| The Blossom Set spray you're using was designed to be used in cool weather areas b'c it bypasses pollination when temps are too COOL for pollination. Jim is no doubt spot on with the high temps found in Las Vegas right now. Blossoms won't pollinate when temps are much over about 90-95 nor when night temps are above 70. Misting the blossoms isn't going to help b/c that causes pollen clumping in addition to the heat problem.\ The only other deterrent to pollination other than what's been mentioned here is growing in too rich soil or overfertilizing; both can inhibit both blossom formation AND fruit set. But I would think that your main problem is high temps. I also wanted to point out for future reference that at the top of this page there is a link to the main Tomato Forum where problems like this are discussed. In addition, there's a FAQ at the top of that forum all about blossom drop ( lack of pollination). Carolyn | 
