red-colored on your leaves.

As you leave the plant untreated, the spots begin to get bigger and gradually end up covering your plants in a bumpy-looking blister-like formation.

Further left ignored, these blister-like things break open, which releases spores that are further spread among the other plants by wind and water.

As these spores travel to other plants, they infect them too.

They stay dormant for some time until the conditions become favorable for them.

The spores breed in a moist environment, so the plant’s lower leaves are infested first as they are close to moist soil and get less light and air than the upper leaves.

Rust in your plants may not kill your plant immediately, but over time the growth of your plants gradually declines.

The plant shows signs of concern like stunted growth, premature yellowing and browning of the leaves, drooping unhappy-looking plant, and dead branches that drop off.

Rusting, once attacked, can be tricky to get rid of.

Hot, humid, moist conditions are a prime target of rust-causing pathogens.

Changing the plant’s growing environment and bringing changes in the care routine can help to treat the issue.


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Identifying rust on plants

Leaf rust disease

Although most often rusting is caused due to rust fungus, there are other reasons too that can look similar to rusting.

Before treating, identify whether it is rusting or any similar problem:

  • Multiple types of leaf spot disease produce similar-looking spots on leaves that resemble fungal rust. They look very much like rust but are caused by other bacteria. They are either raised or depressed and create round-shaped lesions.
  • Brown spots on the leaves may also emerge due to incorrect growing conditions, wrong pH, fertilizer overdose, and so on.
  • Accumulation of salts from excessive fertilizing can lead to brown freckles on the leaves.
  • Pest infestations caused by spider mites in the plants can cause spotting like rust. Pesticides, rubbing alcohol, or soap solutions remove these bugs efficiently.
  • Nutritional deficiencies of calcium and magnesium also create rust-like spots.

Signs of rust damage

The signs of rust fungus come in different forms on different plants.

But what is to be remembered is that the rust fungus that attacks the plants looks similar to the rust that appears on old unused bicycles lying in the shed for a long time.

A plant infested by rust-causing fungi shows signs of infestation that include:

  • The signature sign of rust is yellow or white spots on the leaves on the upper side of the plant.
  • Reddish or orange blisters-like swelling known as pustules can be seen on the underside of the leaves.
  • Leaf distortion and defoliation occur.
  • Orange or yellow spots on the underside of the leaves.
  • Within these spots, spores are formed.
  • Plants infected by heavy rusting for a prolonged period begin to experience curling and withering of leaves.

Treatment of rust fungus on plants

There is no easy treatment to cure the plants that have started to rust, but you can deal with fungus in two ways:

1. Commercial fungicides

Use fungicidal sprays with copper formulas, organic sulfur, and fungicidal soap.

Do not use sulfur when the temperature is too warm, as that can affect the plant.

Follow the instructions closely about the usage.

There are several commercial fungicides available in the market to control rust fungus.

Apply these at the first sign of rust damage.

The more you let it advance, the more difficult it gets to treat.

Look for the fungicides with these active ingredients: Mancozeb, Trifloxystrobin, Chlorothalonil, Myclobutanil, etc.

2. Control by organic methods

In case you do not have access to fungicides, you can make homemade solutions to treat the problem.

Every week dust some sulfur on the plants affected by rust fungus.

Neem oil, an organic fungicide, can be sprayed every 4-5 days.

The performance of baking soda will enhance if you spray this mixed with light horticultural oil.

A solution with one teaspoon of baking soda to a quarter of water.

Or ½ cup of minced garlic to a quarter of water.

Some plant owners also swear by aspirin spray mixture to treat their rust-infected plants.

Use standard 325 mg aspirin tablets with water and spray it all over the plant.

Repeat the solution every five days until you see results.

Other tips for treating rust on plants

money tree mist and brown

Here are a few other ways to treat rust disease plants:

  • Trim or prune off any affected plant parts as soon as you notice any signs of rusting. The earlier you spot them, the easier it is to cure.
  • Remember to sanitize your pruners before and after use. Otherwise, the fungus can spread if you use them on another healthy plant. To sanitize the shears, using a mild bleach or isopropyl alcohol works, and after cleaning, dry them in sunlight.
  • Please get rid of all the debris around the plants after cleaning them. Many plant owners use this debris containing plant rust or fungus in the compost pile to burn the spores. It is, however, not recommended to do that, as some rust spores can even overwinter. It is best to discard them or burn them off immediately. 
  • While watering the plants, be extra cautious not to let the water splash on the leaves. Water just the soil, and ensure the leaves stay dry. 
  • Water during the early mornings so that the plants get enough time to evaporate the water. 
  • Do not mist the rust-stricken plants, as wet leaves encourage the germs to breed.
  • Maintain good airflow around the plant. Poor ventilation and a damp and humid environment can cause multiple problems in plants and treat severe problems. Ensure the conditions are drier.


Prevention of rust on plants

It is easier to prevent the rusting problem than to fix rusting from your garden because it is difficult to eliminate once it sets in.

Try the below steps to discourage the formation of rust in your plants:

  • The target of rust is damp, moist, humid conditions. Incorrect watering is a prime cause that attracts this fungus. Drip irrigation or a soaker hose to water your plants keeps water from splashing on the foliage. As a bonus, it also reduces the wastage of water.
  • Whenever you water your plants from overhead, make sure you do so in the mornings so that the water gets evaporated throughout the day. Watering in the evening or night is not recommended because the water keeps the foliage wet all night, making it a breeding ground for germs. Keep the leaves of your plant dry at all times. If there is water, ensure sufficient light and air to dry it off. 
  • Certain plants are more prone to getting infected by these rusts. Do some research and get plants that are more resistant to the fungus. When possible, buy plants that are more resistant to rust.
  • When you buy a new plant, examine it carefully. Buy from reputed and trustworthy sellers only. Do not bring home plants that are already sick or infested. After bringing it home, keep the plant isolated from other plants for about three weeks so that if any germs are there, they do not spread to other plants.
  • Maintain sufficient ventilation around the plants at all times. Maintain space between each plant, so there is good air circulation. Cramping them together encourages the breeding of fungus as ventilation decreases. 
  • Regular prune your plants to maintain their health and appearance. It also helps to improve airflow between the leaves and reduces the chances of infections. 
  • Before using any tools on your plants, sterilize them to kill any germs that might have attached to them. 

How should I water plants to prevent rust fungus?

Schefflera soggy soil and overwatering

Rust fungus thrives in wet moist conditions.

They sit on wet leaves for 6-10 hours before they infect the plant.

If your plants undergo rust fungus, you must stop overhead watering.

Use drip irrigation or a hose to water.

If this is not available, water during the early morning so that throughout the day, the water gets dry with the help of sunlight.

When soil slashes on leaves during watering, it is a sign of infection.

Is rust fungus toxic to humans?

Rust fungus is not toxic or poisonous to humans or animals but eating food with rust is not recommended as the flavor of the food turns off. 

Final words

Rust disease is found in many houseplants. If you find your houseplant attacked with rust fungus, do not panic. Use organic methods or commercial fungicides to fix the issue.

Inspect the plant thoroughly and find out if the plant is experiencing rust disease. Sometimes, the plant can undergo other diseases that may appear, like rust disease.


Reference: Department of Plant Pathology and Ecology, Plant Disease Detection, Research in Plant Disease.