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What Causes Rust Disease on Plants? and How to Treat Them?

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Gardening has been a passion and hobby of millions across the centuries. Growing plants brings peace and joy, but for those who love plants, there is nothing more saddening than watching plants die due to an infection. Many different kinds of fungi and bacteria affect plants. One of the common fungi species that affects thousands of plant varieties across the world is rust.

What causes rust disease in plants? A fungal parasite causes rust disease. This parasite spreads through the host plant destroying its cells from within. It is more prevalent in humid, warm conditions. It will spread via spores carried on the wind from infected to uninfected plants. Poor garden husbandry can make this situation worse.

The rust fungus is a pathogen that relies on the host body to fulfill its needs. A rust infection can be a big headache and extremely difficult to get rid of.

More importantly, severe infections can lead to lethal plant deformities, including witch’s broom, galls, and hypertrophy. Thus, gardening experts worldwide recommend taking proper preventive measures regularly to keep this fungus in check, not allowing it any time or optimal conditions to grow.

close up of rust disease

In this article, we will discuss everything that all plant lovers must know about the rust fungus — its lifecycle, symptoms, and treatment. So, if you have experienced a rust infection or are currently dealing with one, read on.

What is rust?

Rust is one of the most harmful and dangerous pathogens and is, thus, rightly considered a menace to your garden. A plant disease that is known to attack white pine, soybean, wheat, coffee, snapdragons, beans, tomatoes, roses, leeks, and various other plants. Rust is caused by more than 4,000 species of fungi and fungus-like organisms that affect over 5000 species of plants.

The fungus is called rust fungus, which most commonly leads to brown spores on plant surfaces. However, in some cases, the infection caused by rust may manifest as red, orange, yellow, black, or brown spots. In the beginning, the spots caused by the Rust fungus appear as white-raised spots, turning into reddish-orange or brownish spore masses.

If left untreated, these spores eventually become black, infecting the entire leaf and causing it to wither and fall. Rust affects only living plants, and the infection limits itself to plant parts, such as leaves, stems, tender shoots, fruits, etc. Further, different types of rust species are named after the plant they infect. For instance, the white pine blister rust gets its name from the plant species it affects, i.e., white pine.

Similarly, the rust fungi that affect coffee is called Coffee Rust, and the fungi species that affect cedar apple is called Cedar Apple rust. The rust fungus has a complicated life cycle; within a single life cycle, it can infect two different plant hosts.

What conditions does rust require to grow

High light intensity, high moisture, and high temperatures are some of the factors that promote rust growth. Therefore, the best way to keep this fungus away from your gardens is to ensure it does not get the optimal conditions it needs to grow.

A rust infection begins when a rust spore lands on the surface of a plant, germinates and infects the host plant. The infection causes the plant to appear yellow and stunted in growth. Since rust grows intracellularly, the more severe infection cases manifest in rust-fruiting bodies.

A rust infection can turn out to be lethal to plants’ health. Severe infections can lead to proper plant deformities, such as witch’s broom, galls, stem canker, and hypertrophy.

How does a rust infection spread?

To protect plants against rust infections properly, gardeners must first understand how a rust infection spreads in the first place.

The rust fungus usually spreads through the wind, water, or insects. When a rust spore lands on a susceptible plant, it begins infection by producing a short hypha called the germ tube. This tube locates one of the many minute pores present on the epidermis of the leaf, which it uses to enter the plant leaf.

Once the germ tube has located a pore, it spreads the infection to the plant body by producing an infectious structure called an appressorium, through which the infection passes into the plant body. Since rust is a pathogenic fungus, it produces more germ-tube-like structures once inside the plant body.

These structures contain H+-ATPases, which transport nutrients from the plant body into the fungus. The fungus continues to infect the plant until spores begin to appear on the plant’s surface. The Rust fungus repeats its process of infection after every 10-14 days and, in the process, spreads the infection to various parts of the same plant or new hosts.

rust disease on leaf

How to identify a rust infection?

The symptoms of a rust infection are quite easy to read. By regularly checking the plant leaves, gardeners can identify a rust infection in time and stop it from spreading. Though rust diseases affect a variety of plants, how the symptoms of this infection manifest themselves remain more or lesser similar in all plant species.

