Water melon

My attempt at growing water melons has been slow going due to the cold spring and indifferent June and July, but the last couple of warm spells seemed to give them a spurt in growth and they have been setting fruit in the last week.
Just as that has happened I've noticed some wilted leaves in the last couple of days, and looking at the stems on one plant they appear scabby.
Not sure what it is but I'm sure it may well affect other members of the Cucurbit family.