Rust on Roses: What It Is and How to Treat It

Rust on Roses What It Is and How to Treat It

Roses are so loved that when settlers came to what would become the United States, they brought some of their old world roses as part of their most important possessions. The colonizers also discovered the roses native to North America and these were eventually shipped back to Europe for cultivation and breeding. 

Roses have been adored for thousands of years and have been a lasting feature of religion, art, fashion and, of course, the making of perfume. Napoleon’s wife Josephine was an avid collector, and roses were a status symbol that showed off wealth and good taste. That today’s average home gardener is able to grow roses is a blessing that many people of the past could not ever imagine having for themselves. 

Rose gardeners know the joy and beauty that blooming season brings, but they also know the heartache of seeing their plants fall prey to disease and illness. Rose gardeners need to know how to check for early signs of disease and how to handle it once it is identified in order to keep their plants in top condition and blooming happily. In this article, we will focus on the fungus known as rose rust, how to identify it and how to treat and prevent it.

what is rose rust

What Is Rose Rust?

Rust on roses is caused by a fungus called Phragmidium. There are currently nine different species of the Phragmidium identified. Unusual for a plant fungus, Phragmidium only infects roses and some varieties and cultivars are more susceptible than others. 

The rose rust fungus needs a living rose plant to live out its life cycle and will die out if there are no roses in the landscape. Rust fungus will overwinter in debris and dead material under rose bushes and the spring breezes can carry it to new plants. Rose rust will weaken a plant, and can even kill them if not treated early. 

Rose rust is possible anywhere in the U.S., but it is currently a much larger problem on the West Coast. Changing weather patterns and generally warmer weather is causing rose rust to appear in areas where it was not previously present. Greenhouses and nurseries can be prime breeding grounds for rust. This means that rust fungus can also be brought into the garden by the purchase of new plants which are carrying the spores.

Like most fungi, rose rust likes humid or damp conditions and thrives at temperatures between 64 and 69 degrees Fahrenheit. Rose rust is usually first noticed on lower leaves since the fungus tends to be at ground level and the spores will travel onto the plant by being splashed up in water droplets. The fungus will then travel upward on the plant. 

How to Identify Rose Rust

Often, the first sign of rust is yellowing or curling leaves on the lower portion of the plant. The tops of leaves may show yellow spots which become darker and can become black with time. Black spot on roses is another, more common fungal infection on roses and you can tell the difference when you look on the underside of the leaves. In the case of rose rust, you will find orange spots, called pustules, on the bottom of the leaves as well as on the canes (the stems of the rose plant). 

Learn More About What Can Affect Roses

The orange pustules will appear powdery and carry the spores of the fungal infection. The most likely time for rust to show itself is in the fall and the spring when the temperatures are a bit cooler and the humidity is higher, though rust can appear at any point during the growing season. 

The orange powdery appearance of the fungus is indicating that it is creating more spores and will be most contagious at this point. The life cycle of the fungus repeats every 10 to 14 days and will spread quickly during this time. Older, more mature leaves will be the first to show signs of rust, but new leaves will be infected as the cycle of the fungus goes on. 

Rose rust has five spore forms in its life cycle, but only a few of them are able to be seen with the naked eye. This means that even though you may have gotten rid of all the visible signs of the fungus, there may be spore forms that are hiding from view. As the weather gets colder, the fungus produces the spore forms that will overwinter in the leaf litter and the cycle can repeat again starting the next spring. 

While this all sounds very alarming and devastating, there are plenty of ways to treat as well as prevent rose rust fungus and keep your roses blooming beautifully for years to come. 

how to treat rose rust

How to Treat Rose Rust

Rust can be challenging to treat once it has become established, but it is not impossible. With some immediate attention and consistent follow-up, the home rose gardener should be able to cope with the situation. 

Remove Affected Plant Material

At the first sign of rose rust, the affected leaves and canes need to be removed. Being very careful not to touch unaffected rose plants while pruning out infected plant material, dispose of the pruned material immediately. If it is allowed in your area, burning the pruned material is the most effective way of disposing of it. Do NOT put this material in your compost pile and do not dispose of it in the woods. Affected material can be disposed of by burying it completely, or by sealing it in plastic bags and putting it out for garbage pickup. 

When working with infected plants, be careful to avoid touching other rose plants and wear disposable gloves. Also, make sure to wash your pruning tools before putting them away. As an extra precaution, wash the clothes you were wearing to remove any spores that may be on them. A trip through the dryer should destroy any spores that may have hitched a ride on clothing. 

Apply Fungicide to Kill Rust

Fortunately, there are many products available to help rose gardeners cope with a rust infection. After removing all visible signs of rust, the next step is to apply some sort of antifungal treatment. There are synthetic fungicides, natural antifungals and some home remedies that have been found to be helpful. 

