Welcome to GoY.
firstly do you know which plant it is?
have these just appeared and is it on the older leaves only or on all of them?
If it is a developing situation then it looks like a fungal infection. Depends on which plant it is as to which fungal infection it is and the relevant treatment.

lastly and I know this sounds daft but have you painted any fences near by. [we had a plant that suddenly developed beige spots and I was baffled until I saw hubby shaking dry a paint brush over the plants by the garage.]

Power washing detergents can have a similar effect. Oil sprays can do the same, if the temperatures are over 85º F within 24 hours.

Hi thanks for replying the plant is Rudbeckia Goldstrum and the photo is from a leaf lower down on the plant the top leaves seem to be ok