Rust spots on roses

Treating Common Rose Disease

The three most common rose diseases are powdery mildew, rust and black spot. Rose diseases are best prevented by providing a favorable cultural environment for the roses. Shade and moderate temperatures favor most rose diseases, so locate plants in sunny areas as much as possible and plant the bushes at least four feet apart to provide good air circulation. Avoid high Nitrogen fertilizers. A dormant spray of six tablespoons of Master Nursery® Year Round Spray Oil (Horticultural Oil) mixed with two tablespoons of Monterey Liqui-Cop® per gallon of water applied immediately after pruning will help prevent early appearance of these diseases. One tablespoon of Monterey Liqui-Cop® mixed with four tablespoons of the Master Nursery® Year Round Spray Oil in one gallon of water, applied monthly, will act as a preventive and eradicant for these diseases. Be sure to check instructions on the containers. Never apply Horticultural Oil (or any oil spray) to water stressed plants or when the temperatures will be 85˚F or greater. Likewise, do not spray plants with oil spray or with sulfur within one month of each other.

Fungicides fall into two broad categories; preventives and eradicants. Most rose fungicides are preventive and must be applied before the plant becomes infected and will prevent new infections from occurring. An eradicant can kill an existing infection.

Powdery mildew is the most common fungus disease of roses. It appears as a white to gray powder coating upper, leaf surfaces. In severe cases it will also be found on lower leaf surfaces and coating emerging flower buds. Initially, it can be rubbed off between the thumb and fore finger but soon reappears. It can be prevented if Safer® Garden Fungicide or a mixture of Monterey Liqui-Cop® (one tablespoon per gallon of water) and Master Nursery® Year Round Spray Oil (four tablespoons per gallon of water) is sprayed and covers the plant to dripping before the plant shows symptoms of the disease. Copper sprays with less than 25% Copper are of little value. A mixture of Monterey Liqui-Cop® at one tablespoon per gallon, plus Master Nursery® Year Round Spray Oil at five tablespoons per gallon H20 and Bonide® Fung-onil ™ (Chlorothalonil) are used as preventives and eradicants. The spread of powdery mildew will be reduced when the plants receive an overhead water spray. The water washes off the spores from the mildew and when spores land in water, they die. Irrigate in mid-morning so plants dry rapidly and reduce the likelihood of other fungus infections such as black spot or rust.

As part of its Pest Management Program, the UC Department of Agriculture and Natural Resources has stated, “several least-toxic fungicides are available including horticultural oils (Year Round Spray Oil, Neem Oil, Jojoba Oil) sulfur, potassium carbonate and the biological fungicide, Serenade. With the exception of the oils, these materials are primarily preventive. Oils work best as eradicants, but also have some protective activity”.

A black spot appears as circular black spots circled in yellow and only on upper leaf surfaces. The spots may coalesce to form large spots which do not penetrate the leaf. Black spot is spread by splashing water. It becomes less of a problem as our weather becomes warm and dry. Overhead watering is to be avoided except as mentioned above. Badly and moderately infected leaves should be removed and discarded. Do not compost.

Rust initially appears as tiny black spots on the top and bottom of a leaf. As the spots enlarge they become rust colored and finally black. The rust pustule penetrates both upper and lower leaf surfaces until the entire leaf is yellow and drops off. Rust fungus is a midseason disease and can defoliate a plant. Monterey Liqui-Cop® and Safer® Garden Fungicide are effective preventives. Pick off and discard severely infected leaves. Reapply the chemicals as new leaves appear. Master Nursery® Year Round Spray Oil or Neem Oil will also act as an eradicant. Bonide® Fung-onil™ is effective as an eradicant and preventives for mildew, black spot and rust on roses. Be sure to check instructions on the containers.

Stem cankers may appear on the canes of roses. They are indentations parallel to the stem ranging from one-half inch to three or four inches long. They are caused by a fungus and can kill the stem. There is no cure so the treatment is to cut the cane four to six inches below the canker and dispose of it. Do not compost.

Viruses may appear on roses, usually on bushes sold ten or more years ago. Most commonly they appear on new spring foliage, stressed plants or at the end of the growing season. At least two different kinds of viruses could infect roses. One form leaves zig-zag lines that resemble lightning bolts. The other produces yellow circles on the green leaves; these virus symptoms may temporarily disappear when the plant is actively growing. Both viruses may produce a slight stunting of growth but will do no other harm. They are spread by grafting a healthy cutting to a diseased rootstock or a diseased cutting to a healthy rootstock. The virus becomes systemic in the plant and remains there for the life of the plant. There is no cure or remedy.

For further information, see UC ANR Publication 7493: Pest Notes “Powdery Mildew on Ornamentals”.

Make Home Remedies for Pests and Diseases

If you are losing the battle with bugs and disease, try these environmentally friendly alternatives to pesticides. Many problems can be managed with cultural controls before they get out of hand (like pruning off infected leaves or physically removing pests), but sometimes you need more – especially during cool, wet weather.

