Tree Rust Disease Treatment


Tree rust is a fungal infection that attacks trees, with a particular focus on their leaves. There are thousands of different species of rust fungi, each of which is suited to a different type of plant.

All of these fungi have certain symptoms in common, namely:

  • Early Discoloration- Rust begins by leaving small discolored spots on the undersides of your plant leaves. These spots may appear white at first, but will gradually become darker, transitioning to shades of yellow, orange, red, and brown.
  • Budding Bumps- As the fungus spreads and darkens, it tends to protrude out from the leaves it attacks. You will start to notice small, discolored bumps.
  • Leaf Deformation- If you leave rust to fester for long enough, it will start to impact the health of the leaves. Leaves will wither, darken, and fall off, making it harder for the plant to obtain energy from the sun.

Tree rust is similar to lawn rust in its appearance and effect, but each is caused by a different species. Because the fungi that cause rust are specifically suited for each type of plant, you do not usually have to worry about disease spreading from one type of plant to another. But it can spread between plants of the same type, making it important for you to eliminate the fungus and address the conditions that caused it to spread as quickly as possible.


It’s not the same rust that you see on metal. There are over 5000 known species of rust found on plants. They are fungi that travel through the air to settle on a host plant.

Some of the common symptoms of rust include defoliation, stunted growth or branch dieback.

So… What is Rust?

It’s not the same rust that you see on metal. There are over 5000 known species of rust found on plants. They are fungi that travel through the air to settle on a host plant.


Rust is typically brownish-yellow to bright orange spots that form on leaves. The spots are filled with a powdery substance. This substance contains the spores that will spread to other plants if not treated.

Symptoms of Rust

Plants that have rust growth will not directly die from this type of fungi, but it can contribute the decline of the plant.

Some of the common symptoms include defoliation, stunted growth or branch dieback. Leaving your plant exposed to rust will surely infect other plants since rust is easily spread through the air.

Plants That Are Susceptible to Rust

There are over 7,800 known species of rust that affect plants and different species affect different types of plants. As a general rule, most plants can be affected by rust and the best course of action is at first sight, treat your plant with Safer® Brand Garden Fungicide, so you can eliminate the rust and prevent widespread dispersion.

Rust Controls


Sulfur or Copper fungicides, such as Safer® Brand Garden Fungicide, will help prevent rust from getting worse and help you control future outbreaks.


Sulfur or Copper fungicides change the pH balance of the plant, creating an environment where Rust and other fungal blights cannot thrive.

Generally, most solutions help with disease control because when the soil is healthy, (and not full of harmful chemicals) there is a never-ending battle between the good microbes and the pathogens and the microbes often win.

Carefully read and follow all instructions on the product packaging for safe and effective results. It is recommended with any pesticide to test plants for sensitivity to the product. Spray a small section of the plant in an inconspicuous area and wait 24 hours before full coverage.

IMPORTANT: Do not use products containing Neem Oil within 14 days of applying these fungicides. The mix of both products can greatly increase risk of phototoxicity (burning) to your plant.


Spray the fungicide when you notice the symptoms of Rust and then again as needed in 7 to 10 day increments. As a general rule, much like watering, do not use these products in the peak of the day or when temperatures exceed 90 degrees F to avoid wilting or browning of the leaves.

Fungicides can also be used as a preventative measure against fungal infections because the fungicide changes the pH of the plant and creates an environment that is not conducive to disease growth. Treatment once a month is recommended but in heavy rain seasons, treat every 7 to 10 days for best results.

Why Choose a Fungicide Solution?

Using fungicide solutions in your garden is an important step in controlling diseases such as rust.

Some ingredients, like the patented seaweed extract in our Safer® Brand fungicide products, actively increase a plant’s resistance to disease because it is a root growth stimulator, controlling many types of plant pathogens through increased biological activity. This is what many gardening experts refer to when they talk about the natural defenses of a plant and it is similar to antibodies in a human immune system.

Treating an infected plant with a fungicide is treating a symptom of the bigger problem. Keeping the living organism in the soil protected by using organic products that are compliant for use in organic production is not only good for the global environment; it also helps protect your plants from further outbreaks and other issues like insects.

Limit Rust Outbreaks With These Garden Tips


Make sure the soil around your plant is properly drained. Without proper drainage, your planting area can be a ripe breeding ground for disease organisms.


