There are resons other than thrips,hot temps,watering and sunlight. High humidity can cause the pollen to "clump".You mention that the plants in question recieve less sun. Is it possible that they're sheltered from wind as well. Although most of the time the bloom will pollinate itself by the force of it opening up.Many people have had luck by shaking the plant a little to help it set.

Another thought is that the blossoms are setting fruit and then die. There is a name for it that i don't know but in other words it's fruit abortion. Certain viruses can cause this but I don't believe it has to be a virus for fruit abortion.You can google search that or hope for Carolyn.

Just curious if they're all the same variety. I had some Big Zacs that dropped blossoms while the Goliaths,Better Boys and Brandy Boys set fruit like crazy. Same conditions for all. Kinda overnight the Big Zac started setting fruit and now it's loaded. I'd say that the BZ was at least a month behind on setting fruit.

I have Cherokee Purples,Andru Ruhardts(spelling probably wrong),Caspian Pink and Druzbas also growing in another spot and the AR were a little behind in setting there fruit.

I know this really doesn't help but hang in there.
Hope it's soon for you.

cool thanks for the help.i have tried shaking/flicking the blossoms,but still nothing.

as i said,the early girl had fruit.but the health kick,better boy,and roma have only blossoms that fall off.

ill look into the "fruit abortion" thing.