I think the problem with temperatures, to me anyway, is whether they are being measured in the sun at daylily flower height or, as in official weather forecasts/reports etc., in the shade at a specified height above the ground. The "official" temperature for any given hour in the shade is going to be quite different from what a daylily flower in the sun is experiencing.
Also perhaps there are variations according to cultivar and maybe those working in the south have, over time, developed cultivars that function at higher temperatures than daylilies in the north?
Oscie Whatley, in an article on hybridizing, re-published on the AHS web site here:
http://www.daylilies.org/Whatl...
"Temperature: Probably all varieties have a shut down temperature for the pod parent. I am not sure of the low side but the high side seems to be around 90 degrees F for tetraploids and a little higher for diploids with some variation for each variety. I believe pollen has a higher range but haven't tested it."
I checked when Hemerocallis lilioasphodelus flowers here for the last couple of years and typically gets loaded with bee pods, and the temperature only reached 80F or slightly above as an afternoon high temperature on a few days during those flowering periods.
Toru Arisumi of the USDA, Beltsville, Maryland did some studies on the cultivar 'Purity'. He pollinated at 75F and 85F and maintained the plants at those temperatures until seed harvest. He said "Seed set was good at 75F and poor at 85F".
There is an article on hybridizing in the American Hemerocallis Society's 2002 Daylily Handbook called "Breeding of Diploid Daylilies". Quote: "........crosses should be made as soon as the anthers containing the pollen have opened and the pollen is plainly visible. Crosses may be made earlier. By squeezing the anthers end to end, the anthers may be made to open and the pollen used. A dry morning with a temperature of 72F is ideal. Early pollination is advised because pollen dries rather quickly on a hot day and by noon it may have blown away, shaken out, or been knocked off by bees or other insects." The author goes on to say that pollination is better before the temperature gets to 90F, and says "it is estimated that three hours below 90 (optimum 72 to 80F) are required for the pollen tube to begin growing down the style into the ovary".
So there seems to be more or less a consensus on the high temperature, but not so much for the low. It's noon here on 1st August, the sun is shining and the temperature is currently 74F. If the stigmatic fluid didn't start until 80F then no pollen should be activating here yet today where the "normal" high for the time of year is 78.8F. We'll find out since I was out there happily slopping on pollen an hour or so ago
Edited to add this link to the AHS PDF "Daylily Fertility Tips" which gives opinions of Darrel Apps, Pat Stamile, Karol Emmerich, Jack Carpenter, Curt Hanson, Dan Trimmer, Melanie Mason, Maurice Dow and others:
http://www.daylilies.org/2007D...
