What Causes Rust Disease on Plants? Garden Tips 2024

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Rust, as in plants, is a fungal disease that affects a wide range of herbaceous and woody plants. Even though rust is seldom deadly, it looks ugly and can spread through your garden quickly, impacting the health of your plants. Once your plants are infected, there’s not much you can do except remove the affected areas and possibly treat the plant with a fungicide. 

Rust disease is caused by a fungal parasite that grows on living plants. These fungi have spores that are spread easily by the wind. They spread particularly easily in mild, moist conditions. All they need to start a new infection is a film of water on the foliage or another part of the plant. 

What is rust disease?

Rust is a disease that attacks many different types of plants from trees to vegetables and flowers. It isn’t a single disease, but rather a group of fungal diseases, all of which cause rust fungi that result in rust spots. 

Rust diseases are caused by a rust fungus that attacks various parts of bushes, flowers, trees, and other plants, including the foliage. It appears in various forms, depending on the specific rust disease. 

While most rust diseases cause yellow, orange, red, and/or brown rust spots, there is another fungus-like disease that attacks many herbaceous plants. This develops into waxy, chalky-white spots that become powdery pustules that eventually darken.

Like true fungal rust types, white rust is found on the underside of leaves and other parts of plants above the surface of the ground. Also known as a white blister, white rust is closely related to downy mildew. 

Robert Harveson, an extension plant pathologist at the University of Nebraska, Lincoln, points out that rust pathogens have a very complex life cycle. Many have different spore types and they need several different hosts to complete the life cycle. 

However, Harveson singles out red rust common on sunflowers and doesn’t rely on alternate hosts. Instead, it produces all its different spores on sunflower plants. 

This, in itself, makes it difficult for ordinary home gardeners to fathom the whys and hows that relate to rust. 

What causes rust disease in plants?

So what causes rust?

Rust plant disease is caused by moisture and a fungal parasite that changes as it develops. According to the University of Minnesota Extension, the various types of rust fungi have totally different spores that attack different host plants.

Typically, rust attacks when the weather is hot and humid. Then when it becomes hot and dry, the fungus starts to multiply, often at an alarming rate. 

The first infection in many gardens is caused by fungal spores that blow from other areas. They settle on the ground and are then spread when it rains or the garden is watered. 

How to identify rust disease In plants?

A wide variety of plants are susceptible to rust, including various trees, a whole lot of flowers, and even your lawn. The secret is to look for signs and symptoms all the time, especially in wet conditions. 

In the early stages, look out for spots on stems and the underside of leaves that are white and slightly raised. All these little rust spots contain spores. 

It won’t take long for every leaf spot to get covered with a mass of red-orange colored spores. As the leaf rust develops, the pustules on the leaves often turn a yellow-green color. 

You may see these on all the green parts of the plant including the stems, leaves, and the flower calyx. If you rub the spots gently over a white tissue, you will see yellow, orange, red, or brown-hued powder come off. 

If you don’t do something about it, these rust spots are likely to turn black eventually.

Some rust diseases produce tiny spores that are cup-shaped. Rather than being powdery, they tend to produce more solid structures on infected plant leaves. 

Sometimes, dark lines and more dots form around the edges of the disease-caused spots. These are hard “survival spores” that develop as the plant’s rust disease develops.

Often rust plant disease stunts the growth of plants. Badly affected leaves often turn yellow and fall off. In severe cases, plants die. 

How do you prevent rust on plants?

Good air circulation around plants helps to prevent rust spot diseases. 

Space your plants well to ensure there is good air circulation between them. If planting from seed, be sure to thin them out once the seedlings start to grow. 

It also helps to divide or thin perennial plants when they become overgrown. 

Since rust is caused by moisture on plants, avoid overhead sprinklers and wetting the plant leaves when watering. Rather opt for a soaker hose or drip irrigation. 

Also, try to water in the early morning to allow the parts of the plant that do get wet to dry. Water until the soil is moist (not saturated) to a depth of about 6-9 inches. Don’t water again until the top 3-6 inches of soil is completely dry. 

Another useful tip is to avoid the use of fertilizers that contain nitrogen. Rust tends to thrive on the soft, lush growth that nitrogen produces. 

How do you treat or control rust on plants?

If you spot any kind of rust disease plants are suffering from, there are lots of effective rust fungicides available. If you identify the fungal parasite early, try dusting the affected plants with sulfur to prevent the infection from spreading. 

Once rust diseases set in and establish themselves, it’s best to remove all infected parts of the plant. Destroy them. Don’t be tempted to put them into a compost pile otherwise, the rust fungi will just continue to spread. 

Treat any remaining rust spots with fungicide. Just be ultra-careful with anything toxic when treating vegetables, even the parts you aren’t going to eat. 

If you don’t do anything about rust spot diseases, the badly infected leaves will eventually turn brown and fall off. This horrible rust plant disease also results in stunting the growth of plants. 


Rust is a common fungal disease that is difficult to eradicate. But it isn’t that hard to control. 

These garden tips will help you identify rust disease on your garden plants. They also suggest ways to both prevent and control rust fungus.  

If you are struggling to eradicate rust or control it, consider removing all the plants that are attacked and replacing them with rust-resistant cultivars.

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