Adding organic materials through composting will generate beneficial microorganism activity which fights away disease and other garden problems.


Keep leaves as dry as possible. Water plants at the base instead of the leaves. Rust thrives in wet conditions.

Remove all diseased leaves or branches throughout the season and once again before winter. Remove all diseased leaves and canes from the plant and surrounding areas.

Safer® Brand leads the alternative lawn and garden products industry, offering many solutions that are compliant with organic gardening standards. Safer® Brand recognizes this growing demand by consumers and offers a wide variety of products for lawns, gardens, landscapes, flowers, houseplants, insects and more!

Watch out for rust that can jump from incense cedars to fruit trees

CORVALLIS, Ore. – Are globs of bright orange goo attacking both your incense cedar and pear trees?

You could be dealing with a potentially devastating fungus known as Pacific coast pear rust.

“On cedar trees, it looks like someone threw orange marmalade all over the tree,” said Jay Pscheidt, plant pathologist with the Oregon State University Extension Service. “It typically cycles from incense cedars to hosts in the rose family in early springtime, around the time that pears go through bud break.”

The fungus, also known as Gymnosporangium libocedri, must reproduce using two hosts — making its life cycle unique, Pscheidt said.

Its life cycle begins on incense cedar, which is not initially infected with the disease but carries it for three years. Bright orange goo with a jelly-like texture weighs down branches and produces airborne spores that float to nearby pear trees. These spores infect fruit and sometimes even green shoots and leaves.

Then those spores float back to the cedar and infect it with the same fungus, but now called a different name — “cedar broom rust.”

Pacific coast pear rust can thrive on any plant in the rose family. This includes the trees crabapple, hawthorn and mountain ash, as well as apple. It also includes the shrubs quince, serviceberry and wild roses.

Cedar rust can affect plants in western and southern Oregon. Since incense cedar is not widespread in the eastern and central parts of the state, it is not as much of a problem there.

“Wet weather is more favorable for rust diseases, and we saw a ton of it last year because it was so rainy in the spring,” Pscheidt said. “So far this year it’s a medium-level problem.”

The rust is not harmful to humans, but it deforms fruit and reduces yield. Cedar trees and rosaceous plants with numerous infections can decline and may die. Symptoms are most obvious in May.

A gardener’s best defense is to identify the rust’s alternate hosts, then remove the species from nearby areas permanently, Pscheidt said.

Spores can survive on cedar for three years, while living only for one year on rosaceous plants. New spores attack rosaceous plants annually.

There are no pesticide products available for home use to control the disease on incense cedars, according to Pscheidt. Gardeners can spray the pesticide known as Immunox on flowering pears.

The Pacific Northwest Plant Disease Management Handbook offers guides to Pacific coast pear rust and incense cedar rust.

The aliens have landed? All hail His Noodly Appendages? Shiny Tangela? Koosh gone wrong? Or is this one of those Japanese cartoons…?

Ok, none of those; it’s a fungus fruiting on the branches of that eastern red cedar. I saw this gall (and quite a few more) on a hike the other week in Ionia County while dodging rainstorms. It only looks like this for a few hours, and not just any red cedar can host it. The crazy thing is, when the spores from this particular fungus are “forcibly released” into the air, they aren’t going to go infect more cedars. They’re headed for nearby apple trees! This is just one part in a two-part life cycle, which is pretty bonkers.

Thanks Wikipedia!

This two-host system is where the fungus gets its name, cedar apple rust (named for the rusty lesions on apple leaves rather than the goo-bits on cedars). Obviously, the coolest part of this situation is when the telial horns get all orange and gooey after rain, because look at it!

The apple part of the life cycle is less showy, but more important to humans. The rusty spots on leaves are unsightly and not great for the tree, but if the spore grows on a young apple fruit, the fruit becomes “unmarketable” (agricultural code for probably not poisonous, but super gross) as it feeds the growing fungus. Then it releases a different spore that heads out in the wild world to find a cedar to bother.

Non-gooey stages of an awesome (if problematic) fungus. Clockwise from top left: rust spots on hawthorn leaves, dried out “cedar apple” after spore release, rust on an apple, first-year gall (before tentacles). Photos from Wikipedia and Cornell University

Though many orchards use anti-fungal preparations to prevent spores from growing on apples, an ounce of prevention is worth a pound of cure. Most apple orchards remove as many plants in the juniper genus from the surrounding area as possible to interrupt the life cycle.

