My son has a wonderful veggie garden (in Crete), but his cucumber plant doesn’t look healthy! I said I would ask you, as I am a Toronto gardener.
Thank you for contacting the Toronto Master Gardeners concerning your son’s cucumber plant.
This problem could be caused by the striped cucumber beetle. That being said, I’m not sure how prevalent this pest is on the Island of Crete, your son should confer with other cucumber growers around him to see if they have been effected too.
I’m attaching an information sheet which I hope you and your son find helpful even though it speaks from a north American perspective.
Striped Cucumber Beetle | eOrganic