Powdery mildew disease. Hose off with a hard spray of water, then spray with spray oil, 20% milk solution, sulfur, potassium bicarbonate (Remedy), or a synthetic fungicide labeled for mildew. Many roses are resistant to this disease. If you haven't transplanted the rose, maybe you could return it and get a better kind.

What Michael said -- but avoid using oils if your temperatures are much over 75 deg. (I know most say oils are safe up to 80 or so, but I've burned foliage at 75 deg.)

The diseased leaves will not be made clean, but you can stop progression of the disease.

HOWEVER, I also agree with Michael that it would be wiser to return this rose, if possible, in exchange for one that is not afflicted with mildew.

Jeri

The other fungicides can burn foliage as well during summertime. Be sure the plant is well watered before spraying, and spray in the cool of the morning. Thanks to Jeri for mentioning this risk.

The flocky material can be wiped off of leaves.

I agree with all of the above, however, if this is a brand new rose you just brought home from the nursery chances are it came already infected with the disease. Nurseries are a high pressure area for most common rose fungal diseases. I would treat it now and get it planted out in the fresh air and sunshine and give it a chance to mature before deciding it's an unhealthy plant for your area. Besides, it is possible that it will mature out of it's tendency to mildew. Some roses just need time to mature and build a healthy immune system before they get over this problem. You also do not say where you are at, what zone you're in and what rose it is. All of those things would be helpful to know.

Are you keeping this plant indoors? The photo appears as if it's inside a sun room or some other room with many windows. Don't try this, it won't work. Roses are NOT HOUSEPLANTS. Some minis can be grown under grow lights but it is a royal pain in the nether regions and you won't enjoy the effort and work required for the little rewards obtained. The mildew can easily be a function of too high humidity, too cool temps and restricted air flow with too little direct sun. Even outdoors, the most mildew resistant roses WILL mildew if grown in too little sunlight. Water stress caused by allowing the plant to dry out too far will also force even resistant roses to mildew. Kim

Thanks everybody, today I bought a sulfur based fungicide spray from a store. My other plants also don;t have healthy looking leaves. I am posting the picture, is it also fungal infection.

and one more question, what is spray oil?

Oil for spraying on plants, which can be mineral oil refined for the purpose, neem oil, or jojoba oil. Mineral spray oil could be labeled horticultural oil or summer spray oil. In stronger concentration it is used as a dormant spray.

Yes, that is also powdery mildew on your gerbera daisy. PM can infect many different types of plants. Where ever you are the conditions for PM must be just right at the moment and it's spreading through your garden. Use the fungicide you purchased according to the directions and wait for the weather to change. That should clear things up.

However, there are many species of powdery mildew that are specialized for different groups of plants. Rose PM only affects roses.

I want to emphasize Kim's point--sunlight! Get those plants out in the sun. Powdery mildew is usually associated with too much shade or possibly long periods of overcast, cloudy skies. Sunlight is the solution.

Kate