How to Grow Roses

Guide Note

Roses have been grown in gardens for hundreds of years. If you want to add a few bushes to your garden, here is the guide on how to do it.

Table of Contents

• Introduction
• Step 1: Different Types of Roses
• Step 2: Planting Roses
• Step 3: Fertilizing Roses
• Step 4: Watering Roses
• Step 5: Pruning and Cutting Roses
• Step 6: Dealing with Pests
• Step 7: Dealing with Disease
• Step 8: Winter Care for Roses
• Conclusion
• Resources

Growing Roses Tips

1. Plant roses in full sun.
2. Water roses in the morning.
3. Ladybugs can be your rose's best friend.
4. Prune roses in the spring.
5. Make sure you protect your roses in the winter.

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Introduction

• Bette Midler sang about it. William Shakespeare, Gertrude Stein and Robert Burns wrote about it. It is the national flower of both the United States and Great Britain. It is the rose, and it is a favorite of many gardeners around the world. If you want it to become a part of your garden, then here is a basic guide on how to plant and grow roses.

Step 1: Understanding the Different Types of Roses

• Roses can be classified in a variety of ways including by growth habit, lineage and flowering characteristics. Rather than go into the thousands of different types of roses, a general overview of the different classifications is given.

1. 

   These picturesque blossoms come in many different varieties. (Creative Commons photo by Audrey)
   Bush roses: Self-supporting and grow upright. They can range from 6 inches to 6 feet in height.
2. Climbing roses: Produce long, vigorous canes that need support and may grow over 20 feet in length.
3. Ground covers: Low growing varieties that can reach 2 1/2 feet in height.¹
4. Modern roses: One of the three main groupings of roses.² It includes all classes of roses that were in existence after 1867 including all miniature, hybrid tea, shrub, floribunda, grandiflora as well as all climbing varieties of these types.
5. Mounding shrub: Roses that are more rambling than upright varieties.¹
6. Old garden roses: One of the three main groupings of roses.² It includes all classes of roses that were in existence before 1867 including all tea and climbing tea varieties.
7. Species roses: One of the three main groupings of roses.² These are from the genus Rosa and are found growing naturally throughout the Northern Hemisphere.³ Species roses often have single blossoms that bloom once a year, are very hardy and disease resistant.
8. Upright plants: Medium to large shrub roses with uniform foliage and bloom.¹

• For more information about the different varieties of roses, check out any of the following links:
  1. All-America Rose Selections: Types of Roses
  2. Clemson Extension: Growing Roses
  3. University of Illinois Extension: Different Kinds of Roses
  4. American Rose Society: English and Other Shrub Roses | Old Garden Roses and Older Roses | About Miniature and Mini-flora Roses

Step 2: Planting Roses

1. 

   Give your plants ample space to soak up plenty of sun. (Creative Commons photo by Jon Bragg)
   Roses should be planted in the fall or early spring while they are still dormant.⁴
2. Choose a location that receives at least 6 hours of direct sunlight every day.⁵
3. Spots that receive morning sunlight are preferable to sites that receive afternoon sunshine.⁴
4. Make sure the site allows for good air circulation.⁶
5. Soil should be well draining.⁶
6. Roses prefer a soil with a pH level between 5.5 and 7.0.⁶
7. Plant spacing varies according to the variety. Here is a basic guideline of how roses should be spaced:
   1. Hybrid teas, floribundas & grandifloras: 18 to 30 inches
   2. Shrub Roses: their mature height
   3. Climbers (on fences): 8 to 12 feet
   4. Climbers (on walls): 3 feet
   5. Miniatures: 12 to 15 inches⁶

Preparing the Soil Before Planting

1. Dig a hole that is wide enough and deep enough to fit the roots of the plant.
2. Add fertilizer and lime according to soil test recommendations.⁷
3. Most soils will benefit the addition of organic matter, such as compost, rotted manure, leaf mold, peat moss, composted sewage sludge, fine grain potting bark or similar material. Turn the organic matter into the soil with a shovel or garden spade to a depth of 1 foot.⁶

