Looks like a fungus.

[axescot]

This is happening to one of my wife's roses. It's a climbing rose. Looks like a fungus. How can I get rid of it and keep it from coming back?

 

[Sheal]

The problem you have is powdery mildew. Your rose is suffering in a pot, could it be planted in the ground? Roses, particularly climbing roses need space to spread their roots and take in nutrients and water. All roses need to be fed two to three times a year during the growing season and watered well during dry spells. They need good air circulation which helps stop disease and prefer six hours of sunshine a day and three minimum.

 

[axescot]

The problem you have is powdery mildew. Your rose is suffering in a pot, could it be planted in the ground? Roses, particularly climbing roses need space to spread their roots and take in nutrients and water. All roses need to be fed two to three times a year during the growing season and watered well during dry spells. They need good air circulation which helps stop disease and prefer six hours of sunshine a day and three minimum.

@Sheal thanks for the response. If I put it in the ground with sun and food, etc. should I treat the mildew or will it go away on its own?

 

[Sheal]

Yes, the mildew will need to be treated on this occasion but when the rose returns to good health it shouldn't reappear. I'm sorry I can't advise you on the treatment, be it chemical or natural, as I'm not sure what is available to you.

 

[axescot]

Yes, the mildew will need to be treated on this occasion but when the rose returns to good health it shouldn't reappear. I'm sorry I can't advise you on the treatment, be it chemical or natural, as I'm not sure what is available to you.

I have a copper fungicide, neem oil, and soft soap. The article I'm reading also says I should cut the infected leaves.

 

[DirtMechanic]

Powdery mildew is pretty easy. Fungi generally hate acids. Thats why salicylic acid or even aspirin (acetasalicylic acid) can take it out. Also things like oils prevent the fungi enzymes from working on plant tissue chemically and breaking into the cell walls. The copper can build up over years in soil so is getting phased out in some countries. Soap is usually alkaline so the other pH extreme but also works to strip protective coatings away. Like in the fat oils that protected corona virus. The hard thing is keeping something on the roses. I started using cleary's 3336 because of blackspot and it is systemic. Agri-fos works for me in the garden and is considered organic (Potassium salts of phosphonic acid). I like the systemic nature of it. Potassium based remedies may be the better thing for the soil than copper. Potassium is a metal too, in this agri-fos case being absorbed easily by plants and mobile inside them. Plus it is cheap, like me!

 

[Sheal]

There is no need to remove leaves with powdery mildew as they can be treated.