Natural solutions require more frequent application to achieve control, but do not pose significant health risks like traditional chemicals. As an added benefit, they are generally inexpensive to prepare. Don’t forget to spray the underside of leaves as well as the upper surface during application.

Aphids, Mites, Scale & Whiteflies

Aphids reproduce rapidly and like tender new growth

Spider Mites are found on the undersides of leaves and may cause stippling damage

  • Orange Oil Cleaner – Dilute 1 teaspoon per gallon of water. Use as needed by spraying on leaves. Good coverage is important: Wet leaf surfaces to the point of drip.
  • Soap Spray – Mix ½ teaspoon mild dish soap and 1 teaspoon cooking oil in a 1-quart sprayer filled with water. Spray liberally over entire plant.
  • Bring in Ladybugs – To keep aphids in check, release ladybugs on the affected plant. They will stay as long as there is shelter and host bugs to feed on.
  • Blast with Water – Aphids may also be dislodged by a strong jet of water.

Slugs & Snails

Slug damage on rose leaves

  • Beer – Pour an inch of beer into the bottom of an empty tuna or cat food can. Set it in the garden. Slugs and snails, attracted to the yeast in beer, crawl in and drown.
  • Handpick – Collect at night and remove from the garden area.
  • Coarse Sand, ¼”-minus Gravel, or Hazelnut Shells – Apply sand or gravel in trails around roses, or topdress beds with crushed hazelnut shells. Slugs and snails prefer not to cross abrasive surfaces.

Powdery Mildews, Blackspot & Rusts

Black spot spreads by rain or overhead watering and may cause leaf drop if untreated

  • Baking Soda Spray – Mix 1 tablespoon baking soda and 1 teaspoon cooking oil in 1 gallon of water. Place in spray bottle or tank sprayer and apply liberally. Repeat as needed.
  • Sanitation – Remove infected leaves and destroy. Do not compost. Keep the ground surrounding your roses free of leaf debris and weeds.
  • Cold Water – For Powdery Mildew, spray affected leaves with cold water early in the morning and allow leaves to dry in the sun.

Yellow Leaves

  • Leaves fall when tapped = Too much water.
  • Leaves stay on when tapped = Too dry.
  • Crunchy leaves = Too dry and too late to save. Cut back as needed to promote regrowth.
  • Exceptions: Some rose leaves turn yellow in the fall. This is normal coloration.

Fighting Black Spot on Roses

Fighting black spot effectively in roses involves a three-prong treatment approach. The American Rose Society and the University of California Integrated Pest Management Program note that pesticides containing the active ingredient chlorothalonil are effective components of programs to counteract rose black spot in various stages.3,2 Chlorothalonil-based GardenTech® Daconil® Fungicides fight black spot in roses in three important ways:
1. Prevention
Protecting your roses before they become infected with black spot is the most important step against this disease. This is especially important when you’ve had black spot before or when moist conditions encourage its spread. Start preventive treatments with Daconil® fungicide at what’s known as “bud break,” in early spring. That’s the point when the small buds along rose canes begin to swell and come out of dormancy. By treating every seven to 14 days, or until conditions no longer favor the disease, unfurling new leaves are protected right from the start.
2. Suppression
If black spot is already active on your roses, move quickly to control and stop its advance. Unless you treat with a highly effective product such as Daconil® fungicide, black spot can move through your garden — and it won’t stop at roses. Begin active treatments with Daconil® fungicide at the very first sign of disease to stop black spot and limit its damage. Treat every seven to 14 days or as long as weather conditions warrant, and mark your garden journal to remember to start preventative treatments early next year.
3. Protection
Another important aspect to treating infected roses is protecting healthy tissue from new infection. Even when black spot is active on a rose, there’s hope. Your regular treatments with Daconil® fungicide protect the healthy parts of roses from succumbing to the disease, as it stops and controls disease in infected parts.

Rose Rust Disease – Treating Rust On Roses

By Stan V. Griep
American Rose Society Consulting Master Rosarian – Rocky Mountain District

Rust fungus, caused by Phragmidium fungus, affects roses. There are actually nine species of the rose rust fungus. Roses and rust are a frustrating combination for rose gardeners because this fungus can not only ruin the look of roses, but, if left untreated, rust spots on roses will eventually kill the plant. Let’s learn more about how to treat rose rust.

Symptoms of Rose Rust Disease

Rose rust most commonly appears in spring and fall, but can appear in the summer months as well.

Rose rust fungus appears as small orange or rust colored spots on the leaves and will grow to bigger markings as the infection advances. The spots on the canes of the rose bush are orange or rust colored but become black in the fall and winter.

Rose leaves that are badly infected will fall from the bush. Many rose bushes affected by rose rust will defoliate. Rose rust can also cause the leaves on a rose bush to wilt.

How to Treat Rose Rust

Like powdery mildew and black spot fungi, humidity levels and temperatures create the conditions for rose rust disease to attack rose bushes. Keeping good airflow through and around the rose bushes will help prevent this rose rust disease from developing. Also, disposing of old rose leaves will prevent rose rust fungus from overwintering and re-infecting your roses next year.

