I would not recommend disinfecting/cleansing the soil you will kill off all the wee beasties in it good and bad, and it would be risky to grow veggies in afterwards. The bug your describe is not likely to have attacked your potatoes - much more likely to have been small slugs. Yellow mottling on your runner bean leaves is probably a mineral deficiency - they need very well manured soil to do well and lots of water. Do you rotate your crops each year, if not you are risking a build up of disease in the soil.

My climbing French beans also have yellowed leaves this year although on a site that hasn't had them before, and that has been well manured - doesn't help you, but you're not alone.

Many thanks for your answer Moon growe, get up the local stables and sort things out for next year.
Andy

If i am not too late in answering ... Definitely wire worms - any you find ... kill! When you dig over the soil this autumn grab them and squish them quick. They do move fast, and will eat holes in most root crops. Makes veg unsightly but not inedible, but high infestation can take out a whole crop. Moon Growe's suggestion of crop rotation will keep this under some control. Also your runner beans are definitely lacking something as Moon Growe suggests - nitrogen, potassium, sulphur, manganese??? They are heavy feeders - try filling trench/hole with part rotted veg waste about six weeks before planting bean seeds, and then feed weekly during a water, until they stop flowering or you decide you have had enough beans!