Planting Bare Root Roses

1. Remove wrappings.⁷
2. Place roots into a bucket of warm water for at least 8 hours but no more than up to 24 hours.^{8 7}
3. Prune off any damaged or diseased stems and roots.⁵
4. Remaining roots should be pruned until they are between 8 to 10 inches long.⁵ You want to remove about one-third of the root system, which will stimulate new root growth.⁷
5. Prune canes to remove any thin or weak growth. Try to keep about three to five canes per plant with each cane having three to five buds. Remove any canes that are thinner than a pencil.⁸
6. Prune the tops of hybrid teas, floribundas, grandifloras, and climbers back to 12 to 15 inches.⁷
7. Create a cone-shaped mound of soil in the center of your hole and spread the roots around it.⁵
8. Place the plant so that the bud union is at soil level.⁵
9. Add soil until the hole is two-thirds full.
10. Water thoroughly to allow the soil to settle between the roots. Do not tamp the soil.⁸
11. Once the water has drained away, add more soil and repeat until the soil in the hole reaches the original level.⁸
12. Build another soil mound around the bush to cover two thirds of the canes until new growth is approximately 1 to 2 inches long.⁵

Planting Potted Roses

1. Tip the pot on its side and gently tap the root ball out.⁸
2. Prune canes to remove any weak, diseased or broken canes.⁵
3. Dig a hole at least 8 inches wider than the root ball and deep enough to plant the rose at the proper depth. You want to plant the rose so the soil reaches the graft union or slightly below the soil line. (graft union at or slightly below the soil line).⁵
4. Place soil in the hole around the soil ball.
5. Water thoroughly.⁷
6. Do not tamp in the soil after watering.⁷

Step 3: Fertilizing Roses

• Fertilizing should be done on a regular basis. How much and how often will depend on various factors. Some will recommend fertilizing once a month, others only three times a year.^{9 10} Therefore, you should test your soil before applying any fertilizer.⁷

1. Soils around existing rose bushes usually lack nitrogen and potassium.⁷
2. Using a higher nitrogen fertilizer at the beginning of the season will promote leaves and roots to grow.¹¹
3. Phosphorus helps promote flowers to bloom.¹¹ Use a fertilizer that is higher in phosphorus once buds begin to appear.¹¹
4. Roses are susceptible to iron chlorosis. This will cause leaves to turn a light-yellow color while the stems remain a dark green. It can be treated by spraying iron chelate onto the leaves.¹² However, since alkaline soil tends to make iron and manganese less available to plants, incorporating powdered sulfur into the soil will help make the soil more acidic.^{13 12}
5. Various spring and fall tonics can be applied to your rose bushes. Recipes for some of them can be founded at these sites:
   1. Rose Magazine: Spring and Fall Rose Tonic
   2. Spring Valley Roses: How to Grow Roses
   3. American Rose Society: Fertilizers: When and How
6. Although general-purpose fertilizers as well as rose-specific fertilizers exist, some gardeners choose to use other ingredients.¹⁴ These things include:
   1. Manure.¹⁵
   2. Alfalfa or alfalfa tea.^{16 17}
   3. Epsom salts.⁹
   4. Bone Meal or rock phosphate.⁹
   5. Fish or kelp liquid fertilizer.⁹

Step 4: Watering Roses

• Roses love water and needs at least one-inch of water each week during the growing season.¹⁰ However, this amount can change depending on different factors. A mature rose bush can lose as much as 5 gallons of water in one day during hot or dry weather.¹⁸

1. 

   Keep thirsty blossoms well-hydrated. (Creative Commons photo by Mrs. Gemstone)
   Consistent moisture is essential. Do not allow the soil to dry out between waterings.⁹
2. Soak the soil using a slow-moving stream of water around the base of the plant until it reaches a depth of 8 to 10 inches.⁷
3. Water in the morning to ensure that leaves dry quickly.⁷
4. Water at the base of the plant to avoid wetting the leaves.¹¹
5. Roses should not be standing in water because it will rot the roots.⁹
6. Roses will wilt, drop leaves, grow smaller leaves or stop bloom production when they are not receiving enough water.¹⁸
7. Signs of too much water include limp and yellow leaves and leaves that fall off the bottom of the bush prematurely.¹⁸
8. Water clay soils less often than loam soils and loam soils less often than sandy soils.¹⁹

Step 5: Pruning and Cutting Roses

• Pruning should be done in the spring after the danger of frost has passed because it will improve the size, quality and color of your roses.⁷ Before pruning, make sure you have a pair of sharp pruning shears and some heavy gardening gloves.