If it does attack your rose bushes, spraying them with a fungicide at intervals as directed should take care of the problem. Also, be sure to dispose of any infected leaves, as they can spread the rose rust fungus to other rose bushes.

Now that you know how to treat rose rust, you can help your rose bush get rid of the rose rust disease that is affecting it. Treating rust on roses is relatively simply and you will be rewarded with rose bushes that are once again beautiful and lovely to look at.

Rose Rust

Yellow spots on upper leaf surfaces with corresponding powdery, orange to black spots on lower leaf surfaces are typical of rose

Robyn Roberts, UW-Madison Plant Pathology
Revised: 6/8/2013
Item number: XHT1217

What is rose rust? Rose rust is a common fungal disease found in much of North America (including the continental United States) and Europe. Rose rust affects many varieties of rose, though some varieties (e.g., hybrids) are more prone to the disease. Rose rust has been a perennial problem along the Pacific Coast of the United States where mild temperatures and high moisture are favorable for rust development. In the Midwest, extremes in winter and summer temperatures have tended to be less favorable for the disease. However, recent climate changes in the Midwest may lead to rose rust becoming more commonplace in the future.

What does rose rust look like? Rose rust often first appears on lower leaves, but eventually an entire plant can be affected. Typical symptoms include general yellowing of leaves followed by eventual leaf death. Affected rose stems (i.e., canes) can become curled and distorted. As the disease progresses, powdery orange or black, circular spots (called pustules) containing spores of the fungus that causes the disease form on the undersides of leaves, with corresponding yellow spots visible on upper leaf surfaces. Pustules may also form on stems and green flower parts (sepals). Rose rust usually develops in the spring and fall (when favorable mild temperatures and wet conditions are more common), but the disease can affect roses during the summer months as well.

Where does rose rust come from? Rose rust is caused by several species of fungi in the genus Phragmidium. These fungi specifically infect roses. Rose rust is often introduced into a garden on infected shrubs purchased from a nursery or other rose supplier. Once introduced into a garden, rose rust fungi can overwinter in rose leaf debris, as well as on infected rose canes. In the spring, spores produced in debris and on canes can blow to newly emerging rose foliage, leading to new infections.

How do I save a plant with rose rust? Control of rose rust is difficult once symptoms develop. Prune out affected canes and remove leaves as symptoms develop to prevent the spread of rust fungi to other rose shrubs. Destroy these materials by burning (where allowed by local ordinances) or burying them. In the fall, remove and destroy any remaining dead leaves and other rose debris to eliminate places where rose rust fungi can overwinter. If you notice a rust problem very early (before there are many symptoms), fungicide treatments may be useful for managing the disease; however, most fungicides work best when applied before any symptoms appear. If you decide to use fungicides for rust control, select products that are labeled for use on roses and that contains the active ingredients triforine or myclobutanil. Treat every seven to 10 days, and DO NOT use the same active ingredient for all treatments. Instead, alternate use of the two active ingredients listed above to help minimize potential problems with fungicide-resistant strains of rose rust fungi. Be sure to read and follow all label instructions of the fungicides that you select to ensure that you use these products in the safest and most effective manner possible.

How do I avoid problems with rose rust in the future? Whenever possible, plant rose varieties that are less susceptible to rose rust (i.e., avoid hybrid varieties). Always inspect new rose shrubs for rose rust (and other diseases) prior to purchase. DO NOT bring diseased shrubs into your garden. Plant rose shrubs far enough apart so that their foliage does not overlap, and thin your roses on a regular basis. Proper planting and pruning promote good air circulation that will facilitate rapid drying of leaves and canes, thus making the environment less favorable for rust development. Avoid working with your roses when they are wet as you are more likely to spread rust spores under these conditions. Fertilize and water roses appropriately. Well-cared-for plants tend to be less susceptible to disease. When watering, apply water at the base of your shrubs (e.g., with a soaker or drip hose) rather than over the leaves (e.g., with a sprinkler). Watering with a sprinkler tends to spread rust spores and wets leaves and canes, thus providing a more favorable environment for rust infections to occur.

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Tags: disease, rust Categories: Tree & Shrub Problems, Trees & Shrubs

Rose rust

The fungal spores that cause rust are spread on the wind, and they can survive over winter on the soil surface, on fallen debris and even objects such as fences and stakes. The symptoms spread in early summer from patches of orange on the stems and leaf stalks of roses to more obvious orange speckling on the leaves. This can lead to leaf fall. In late summer, look out for black pustules on the leaves. Learn more about rust and hollyhock rust.

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Symptoms

Orange speckling on rose leaves in early summer, sometimes causing the leaves to drop, is followed by black pustules on the leaves in late summer. By autumn it’s almost inevitable that the leaves will drop off.

Find it on

roses

Organic

Promptly prune out any infected stems and destroy them, along with any infected leaves. Grow roses with lots of room around them so the air can circulate, and prune out any congested growth.

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Chemical

Use a preventative copper fungicide in spring before the overwintering spores strike. Make sure you cover all the leaf surfaces.

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