Have you sprayed or done anything to them? You could be over watering. If thats not the case you might try a little liquid fertilizer. It is more readly available than pellet fertilizer.
As an Amazon Associate we earn from qualifying purchases. Product prices and availability are accurate as of the date/time indicated and are subject to change.
About half of mine have turned yellow, too, but I had harvested most of the peas before it got them. Most of the websites say it's a very common fungus.