1. Make all cuts about 1/4 inch above a bud that is facing the outside.²⁰
2. Cut at a 45 to 50° angle.⁵
3. First, prune any dead, damaged or weak growth.⁷
4. Next, prune any canes that cross over and rub against each other.²¹
5. Always remove older canes before removing newer canes.²¹
6. Seal your cuts with a drop of carpenter's glue, nail polish or black pruning sealer to ensure a quicker recovery.²⁰
7. When you are finished, you should have removed about one-third to one-half of the volume of the plant and your rose bush should have only healthy canes with the center of the plant should be open.²²

• For information on how to prune specific varieties of roses, check out any of the following links:
  1. Ed Hume Seeds: March is Rose Pruning Time
  2. Alabama Cooperative Extension System: Growing Roses
  3. Kansas State University: Growing Roses  
  4. Clemson Extension: Pruning Roses
  5. Adams County Cooperative Extension: Pruning Roses
  6. University of Illinois Extension: Pruning Roses

• YouTube: How to Prune Roses with Rich Baer (Time: 6:38)

Step 6: Dealing with Pests

• Insects can be a problem with roses. Although they do not spread viruses and disease as they do on other plants, they can still leave you with damaged blooms and sickly rose bushes. Here are some of the more common pests.

Aphids

• Aphids are the most common pests on roses.²³ They are soft-bodied insects about 1/8-inch long that vary in color from red, green, yellow or black. Aphid species vary from state to state but include the rose aphid, Macrosiphum rosae, the potato aphid, Macrosiphum euphorbiae, and the cotton aphid, Aphis gossypii.
  1. 

     Stay watchful lest your plants become infested with aphids. (Creative Commons photo by aroid)
     Aphids damage roses by sucking out the sap from their stems and buds, which can cause curling, yellowing, and distortion of leaves and stunting of shoots.²⁴
  2. They also produce a fluid called "honeydew" which may develop a sooty mold fungus.²⁵

• Early detection is essential when trying to control aphids.²⁵ Check your roses at least twice a week.
  1. Aphids have many natural enemies including ladybugs (lady beetles), soldier beetles and syrphid flies.
  2. Because ants feed on the honeydew excreted by aphids, they will protect them against enemies. Control ants using sticky barriers, baits, or traps.²⁶
  3. Insecticides that contain bifenthrin, carbaryl, cyfluthrin, esfenvalerate, horticultural oil, insecticidal soap, lambda cyhalothrin, malathion, neem oil, permethrin, or pyrethrin will kill aphids.²⁷
  4. You can also use soil drenches or granular applications of imidacloprid, dinotefuran, or disulfoton See Table 1 for products containing these insecticides.²⁷
  5. Spraying plants with a mixture that is 1 part Listerine and 1 part water has been known to make plants unpalatable to aphids.²⁸

Japanese Beetles

• Japanese beetles (Popillia japonica) is 1/2-inch long metallic green and copper brown beetles that feed on flowers, buds and leaves of roses.
  1. Grubs live in the soil and feed on grass roots.²⁹
  2. Adults feed from late June to early October.²⁹

• Controlling Japanese beetles can be done through various chemical and non-chemical methods.
  1. Many gardeners feel that Sevin provides the best control.²³
  2. Beetle traps are not recommended because they simply attract more beetles to the roses.³⁰
  3. An effective method of getting rid of Japanese beetles is to treat the surrounding grassy areas with Milky Spore.³⁰ It contains a bacterium that causes a disease in grubs.
  4. Other insecticides that will work on Japanese beetles include bifenthrin, carbaryl, cyfluthrin, esfenvalerate, lambda cyhalothrin, malathion, neem oil, permethrin and pyrethrin.²⁷
  5. Soil drenches or granular applications of imidacloprid, dinotefuran, or disulfoton are better because they last longer.²⁷

