This is the leaf canopy for the Musica pole beans. The trellis is 8 foot tall and the vines are over the top and loaded with beans. The top of the canopy looks dark green and healthy but look at the bottom. The leaves are starting to yellow and are mottled. Since taking this photo last week, the yellowing is now half way up the vines, so it spreads fast.
Here is a closer look. The leaf at the top is showing the top surface and the lower leaf is flipped over to show the underside. The leaves are yellow with a mottled pattern.
From what I can gather, this looks like Bean Golden Mosaic virus, something I have never encountered before. It is fatal and all you can do is remove the plants and destroy them. It is not a seed-borne disease, which makes sense because these plants came from the same seed packet I used successfully last year. The disease is spread by insects, most likely aphids or whiteflies. That is puzzling because I generally never see an aphid in my garden. I have Japanese Beetles taking up their favorite dining spot at the top of the vines, but no aphids.
BGM is apparently a major problem in South America, Mexico, and parts of southern US and limits production of bean crops in those areas. Any legume plant can host the disease, including all the clover and vetch I have growing as weeds in the paths in the garden. Serves me right for not keeping up with my weeding. I hope to be able to at least harvest the pods now on the vines, but it does affect pods and I am starting to see signs of that. My Gold Marie bean plants did poorly right from the start but their leaves don’t look this. I don’t know what their problem is but that crop is mostly lost.