There was a product called Blossum Set I used years ago to stop the blossums from dropping off when the temperature fell below 55 degrees. It really worked but I can no longer find it.

Do you remember who the manufactor is? If so, we might be able to find their web page and send email asking about the product.

I think it was Ortho - I checked their site but could not find it. All I remember was its name "Blossom Set" and it was termed a hormone.