Thrips

• Thrips are extremely small insects that range in color from translucent, yellowish-white, brown or black and are usually found inside blossoms. Not all thrips are necessarily bad since Western flower thrips (Frankliniella occidentalis) are a natural predator of spider mites.²⁶
  1. Thrips cause brown streaks on blossom petals or cause petals to become distorted.²⁶
  2. They can also feed on the upper surface of leaves.²⁸
  3. Fragrant, light-colored roses are attacked more often and damaged more severely.²⁶
  4. Cultivars with sepals that remain tightly wrapped until it blooms have less problems with thrips.³¹
  5. Thrips are worse when temperatures are warm during late June, July and August. ²³

• Controlling thrips can be difficult since insecticides are most effective when thrips are still developing and hidden deep within buds and flowers.²⁶
  1. Remove spent blooms from bushes promptly and destroy them (along with any thrips inside).³²
  2. Regularly water your roses.²⁸
  3. Acephate, bifenthrin, cyfluthrin, esfenvalerate, lambda cyhalothrin, permethrin and spinosad are insecticides that are known to kill thrips.²⁷
  4. Soil drenches or granular applications of dinotefuran, disulfoton or imidacloprid can also help control thrips.²⁷

Spider Mites

• Spider mites are extremely small relatives of spiders. To the naked eye, they look tiny red, brown or black specks.³³ They suck the sap out of leaves, leaving them yellowed, dried, and curled up before they fall off.²³
  1. Leaves may appear dull and the underside will feel rough.³⁴
  2. Webbing can appear on the underside of leaves, which is the sign of a heavy infestation.^{34 23}
  3. Spider mites are most problematic during hot, dry weather.²⁸

• Chemicals can be used to control spider mites, but must be done cautiously. Mites can easily become resistant.
  1. Spray insecticidal soap, horticultural oil, or neem oil can be sprayed on the underside of the leaves to kill mites.²⁶
  2. Do not use a broad-spectrum insecticide such as carbaryl.²⁶ It will kill off the natural enemies of spider mites and actually make the infestation worse.
  3. You can try applying rubbing alcohol to the affected leaves.²⁸
  4. You can also use a garden hose to spray the underside of the leaves every two to three days to manage mites. This will interrupt their life cycle.²³

Scale

• Scales that will attack roses include armored scales such as the California red scale (Aonidiella aurantii), the rose scale (Aulacaspis rosae), the latania scale (Hemiberlesia lataniae) and the San Jose scale (Quadraspidiotus perniciosus). They also include soft scales such as the frosted scale (Parthenolecanium pruinosum), the Kuno scale (Eulecanium kunoense) and cotton cushion scale (Icerya purchasi).
  1. Scale insects form tiny crust-like formations that are either gray, white or tan on the stems of roses.²⁸
  2. Leaves may also have a sticky honeydew substance on them when they have soft scales on them.²⁸

• Controlling scales can be using natural enemies, pruning, and using horticultural oils or insecticidal sprays.
  1. Natural enemies of scales include ladybugs, lacewings, mites and parasitic wasps.³⁵
  2. If the infestation is light, you can try scraping off scales by hand and destroying them.²⁷
  3. Prune and destroy heavily infested canes.³⁵
  4. Horticultural oils can be applied at a rate of 3 to 4 percent during the dormant season and 1 to 2 percent during the spring to control scales. Spray when the temperature is between 40 to 85°F.²⁷
  5. Insecticidal sprays that are effective against young scales (known as crawlers) include: acephate, bifenthrin, cyfluthrin, esfenvalerate, lambda cyhalothrin, malathion, or permethrin.²⁷

Rose Leafhopper

• Rose leafhoppers are 1/4- to 1/2-inch long, wedge-shaped insects that vary in color from white, gray, yellow or green.²⁷
  1. Adults lay eggs within rose canes in the fall and hatch in the spring. The resulting wounds can lead to stem canker and other fungal diseases.²⁷
  2. Both adults and nymphs feed on the undersides of leaves which causes white stippling and spots.
     1. The stippling is larger than mite stippling.²⁶
     2. Damaged leaves may drop prematurely.²⁷
  3. You may also notice cast skins and the absence of webbing on the underside of leaves.²⁶

