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Roses: Basic Care, Common Diseases and Organic Remedies Advice from a master rosarian on identifying and treating rose diseases From "Dirt On Gardening" episode DDOG-105

Rose growing expert Adena Kalal cares for around 600 rose plants.

A rose by any other name . . . would probably still get aphids. These backyard beauties can be plagued by a number of pests and diseases. If you're looking for alternatives to chemical treatments for rose problems, DIY's The Dirt on Gardening has some answers.

Organic gardening principles utilize more natural methods for growing plants with minimal usage of manmade chemical fertilizers or toxic chemicals. Here are some basic care tips and information on some of the most common rose diseases and organic measures you can take to prevent them.

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Host Kristine Hanson with master rosarian Adena Kalal.

Susceptibility to Disease

As a general rule of thumb, old garden rose varieties tend to be more susceptible to disease. You may want to choose hybrid and newer, more resistant varieties. These have been selectively hybridized and cultivated to be less prone to disease.

Dirt on Gardening Lexicon: A rosarian is a person with expertise or a special interest in the cultivation of roses.

	Figure A
	Figure B

Common Rose Diseases and Organic Treatments

Three of the most common maladies of roses are black spot, powdery mildew and rust. Here are some tips on identification, symptoms and what you can do to help these from becoming serious problems in your rose garden.

Black spot (Diplocarpon rosae) is a well-known fungal disease that occurs in warm, damp conditions, especially when leaves have been wet.

Symptoms:

• Dark brown or black blotches, with irregular margins, appearing on leaves (figures A and B).
  
• Leaves turn yellow and drop off .

• Choose roses that are resistant to black spot. (Get local advice from your nursery or agricultural extension.)
  
• Select a sunny location and properly space plants to promote quick drying of foliage
  
• Avoid overhead watering. Try a drip system instead of a sprinkler
  
• Remove fallen leaves from around the plant and prune any infected canes.
  
• Reduce the spread of spores from fallen leaves by applying a three-inch layer of mulch around the plants.

Figure C

Powdery mildew (Sphaerotheca pannosa var. rosa) develops in cool, wet weather, and appears mostly on new plant growth. It spreads through spores which exist in the air, all the time. Under the right conditions--usually in early spring--it may begin to attack the plant.

Symptoms:

• Powdery white or off-white patches, most commonly seen on leaves but may spread to stems (figure C).
  
• Leaves may drop off.
  
• Buds may fail to open.

• Plant in full sunlight.
  
• Use drip irrigation.
  
• Prune infected canes, and rake and discard affected leaves and flowers during and after the growing season.
  
• The white powder and spores can be washed away using the spray from a hose.
  

  	Figure D
  	Figure E

Symptoms: Early in the season, bright orange pustules on stalks, branches and the underside of leaves (figures D and E). Once the plant has been infested for some time, the orange spots may begin to turn black.

Prevention: Remove infected foliage, stems or even whole plants to protect the healthy ones.

General Tips

To help prevent fungal diseases that thrive under moist conditions, water in the morning rather than the evening. In that way, the leaves will have more time to dry out. Leave sufficient room between plantings so that there's room for air to circulate. Thorough cleanup of wet leaves, especially in winter, will help ensure that spores don't "winter over" and help curb the spread of fungi.

Roses: Organic Treatment Tips

• If you spot a problem on one of your rose plants, don't panic. Learn to live and enjoy your roses with imperfections if you want to grow organically.
  
• Remember that less toxic chemicals and organic products typically help prevent--rather than cure--rose diseases.
  
• There are "environment friendly" organic preparations that you can use for treating some of the common rose diseases. Those include a dilute solution of dish soap in water, baking powder in water solution or horticultural oils. (Horticultural oils are best used when the plant is in the dormant phase, or before the weather gets too hot.)
  
• To be most effective, treatments must begin before symptoms are widespread.
  
• When applying organic treatments, be sure to coat both sides of the leaves.
  
• To decrease the possibility of burning leaves or flowers, water plants the day before you treat them. It's also a good idea to test a few leaves and petals before spraying the whole plant.

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