Thanks for the advice all. The temps around here have dropped back into the 70s and guess what: cucumbers are appearing all over the place! So I guess the problem was indeed heat stress. Biggest challenge now is getting some more trellises in place, the vines are invading the tomato patch. I just planted a 2nd crop, variety is "Muncher". I selected it very scientifically: it was the only remaining packet of cucumber seeds in the county. Found at a dollar store, everywhere else has replaced seeds with lawn products or back-to-school supplies.
