Baking soda isn't going to do the job. Its a myth that became widely promulgated on the Internet.

Quote from this article: "In 1985, Dr. Horst, working at Cornell University, started testing the effectiveness of sodium bicarbonate on garden fungi, like powdery mildew and black spot on roses. “During scientific trials, incomplete information was reported in a gardening publication that ultimately found its way into the public domain”, (ref 1). Other writers picked up on the information, filled in the details of the formula and gave it a name – the Cornell Formula.

Dr. Horst says, “There is no such formula.” “With the advent of the Internet,” says Dr. Horst, “The myth of the so-called ‘Cornell Formula’ continues to spread and I feel that the record needs to be set straight. Many of the formulas that are promoted in articles and forums are simply inferior and may have adverse impacts.”

I knew Dr. Duane Coyier at OSU (Oregon State) in the 2000's and his team studied the "Cornell Formula" in field trials. They found that baking soda had minimal effect in suppressing fungal diseases, but it had the ability to cause significant damage to the roses: burned/killed foliage, stunting and dwarfing of new growth, reduced bloom production, and overall reduction in the health and performance of the plants. Don't waste your time on baking soda - use a fungicide designed to do the job: propiconazole (sold under various brand names). Its been studied and evaluated, and will not damage your roses when applied as directed, and poses very little risk to the environment (nothing is zero risk, not even baking soda. We can thank Jerry Baker for introducing some serious nonsense about gardening "home remedies" Ugh). The "Cornell Formula" is probably more damaging to the soil biome than the tiny amount of propiconazole needed to control fungal pathogens on roses.

Now, I'm no fan of using man-made chemicals in the garden unless it becomes absolutely necessary, but I embrace them when I have no better option. I grew up in the era of "Better Living Through Chemistry" so I know what an unfortunate path that philosophy led us down. But there are plenty of "home remedies" that have been written about, promoted and shared, many of which are totally useless (or nearly so) and in many cases have far more potential to cause serious damage to the environment than a carefully engineered fungicide like those designed to suppress disease in roses. If you have only a dozen or so roses, and you use the fungicide only on the ones that need it, and only when needed, then you're not going to damage anything, you're not going to harm yourself, your family, your pets, or your roses. In fact, you're making the wiser choice by choosing something that targets the problem specifically.

And if you aren't comfortable with that approach, you'll be smart to get rid of that rose and find a variety that isn't as tragically prone to Rust as the one in your photos. Myself, I wouldn't tolerate such an unhealthy rose in my garden. There are tens of thousands of roses to choose from, and many will perform better for you.