• Because they can be very difficult to control and rarely do any serious harm, most control methods are generally not recommended.³⁶
  1. If population gets too bad, you can apply insecticidal soap or narrow-range oil.³⁶
  2. Make sure to spray lower leaf surfaces thoroughly.
  3. Insecticidal sprays that are effective against rose leafhoppers include: acephate, bifenthrin, cyfluthrin, esfenvalerate, lambda cyhalothrin, malathion and permethrin.²⁷
  4. You can also use soil drenches or granular applications of dinotefuran, disulfoton or imidacloprid to suppress leafhopper populations.²⁷
  5. Avoid using broad spectrum insecticides that will kill the natural enemies of rose leafhoppers such as damsel bugs and assassin bugs.²⁷

Rose Slugs or Sawfly Larvae

• There are three types of slugs that can cause problems on roses—all are actually the larvae of sawflies.
  1. The roseslug, Endelomyia aethiops, is black to pale green with legs.²⁶
  2. The bristly roseslug, Cladius difformis, is pale green with hairlike bristles over its body. It will grow between 3/8- to 5/8-inch long.³⁷
  3. The curled roseslug, Allantus cinctus, is pastel green with white spots on its thorax and abdomen and a yellowish head with black eye spots. It will grow about 3/4-inch long.³⁷

• Depending on the species, rose slugs will feed on either the upper or lower surface of the leaves between the veins and may chew large holes into the leaf.²⁷
  1. Rose slugs can removed using your fingers or with a strong stream of water. Once removed, they cannot climb back onto the leaves.²⁷
  2. Bacillus thuringiensis will not work because rose slugs are not the larvae of moths or butterflies.³⁷
  3. You can kill rose slugs with an application of insecticidal soap or horticultural oil.^{26 27}
     1. Insecticidal sprays that can be used include acephate, bifenthrin, carbaryl, cyfluthrin, esfenvalerate, lambda cyhalothrin, permethrin or spinosad.²⁷
     2. Spray both the upper and lower leaf surfaces and the soil under the rose bushes where the larvae pupate prior to overwintering.³⁷

Other Insects

• Caterpillars: Caterpillars, which are the larvae of moths and butterflies, are occasionally seen feeding on the leaves of roses.
  1. They will leave irregular-shaped holes on leaves.²⁷
  2. Damage is rarely severe enough to warrant treatment.²⁶
  3. You can either remove the caterpillars by hand or use insecticidal sprays such as Bacillus thuringiensis, acephate, bifenthrin, carbaryl, cyfluthrin, esfenvalerate, lambda cyhalothrin, malathion, neem oil, permethrin, pyrethrin or spinosad.
  4. Soil drenches or granular applications of imidacloprid, dinotefuran, or disulfoton will also work.²⁷

Certain species of bees harm, rather than help, your roses. (Creative Commons photo by Audrey)

• Leafcutting or Leaf Cutter Bees: Leafcutting bees, also known as leaf cutter bees, are part of the Megachile species.³⁸
  1. They appear similar to honeybees, but have a metallic purple or green color and are about 1/2-inch long.
  2. Females cut round sections out of the edges of leaves to line their nest.²³
  3. Because bees are important for pollination and they are not harming the plant, they should be tolerated rather than killed.²⁸

• Nematodes: Nematodes are microscopic, eel-like roundworms that live and feed on plant roots.³⁹
  1. They can cause low plant vigor, small yellow leaves, stunting, fewer bud formations and leaves to shed early.⁴⁰
  2. There are no chemicals available on the market that will control nematodes.⁷

• Rose Midges: Rose midges (Dasineura rhodophaga) are very tiny flies that lay eggs inside the sepals of flower buds.
  1. When eggs hatch, the larvae feed on the flower buds, causing them to wither, blacken and die.²⁶
  2. The rose midge has no known predators and no natural means of control.²⁸
  3. Don't confuse the rose midge with another midge, Aphidoletes aphidimyza, that feeds on aphid colonies.²⁶

• Rose Galls: Rose gall is caused by a species of wasp that secretes a chemical and causes a round mass on rose canes in which it can lay its eggs.²⁸ Pruning off affected canes should provide sufficient control.²⁶

Step 7: Dealing with Disease

• Dealing with disease is one of the most common problems that rose growers have to deal with. As with any problem, prevention is always better than treatment. Below you will find how to do both with some of the major diseases that affect roses.

