I have grown runner beans in the center of England for
several years, with good crops and healthy plants, but this year my
plants have some sort of disease. The leaves have brown spots which seem
to spread along the leaf veins and then over the whole leaf. Some plants
are still producing healthy beans, but on some plants the beans have shrivelled
and turned yellow. I don’t know if these are the same plants with the
worst leaf problems as the plants are tangled together too much. I have
looked at various websites, but am not sure that any diseases shown
correctly match my problem. I would be very grateful if you have any
idea as to what it is and how to deal with it.
While I cannot diagnose the problem remotely, your description does sound
quite a bit like anthracnose, which is a fungal disease. According to The
Organic Gardener’s Handbook of Natural Insect and Disease Control by
Barbara Ellis (Rodale Press, 1996), this disease thrives in wet, humid
conditions. You would see leaves with dark streaks, and black petioles
and veins on the underside of the leaves. If this is indeed the problem,
plants may be sprayed with sulfur, or you can seek out resistant
cultivars next time around (‘Espada,’ ‘Marbel,’ Morgane,’ and ‘Rocdor’
are a few).
On the other hand, the yellowing of the seed pods sounds more like
bacterial blight, also encouraged by warm, damp weather. If your plants
are not forming any new pods, remove and destroy them. Next time you
plant, be sure there is adequate space between plants, and perhaps
rotating the crop to a different location might help.
Just to give you some basis of comparison, here are links to sites with
information about diseases affecting beans:
Cornell University Vegetable MD Online
University of California, Davis Integrated Pest Management
Royal Horticultural Society lists several problems affecting runner beans. There is a fungal disease of broad beans called chocolate spot which sounds a little like what you describe.