A lot has been written about what temperature is needed or ideal for fruit setting with Tomatoes. From everything I have read somewhere below the upper or perhaps mid 50s fahrenheit or around 14° C tomato fruit set is impaired or stopped altogether due to the inability of the pollen to form. Is there a hard temperature number, due not cross this line or all hope is lost on the bloom or is more of an exposure at such and such temperature for x amount of time kind of deal?

I’m not really interested so much in the cold set types like Glacier or Stupice, but the mid or late season well known heirloom/OP indeterminates.
Forecast here has some upcoming nights bottoming out at 53° F, 12° C, but that temperature might be only achieved a couple of hours before dawn. What if most the night is 60° or in the high 50s and only a few hours gets into the danger zone, does that mean that bloom is done, no hope of setting?

Just wondering what the rules are and how firm are they. Or is there some wiggle room?

That was the original intention of the blossom set spray they sell.
Cold temperatures not hot temperatures.
Some varieties do better in the cold than others.
Gregory's Alti is one of them.
Forgive the spelling.

here in the PNW, for me, once the night temperatures are over 10° C I'm OK putting out my tomato babies .... and, I recall reading that a bit of cold is good for future increased fruit set ..... will see if I can find the article

worth1 wrote: ↑Thu Mar 09, 2023 11:36 am That was the original intention of the blossom set spray they sell.
Cold temperatures not hot temperatures.
Some varieties do better in the cold than others.
Gregory's Alti is one of them.
Forgive the spelling.

I grew that one last season (transplanted in February) and it was the probably the most vigorous tomato for the first month or 6 weeks. I don’t remember the nighttime temperatures when it set fruit. GA set a lot of fruit and the first ones were pretty, but as the heat increased, the fruit became less pretty. I almost grew GA again, but decided to give some others a shot.

so, here is what I'm was thinking about, but does state cold treatment does not impact blossom set, just number of blossoms, so does not answer your question ....

"from Growing greenhouse tomatoes in soil and in soilless media Dr. A.P. Papadopoulos Research Centre Harrow, Ontario

Under a cold treatment regimen, place young tomato seedlings in a day and night air temperature of 50-55F/10-13C for approximately 2 weeks, while providing as much light as possible for 9-12 hours. Seedlings should be subjected to cold treatment just after the seed leaves (cotyledons) unfold and the first true leaves start to appear (see below). Shoots kept at low temperatures at this stage of growth produce a small number of leaves below the first flower cluster and therefore flower earlier; roots kept at low temperatures cause branched clusters, i.e., many flowers in the first and possibly the second cluster. Cold temperatures during both day and night are effective.

stages in seedling growth used for initiating (plant A) and terminating (plant B) the cold treatments

The cold treatment increases the number of flowers but does not influence the setting of fruit. If later conditions for fruit setting are right, a greater number of flowers will set fruit because of the increased number of blossoms. If, however, the temperature for fruit set remains less than ideal, the pollen does not germinate and grow normally, resulting in poor fruit set and cat-faced fruit. When the cold treatment is used, seed 10-14 days earlier than usual to compensate for the slow growth rate during the cold treatment. The growth medium in the seedling trays must be sterile, because when plants are grown at relatively low temperature the danger of damping-off is increased."

Cold temperatures also have been reported to increase the incidence of fused blossoms. Some people like to discard these fruits while others like to grow them into monster tomatoes.

In early spring I don't worry about nighttime lows dropping into the high 40's. Yes, it does take longer to set in cool temperatures. Nighttime lows of 50F and daytime highs of only 60F are still fine for the tomatoes bred and selected here, they will grow and set. If the daytime high doesn't reach 60 F, it is not a 'tomato growing degree day'. They will hold their flowers at daytime highs of just 50F, at least for 3-4 days, and do not drop blossoms they just don't set or grow anything until it warms up, so it takes longer.
The problem for beefs, if they're flowering and ready to set in cold temperatures, you will often get uneven pollination ie catfacing. Megablooms also are prompted to form in cold weather, and these can be ugly, uneven tomatoes. IDK if buzzing would help, I think the problem is that the sun warms part of the fruit but the shaded parts don't get the same temperature needed to mature at the same time. But I believe we are talking about lows down in the 40's and days below 60F for the serious cold stress to produce that.
The same temperature constraints apply to quite a few of the mid to late heirlooms I've trialed here. 50F nights are the benchmark for Aok.
But some of the mid and later heirlooms I have grown, I did find a number that will not set, or will not grow the fruit they set, if nights are consistently below 60F. The 60F night is a real benchmark for ideal fruit forming conditions for those larger tomatoes. That doesn't mean an occasional night in the 50's would be a problem for most, but it's hard to say. All varieties have their own preference and limits.

Is there any science to the sprays? I find many tomatoes just drop the flower since summer can be cold here. I wonder if the spray would help.