Black Spot

• Black spot (or blackspot) is a very common problem among roses caused by the fungus Diplocarpon rosae.
• Symptoms: Small, round or irregular black spots that ranging in size from 1/16-inch to 1/2-inch in diameter. Canes may develop raised, reddish-purple spots.⁴⁸
  1. Spots will have feathery margins and there will be no powdery growth on the undersides of the leaves.⁴⁹
  2. The spots will be mostly on the upper surface of leaves and will yellow around the spots.⁵⁰
  3. Leaves eventually turn yellow and fall off prematurely.⁴⁸
  4. Unlike other leaf spot disease, black spot has fringed margins and darker, blacker spots.⁴⁸
• Causes: Fungus needs a wet environment of about 85 percent humidity with a temperature of at least 75°F.⁵¹ If these conditions continue for over seven hours, the fungus will germinate and symptoms will appear with three to ten days.⁵²
  1. It can be spread by splashing water as well as on clothing, tools and your hands.^{53 54}
  2. Miniature roses are more susceptible than other varieties of roses.⁴⁹
  3. The fungus can overwinter on fallen leaves and stem cankers.⁵³
• Treatment: Treatment for blackspot includes pruning and using fungicides.
  1. Neem oil (Triact), propiconazole (Banner Maxx), stylet oil (JMS Stylet Oil) thiophanane methyl (Cleary 3336 or FungoFlo), chlorothalonil (Daconil 2787), mancozeb (Fore, Dithane or Maneb), thiophanate methyl + mancozeb (Zyban), trifloxystrobin (Compass) and myclobutanil (Systhane) are fungicides that have been approved for treatment of black spot.^{51 48}
  2. Spray a mixture of 4 teaspoons baking soda in a gallon of water and a 1 percent solution of narrow-range horticultural oil or Neem oil.⁴⁹ Do not spray on blossoms.
  3. Remove infected canes by pruning them back to within 1 to 2 inches of the bud union in the fall or early spring.⁵⁵
  4. Remove infected leaves when they appear.⁵⁵
  5. One home remedy that may work is to use a solution of 1 teaspoon baking soda, 1 quart of water and a few drops of liquid soap.⁵² Spray infected plants thoroughly.
• Prevention: Taking steps to prevent black spot is advisable since it is such a wide-spread problem.
  1. Plant varieties of roses with a higher resistance to black spot.⁵³ You can find lists of varieties that are resistant:
     1. Ohio State University Extension Fact Sheet: Black Spot of Roses
     2. Purdue University: Reduce Defoliation From Rose Black Spot; Plant Tolerant Cultivars (March 22, 2004)
     3. Virginia Cooperative Extension: Rose Black Spot
     4. Berkeley Horticultural Nursery: Disease Resistant Roses
  2. Do not wet the leaves when watering.⁵³
  3. Water in the morning so the leaves have a chance to dry.⁴⁹
  4. Plant roses in an area with good air circulation.⁵³
  5. Spraying a fungicide such as triforine, chlorothalonil or phaltan may help prevent it.^{49 50} Spray after it has rained.⁵²
  6. Do not used infected plants in compost.⁵²

Powdery Mildew

• Powdery Mildew is caused by the fungus Sphaerotheca pannosa var. rosae and is a widespread and serious problem with roses.⁵⁵

