Selfsufficientish.com

I have a weed growing in my garden that has become covered in a rust coloured rash. What is it and can it spread to my other plants?

It could be Rust, which affects peas, beans, sweetcorn and leeks to name a few. It flourishes in cool damp weather as it's a fungus and can stunt the growth on those plants affected so much that they will be pretty much useless.
Or hopefully not.

Google for "rust disease" and select "images" to see if that's what you have.

If it's one of the sow thistles (non-prickly thistle, lobed leaf, yellow fower going to fly-away seeds a bit like dandelion) then we've spotted the same thing on our plot.

Individual rusts are generally specific to particular families of plants, so you shouldn't really worry unless the weed is closely related to any plants you cherish. In other words, pea rust isn't the same as leek rust isn't the same as thistle rust, etc., although many of them can look very similar.

I must have had a right old cocktail a couple of years ago then.
It started on the bracken on neighbouring farmland and destroyed my peas, runner beans, broad beans, leeks, sweetcorn and then spread to the wild montbretia on my road boundary.
I have to say it was the first time it happened and thank goodness it hasn't happened since.

Thank you for the tips, it might be what has affected my peas this year.