Not on the plants directly. That can trap heat and will only make things worse. But rigging it as a shade cloth above the plants can help. You need a air space of at least a couple of feet between the top of the plants and the shade.

Dave

I just want to add that this year I mulched my tomatoes with a good 2-3 inch layer of hay. I've incorporated a fungicide to counter the increased disease pressure from fungus from mulching with hay, and I've taken several readings of the soil temps with that.

Research papers all lay out that tomatoes produce their best when the soils are at 85 degrees, and they start to drop in production slightly as soil temps rise.

This year I have seen bare dirt soil temps as high as 95 degrees at a depth of 4 inches. The dirt just cooks when we get these 100+ degree days, and I'm in central illinois, the normal highs are 90, not 100.

With a thin layer of hay mulch, about an inch or so (just enough to cover the dirt so you can't see soil) I saw almost no reduction in soil temps between the bare dirt and the mulched dirt.

With the thicker mulch I put around the tomatoes, about 3 inches (it has since compacted down a bit and started to decompose underneath) I see a good 10 degree reduction in soil temps. They sit right around 80 degrees, even when it turns hot.

Around the deeply mulched fruit trees, in which I set two unbroken flakes of hay on top of the soil to smother grass and conserve moisture, the soil temps are about 60 degrees no matter what the temps are during the day.

I'm not certain of anything, but I am trying to pay attention, and everything I am seeing and reading leads me to think: if you can keep as many things even as you can, if you can keep control of the things that are within your power to change like even soil moisture and sunlight exposure and soil temps, you will be able to withstand the curve balls that nature throws you, the things you cannot control.

I think that if you are seeing blossom drop like you are, make sure your soils are staying moist enough for tomato production. Once it turned hot about half of the blossoms that my tomatoes were trying to set dropped, but I have still seen impressive fruit in my tomatoes. The average daily highs for me have been around a hundred since the start of July, and I have had one of my best tomato years so far. (To be fair I hadn't really gotten the hang of gardening until this year though)

Some kind of awning above the tomatoes like 80% plastic might reduce the effect of "baking" the plants and lead to better fruit set. It could be worth a shot.