Generally speaking, fungicides (chemicals that kill fungi) are better at prevention than they are at treating an established infection, but with vigilance, the home rose gardener can be successful. Look for products that contain an active ingredient such as triforine, myclobutanil, chlorothalonil, mancozeb or propiconazole. Follow the directions on the label very carefully and do not overapply these chemicals. Be sure to follow any precautions on the label to maintain the safety of you and your pets. 

Some rose experts recommend rotating between two or more different fungicides to reduce the chances of creating a chemical resistant infection and because some strains of the fungus will be more susceptible to certain fungicides than to others. 

Because of the life cycle of the rose rust fungal spores, you will need to treat with fungicides every seven to 10 days. 

hand holding rose leaf with rust

Horticultural Oil for Treatment of Rose Rust

Horticultural oil has been in use since the 1800s as a way to essentially suffocate overwintering insects, their eggs and fungi that may be harmful to perennial plants such as roses. These oils can be purchased for use in the home garden and can be mixed with other substances. There are also horticultural oils that have been created for use during the growing season as well. 

Read the directions closely and apply horticultural oil as directed and only after removing all visibly infected plant material. Some horticultural oils are damaging to ferns and coniferous trees so make sure to check that the areas you are spraying are appropriate for this treatment. 

Neem Oil for Rose Rust

Many home gardeners turn to neem oil as a treatment for infestations of mites, fungus and other plant diseases. Neem oil is distilled from the seeds of the neem tree and is a naturally occurring fungicide and pesticide. Used for hundreds of years as a treatment for agricultural issues, neem oil tends to have a sulfurous and garlicky smell.

Neem oil should not be applied if the roses are under stress due to drought so make sure to water them thoroughly a few days before applying the oil. Follow directions on the package and make sure not to apply neem oil when the temperature is over 90 degrees Fahrenheit. Neem oil should not be applied within 30 days of having treated the plants with any sort of sulfur product. Do not apply neem oil to wet or damp plants and make sure that the humidity levels are moderate. It is best to apply neem oil to a small test section of the plant and wait 48 hours to make sure that the plant can tolerate the treatment. 

how to prevent rose rust

How to Prevent Rose Rust

Now that we have covered how to treat rust once it has attacked your roses, we will go over some methods of prevention so that it will not become a problem again going forward. There are many simple methods to help keep your roses healthy that can not only help them avoid illness, but can lead to stronger plants and better blooms. 

Plant Roses in Full Sun

For most varieties of roses, more sun means more happiness. Better exposure to sun also helps keep vegetation drier and can even kill off fungal spores.

Space Plants Well

Plant roses so that they are well spaced for good ventilation as well as preventing the spread of disease. Rose canes should not be touching from plant to plant and this also allows the gardener access to the plant from all sides for maintenance and treatment. 

Water From Below

We can’t help where the rain comes from, but when watering roses, make sure to water at the roots or use a soaker hose system. Avoid splashing when watering to keep spore movement to a minimum. Save those sprinklers for the yard — or for the kids to play in. 

Only Work with Dry Plants

When heading out to prune, deadhead or collect blooms, make sure that the plants are dry. Working with damp plants is an easy way to spread fungal spores as well as other types of disease.

pruning rose bush

Feed Your Roses Well

Appropriate fertilization, watering and overall care will keep your roses strong and healthy. Healthy plants are better at resisting disease and can withstand more stress.

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Add to Their Microbiome

Lately, we’ve all been hearing a lot about microbiomes, which are the microscopic colonies of yeasts, bacteria and fungi that live on our skin and in our intestines that help keep us healthy. Plants have microbiomes, too, and the use of compost can help keep their microbiomes strong. Some gardeners create an aerated compost tea that they spray on the rose plants to help establish a protective colony of microbes on the leaves and canes. 

Fall Cleanup

Remove any debris and plant material from under your roses each fall as you put the plants to bed. This will help to remove any hiding places for fungal spores or other pests that may overwinter and attack in the spring. 

Plant Resistant Varieties

If rose rust is prevalent in your area or if you have struggled with it and lost, then consider planting some roses that are bred to be resistant to rust such as floribunda, musk and shrub roses.

Inspect Any New Plants 

When purchasing new rose plants, inspect them closely for signs of any sort of fungus or illness. Just to be super careful, quarantine new roses away from the rest of your plants for a few weeks until you are sure they are healthy. 

Regular Scouting

Make it a habit to look closely at your rose plants on a weekly basis during the growing season to check for any problems that may be starting. Caught early, rust and other infections are much easier to treat and it gives you an excuse to get out in the garden for a good walk-around every week. 

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