There are a host of fungi in the same family that affect other fruit trees, like hawthorn, crab-apple, and quince with very similar results, but since most folks don’t grow them for profit, there’s not so much worry about them. Sorry fans of quince pie!

There are also, somewhat surprisingly, quite a lot of things in the natural world that require two hosts to complete their life cycle, like the trematode that gives you swimmer’s itch (using waterfowl and snails) and the bacteria that causes Lyme disease (deer and deer ticks). Not all of them are bad for humans, but we know the most about those because more people will give scientists more money to study them; weird how that works! Now go hiking after rain and find some jellyfish hiding in trees.

Best product
for Cedar Apple Rust

Cedar apple rust (Gymnosporangium juniperi-virginianae) is a fungal disease that requires juniper plants to complete its complicated two year life-cycle. Spores overwinter as a reddish-brown gall on young twigs of various juniper species. In early spring, during wet weather, these galls swell and bright orange masses of spores are blown by the wind where they infect susceptible apple and crab-apple trees. The spores that develop on these trees will only infect junipers the following year. From year to year, the disease must pass from junipers to apples to junipers again; it cannot spread between apple trees.

On apple and crab-apple trees, look for pale yellow pinhead sized spots on the upper surface of the leaves shortly after bloom. These gradually enlarge to bright orange-yellow spots which make the disease easy to identify. Orange spots may develop on the fruit as well. Heavily infected leaves may drop prematurely.


  1. Choose resistant cultivars when available.
  2. Rake up and dispose of fallen leaves and other debris from under trees.
  3. Remove galls from infected junipers. In some cases, juniper plants should be removed entirely.
  4. Apply preventative, disease-fighting fungicides labeled for use on apples weekly, starting with bud break, to protect trees from spores being released by the juniper host. This occurs only once per year, so additional applications after this springtime spread are not necessary.
  5. On juniper, rust can be controlled by spraying plants with a copper solution (0.5 to 2.0 oz/ gallon of water) at least four times between late August and late October.
  6. Safely treat most fungal and bacterial diseases with SERENADE Garden. This broad spectrum bio-fungicide uses a patented strain of Bacillus subtilis that is registered for organic use. Best of all, SERENADE is completely non-toxic to honey bees and beneficial insects.
  7. Containing sulfur and pyrethrins, Bonide® Orchard Spray is a safe, one-hit concentrate for insect attacks and fungal problems. For best results, apply as a protective spray (2.5 oz/ gallon) early in the season. If disease, insects or wet weather are present, mix 5 oz in one gallon of water. Thoroughly spray all parts of the plant, especially new shoots.
  8. Contact your local Agricultural Extension office for other possible solutions in your area.

Rust is a term used for a group of fungal species which attack a broad range of plants. The disease is usually seen on the underside of leaves where small rusty brown spores develop. Spores can be other colours, including orange and yellow, and can also occur on other parts of a plant. Infected leaves usually show yellow discolouration on the upper side of the leaf corresponding to where the rust spore is located on the underside. Badly infected leaves will drop and younger plants can be severely stunted or die.

Plants Attacked
A wide variety including: roses, daylilies, frangipani, myrtles, snapdragons, geraniums, orchids

Organic Control Methods for Rust

  • eco-fungicide and eco-rose are registered to control rust in geraniums. Both will destroy the fungal growth quickly and leave a protective coating to prevent new spores germinating. Additional trial work is being done for rust in other plants.
  • Adding eco-seaweed into the mix is also recommended to help plants strengthen their foliage and reduce stress.
  • Remove badly infected leaves and clean up any that are on the ground.
  • Avoid watering the foliage and ensure good airflow around the plant.

Myrtle Rust
This is a new rust which attacks plants in the myrtle family (eg eucalypts, lilly pilly and melaleucas). eco-fungicide and eco-rose are not officially registered for controlling this disease so you won’t see it on their labels. They are however broad spectrum fungicides and we have had several reports from the field that users were happy with the results against Myrtle Rust. Further research is being undertaken.

Currently eco-fungicide has approval for Myrtle Rust suppression on tea trees (APVMA PERMIT NUMBER – PER13793).

Rust on geranium leaves

Rust spores on geranium leaf

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