• 

  Powdery mildew affects many kinds of plants, including roses. (Creative Commons photo by Jeff Kubina)
  Symptoms: White to gray fuzzy powdery growth on both surfaces of the leaves, shoots, sepals, buds, and petals.⁵⁶
  1. Young, expanding leaves and shoots may twist and distort or develop a purple coloration.^{40 53}
  2. Mature leaves are less likely to be affected.⁵³
  3. Mildew will affect the top of the plant first.⁵³
  4. Flower buds may fail to open or produce poor-quality flowers.⁵⁵
• Causes: Powdery mildew occurs when temperatures are between 70 to 80 degrees F and the humidity is high at night but low during the day.⁵⁵
  1. Worse in shady areas and during cooler periods.⁵⁵
  2. Most severe during dry climatic conditions.⁵⁷
  3. Mildew is spread by wind.⁵⁷
  4. It is rarely seen during hot weather.⁴⁰
• Treatment: Once powdery mildew is visible, it can't be eradicated.⁵⁸ However, there are some things you can do to limit its effects.
  1. Prune diseased leaves and canes during the growing season.⁵⁶
  2. Azoxystrobin (Heritage), Fenarimol (Rubigan), lime sulfur, Myclobutanil (Systhane), neem oil (Triact), Piperalin (Pipron), potassium bicarbonate (Kaligreen), Stylet oil (JMS Stylet Oil), Triadimefon (Strike), wettable sulfur copper hydroxide, copper salts of fatty acids, copper sulfate pentahydrate, propiconazole, thiophanate-methyl, triadimefon, triforine or triforine + acephate & hexakis are fungicides that have been approved for treatment of powdery mildew.^{51 55}
• Prevention: Preventative methods are essential when dealing with powdery mildew and must be done on a regular basis.⁵⁸
  1. Protect new growth with a cover of fungicide.⁵³
  2. Plant roses in sunny areas with good air circulation.⁵⁹
  3. Sodium bicarbonate (baking soda) when combined with horticultural oils can control powdery mildew. Use 4 teaspoons of baking soda per gallon of water and a 1 perscent solution of narrow range oil.⁵⁶ Apply early in the morning.⁵⁹
  4. Control measures may not be needed until the drier months of late summer.⁵⁵
  5. Planting varieties of roses with a resistance to powdery mildew is also a good idea. You can find lists of varieties that are resistant:
     1. Purdue University: Reduce Defoliation From Rose Black Spot; Plant Tolerant Cultivars (March 22, 2004)
     2. Virginia Cooperative Extension: Powdery Mildew-Resistant Woody Ornamentals
     3. Berkeley Horticultural Nursery: Disease Resistant Roses
     4. Alabama Cooperative Extension System: Diseases of Roses and Their Control

Downy Mildew

• Downy mildew is a fairly common problem on roses that is caused by the fungus Peronospora sparsa.⁶⁰

• Symptoms: Downy mildew causes purple, red or dark brown spots about 1/2-inch in diameter on the leaves.
  1. The undersides of leaves may be covered with gray downy fungal growth.⁴⁰
  2. Spots may be surrounded by a yellow halo.⁴⁰
  3. Leaves may yellow and drop within two days of infection.⁵¹
  4. Symptoms will appear on the top third of the plant and move their way down the plant.⁵¹
• Causes: It is most common when temperatures are below 80°F and humidity is above 85 percent.⁶⁰ It can be spread by splashing water and through the air.⁵¹

• Treatment: Because it is often mistaken for blackspot, it is important that you have accurately diagnosed the problem before beginning a treatment.⁶⁰
  1. Neem oil (Triact), dithiocarbamates (Dithane T&ampO and Protect), sulfur dusts azoxystrobin (Heritage 50W) and fosethyl-Al (Aliette T/O or Prodigy T/O) have been approved for the control of downy mildew.^{51 61 40}
  2. You should also remove and destroy any diseased canes and leaves.⁴⁰
• Prevention: The best way to avoid problems with fungus is to plant roses in areas with full sun.⁴⁰
  1. Prune plants to increase air circulation.⁶²
  2. Avoid overhead watering.⁶³

Stem Canker and Dieback

• Canker is a disease caused by a combination of stress and a type of fungi including Botryosphaeria, Leptosphaeria, Coniothyrium or Cryptosporella.^{53 55}

• Symptoms: Cankers usually appear as brown, oval-shaped, sunken, or shriveled areas, but may look different depending on the type of fungi infecting the roses.⁵³

• Causes: Canes are infected through wounds during periods of humid weather.⁴⁰ It is common on canes weakened by black spot, poor nutrition or winter injury.⁵⁵

• Treatment: Prune and destroy any infected canes.⁶⁴ Make sure you disinfect your pruning shears in alcohol after each cut. Fungicides used to treat black spot and powdery mildew can help control stem canker.⁴⁰

• Prevention: Preventing injury to your rose bushes during the winter, when pruning or flower cutting, and during cultivating and transplanting is the best way to avoid stem cankers.⁵⁵ Also make sure you prune your rose bushes properly.

