Question
I have an indoor minature rose which I have noticed has a fine white powder like substance on the leaves, it's almost like talcum powder.

Do you knon what it is and how I can get rid of it?

I have 'washed' the leaves with water which has taken some of it off, but it seems to be re-occuring.

The rose in on my dining room table in a bright spot which does get sunny, I'm not sure if this is the right place to keep it.

I look forward to hearing from you.

Many thanks and kind regards

Answer
Hi Alison,

This is most likely powdery mildew, a fungal infestation.  Powdery mildew is a common problem when there is much humidity in the air.  In garden roses, the branches in the center of the plant are thinned to provide better air circulation and sunlight penetration.  

The same diseases that plague garden roses also plague mini-roses grown indoors.  Roses grown indoors are far more likely to develop diseases and pests because they have been removed from the normal habitat and placed indoors.  

Environment plays a major role in powdery mildew development. Outdoors, the disease occurs during cloudy, humid conditions when days are warm and nights are cool.  These conditions are almost exactly what is found in the common home.

Powdery mildew is common in crowded plantings, in damp areas, or in shaded sites where air movement is restricted.

Mildew can spread rapidly since the disease cycle can be completed in as little as 72 hours. It commonly takes seven to 10 days from the time of infection to the development of symptoms and secondary spore production.

So, to control this disease, you must treat over a 10 day to two week period.

Sodium bicarbonate commonly known as baking soda has been found to posses fungicidal properties. It is recommended for plants that already have powdery mildew to hose down all the infected leaves prior to treatment. This helps to dislodge as many of the spores as possible to help you get better results. Use as a prevention or as treatment at first signs of any of the diseases.

To make: Mix 1 tablespoon baking soda, 2 1/2 tablespoons vegetable oil (canola oil, soybean oil, olive oil, or neem seed oil) with one gallon of water. Shake this up very thoroughly. To this mix add 1/2 teaspoon of pure castille soap and spray. Be sure to agitate your sprayer while you work to keep the ingredients from separating. Cover upper and lower leaf surfaces and spray some on the soil. Repeat every 5-7 days as needed.

Oil sprays that coat and suffocate the fungal pathogen are also effective in protecting roses from powdery mildew-Do not use oil sprays around or near plants that have been treated with sulfur.

Soap sprays such as potassium fatty acids are also an effective alternative to fungicides. Soaps act as a desiccant when applied to the powdery mildew pathogen and are an effective method of protecting roses. Soaps and oils also help to act as a surfactant when tank mixed with a compatible fungicide.


Chemical Control: Several fungicides can be used to control powdery mildew. It is a good idea to alternate between different fungicides during the growing season. This is done to prevent the development of fungicide resistance in the natural powdery mildew population.

I am unsure if any of these chemicals are appropriate for use on indoor plants.  Check with your local garden center for fungicides appropriate for indoor use.  Another option is to take the rose outdoors for the treatment, expose it to a healthier (brighter sunlight, open air, etc.)environment during the treatment.

These so-called miniature roses are perfectly happy outdoors and they will thrive in the summer months if cared for properly.