The fungus goes through different stages in its lifecycle and ultimately physically manifests itself in the form of yellow, orange, and brown powdery pustules. In case of severe infections, the color of these blisters or pustules can also change to black or purple-brown.

If you think rust has affected your garden or plant products, you first must check for blister-like swellings or spots on the underside of the leaves. Most likely, these spots will be either yellow or orange. Similarly, rust infections manifest themselves in white or yellow spots on the top leaves of a plant.

If you have been experiencing defoliation, a rust infection could be the main reason because when a rust infection spreads, the leaves turn dry and fall from the plant. In conclusion, keep an eye out for any blister-like appearances on the leaves of your plants.

What can I do to prevent rust?

The rust fungus uses air, water, and insects to spread itself and, thus, can quickly spread. It is, therefore, better to practice prevention than cure. Here are a few simple tricks to keep rust infections away from your gardens.

  • Rust grows rapidly in wet conditions. Thus, the best way to protect your plants from rust fungus is to stay clear of overhead watering. Instead of watering your plants using a hose, use a drip irrigation system and water only the roots.
  • If you do not have access to a drip irrigation system, clean your plants early in the morning. This way, the sun’s heat will make the water evaporate quickly, thereby naturally reducing any chances of rust infection by removing any excess moisture.
  • While planting seeds, make sure there is ample space between all your plants. If you keep your plants in pots, there should be plenty of space between every pot. Since rust uses air, water, and insects to spread itself, proper spacing reduces the chances of the infection spreading. Further, this arrangement also creates space for disease spores to fly away from the garden.
  • These days, hybridizers are continually working on developing rust-resistant plant varieties. If the problem of rust has plagued you and your garden before, it’s best you invest in rust-resistant varieties of plants and flowers. However, always leave ample space between plants, irrespective of the plant variety you plan to cultivate.
  • Regarding rust prevention, sulfur is one of the most effective agents. Thus, make sure to invest some money in a light sulfur spray and spray it on your plants and flowers every week. In case you do not have sulfur, try neem oil.
  • Neem oil is a natural fungicide that is very effective at controlling rust. It is also easily available in the market. Conversely, you can also use a mixture of baking soda and low-intensity horticultural oil to keep the rust away from your garden.
  • Regularly prune your plants to get rid of any infection. Pruning also leads to better air circulation, reducing the chances of an infection spreading to other plants. Make sure to clean your tools when you prune your plants or rake the soil. Infected tools are one of the quickest ways infections spread themselves.
  • Make sure to rake the soil before planting any seeds. Further, once you are done raking, cover the soil with mulch. The mulch does an excellent job of preventing the spores from splashing back onto the leaves.
  • Most rust fungus varieties are host-specific. Thus, rust can easily be prevented by practicing plant rotation, although this is not always the case. Rotation may help if you keep having problems with rust on a particular variety.
branch for of leaves affected with rust disease

Make homemade fungicides that can deal with rust.

Rust diseases are not uncommon, and they affect a variety of plants. The disease or infection leads to the appearance of yellow, orange, and brown spots on leaves and can also lead to foliage withering and other deformities. This article discusses some prevention techniques that plant lovers can use to keep rust fungus away.

One of the easiest ways to keep rust at bay is to use effective fungicides regularly. It is quite easy to find commercial fungicides these days. However, many people prefer making fungicides to tackle the problem of rust. So, here are a few simple homemade sprays that you can use to control rust.

  • Homemade Baking Soda Fungicide
  • Homemade Sulfur-Based Spray
  • Homemade Bordeaux Spray
  • Homemade Aspirin Spray

Homemade Baking Soda-Based Fungicide

Many people swear by using baking soda when it comes to rust infections. However, making baking soda-based fungicides must pay special attention to proportions. The excessive amount of salt present in baking soda can prove to be toxic for plants. To create your homemade baking soda-based fungicide, mix four teaspoons of baking soda to a gallon of water.