Botrytis Blight

• Botryris blight is caused by the fungus Botrytis cinerea that attacks dying tissue on rose bushes. It is also called gray mold.⁵³

• Symptoms: First symptoms appear as small light-colored spots that are sometimes surrounded by a reddish-maroon halo that can expand into large, gray-brown, irregular blotches that cover much of the petal.⁵¹
  1. Infected buds fail to open and may droop.⁵¹ This is similar to symptoms caused by thrips.^{51 55}
  2. Infected canes have discolored sunken areas and will dieback.⁵⁵
  3. More frequently found on older parts of the rose bush.⁵³

• Causes: More common during cool and rainy weather during the spring or summer when the temperature is between 62 to 72°F.^{65 55}
  1. Spread through air currants.⁵¹
  2. Develops more often on canes that have been damaged or are kept too wet.⁵⁵

• Treatment: Fungicides that control black spot, such as chlorothalonil (Daconil), myclobutanil (Immunox) and thiophanane methyl (Cleary's 3336), captan and neem oil (clarified hydrophobic extract) have been effective against Botrytis blight.^{40 55}
  1. Other fungicides that can work include fenhexamide (Decree), fixed copper (Kocide, BlueShield, Champ), mancozeb (Dithane) and neem oil have been approved for treatment of Botrytis spp.⁵¹
  2. Use PCNB or copper sulfate pentahydrate on dormant bushes.⁵⁵
  3. Prune out infected blooms, canes and buds immediately.⁴⁰

• Prevention: Preventing Botrytis blight is done though good sanitation practices and reducing humidity.⁶⁶
  1. Prune the bush to improve air circulation.⁶⁷
  2. Avoid overhead watering or wetting the leaves when watering.⁶⁷
  3. Remove and dispose of any fading flowers, fallen leaves and debris around roses.⁵⁵

Rust

• Rust is a disease caused by several species of species of the fungus Phragmidium that is more prevalent on the West Coast than the East Coast.⁶⁸

• Symptoms: Small, orange, powdery pustules appear on parts of the plant starting on the underside of lower leaves.⁶⁹
  1. Upper sides of leaves may discolor and the leaves turn yellow may drop.⁶⁶
  2. In the late summer or early fall, it can appear as masses of dark brown or black spores on the leaves and stems.⁶⁹
• Causes: Rust can develop when the temperature is between 65 to 70 degrees with continuous moisture for over two hours.⁷⁰ Rain and wind will spread spores.⁶⁸

• Treatment: Remove and destroy any affected leaves.⁶⁸ If necessary, treat with a fungicide. Azoxystrobin (Heritage), mancozeb (Dithane), myclobutanil (Systhane), propiconazole (Banner Maxx) and triadimefon (Strike) ferbam, and lime sulfur are fungicides that have been approved for treatment of rusts.^{51 55}

• Prevention: With nine different varieties of rust that can infect roses, prevention can be difficult.
  1. Plant varieties of roses with a resistance to rust. To find lists of rose varieties that are resistant to rust check out:
     1. Purdue University: Reduce Defoliation from Rose Black Spot; Plant Tolerant Cultivars (March 22, 2004)
     2. Berkeley Horticultural Nursery: Disease Resistant Roses
     3. University of Illinois Extension: Common Rust of Roses  
     4. Colorado State University Extension: Diseases of Roses in Colorado
  2. Destroy any wild or uncared-for roses that are nearby.
  3. Make sure there is good air circulation around the plants.⁶⁹
  4. Water before noon and make sure the leaves do not get wet.⁵⁵
  5. Use fungicides as a preventative.⁶⁶

Viruses

• Rose mosaic virus and rose leaf curl virus are the two major viruses that infect roses.

• Symptoms: Symptoms of viruses vary. Rose mosaic virus may cause yellow wavy line patterns and ring spots, erratic white to yellow line patterns, yellow-green mottle on leaves, and vein clearing.^{55 40} Rose leaf curl virus will cause leaves to yellow, curl downward and eventually die.⁶⁶

• Causes: Rose viruses are only transmitted when infected buds, scions or rootstock are grafted onto healthy plants.