I've noticed in past years that when my cucumber vines get about 3 feet long, SOMETHING happens to the growing tip. It gets kind of brown up one side of the stem. The tip curls over and then dies. Eventually the tip-less vine makes one or more side branch and the vine grows on but sometimes the new tips die off too. Today I noticed the first tips starting to be affected for this year. So what does that? I've never seen any visible pest. I haven't used a magnifying glass or anything.
Steve in the Adirondacks