Add about six teaspoons of any light horticultural oil to this mixture. If you do not have a horticultural oil, add one tablespoon each of baking soda, castile soap, and vegetable oil to a gallon of water. Mix well, pour this mixture into a bottle, then spray it on all the plants using a sprayer. Repeat the process every week.

Homemade Sulfur-Based Spray

Sulfur has been used as a fungicide for decades now. It is a powerful protecting agent against rust fungus. However, sulfur is used as a preventive spray, not a treatment spray. In the market, sulfur is readily available in liquid and powder forms. The packing will also guide you in creating your homemade sulfur-based spray.

However, beware, many plant species do not react well to sulfur. Thus, read the instructions and ensure the plant species on which you are planning to use your sulfur spray won’t be negatively affected. Further, lime sulfur should never be used on foliage, and remember the best time to use this spray is right before or at the start of spring.

Homemade Bordeaux Spray

Bordeaux mixtures are effective against both fungi and bacteria. A Bordeaux mixture is essentially copper sulfate mixed with water and lime. Thus, to make your homemade Bordeaux spray, you must buy copper sulfate and hydrated lime separately, both of which are readily available online or at the garden center.

To create a homemade Bordeaux fungicide, mix three tablespoons of copper sulfate with ten tablespoons of hydrated lime and add a gallon of water. Mix well before pouring this mixture into a spray bottle and spraying on plants. Ideally, Bordeaux should be used on dormant trees and plants, i.e., during the winter season.

Homemade Aspirin Spray

An aspirin mixture is perhaps the easiest mixture to make at home. Mix eight aspirins with a gallon of water to create your aspirin-based fungicide. You should use the standard 325 mg aspirin tablets for this mixture. Mix well, pour the liquid into a pump sprayer, and spray it on foliage. The ideal time to use this mixture is right before spring.

the start pf rust disease on tree

Commercial Rust Infection Management

It is easy to prevent a rust infection by taking the appropriate measures. However, if, by any chance, you weren’t able to take the required preventive measures, which led to a rust infection, you must get an expert’s opinion. Once a rust infection has spread, getting rid of it can become quite difficult.

If not treated in time, a rust infection can ruin all of your plants. In the case of rust, the disease management plan for a specific rust infection depends on whether the disease is macrocyclic or demicyclic. In the case of macrocyclic diseases, the fungus has a repeating stage in its life cycle. On the other hand, in the case of demicyclic diseases, the fungus does not have a repeating stage.

In the case of macrocyclic diseases, the rust fungus either infects the host plant or the alternate host plant. For instance, the fungus that infects the white pine does not infect the white pine but its alternate host, Ribes. Thus, removing the alternate host is the perfect way to get rid of rust disease in the case of macrocyclic diseases where the fungus infects the alternative host plant.

On the other hand, if the fungus affects the host plant, the treatment involves resisting crops. For example, in wheat, the infecting fungus infects wheat itself and not the alternate host, i.e., barberry. Thus, getting rid of the alternate host is useless in the case of wheat. Experts get rid of rust infection by planting resistant crops in this case.

In the case of demicyclic diseases, since there is no repeating stage in the fungus life cycle, removing either the primary or alternate host is the only way to get rid of the infection. However, certain fungi survive even after removing the primary or alternate host. Thus, in this case, special techniques based on the plant type are used by experts to get rid of the rust fungus species.

If you have been dealing with a rust infection and have tried everything to make it go, but absolutely nothing has worked, it’s probably a good idea to get an expert’s opinion.

rust disease on grass blade

Conclusion

The rust fungus is a widely prevalent fungus — more than 4000 species of this fungus infect more than 5000 different varieties of plants. The good news is this fungus can easily be kept in check by following the simple preventive measures discussed in this article.

Further, gardeners must always keep an eye out for symptoms of rust infections. In case of an infection, remove or treat the infected plants immediately.

I hope you enjoyed this blog post about What Causes Rust Disease on Plants? I trust it answers your question fully. If this interests you, why not consider checking out some of my other blog posts and subscribing to the blog, so you don’t miss future content?

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Further Reading

Rust is the only disease that can affect plants in your garden. I have written some other blog posts covering some of the other diseases that may interest you. They are as follows if you would like to view them, click the links.

Remember, folks, You Reap What You Sow!