I planted a single borage plant in 2014 but it succumbed very early to an infestation of squash bugs. So I don't have much experience with it, although I found the leaves and flowers very tasty. I hope to plant a lot more in 2015.
I just stumbled by accident over this detail in a post by John Polk in a honeybee plantings discussion:
As a companion plant for tomatoes, it [borage] will eliminate, or reduce hornworm problems.
Borage acts as a deterrent to tomato hornworms and cabbage worms and is known to attract bees and wasps.
Some independent Googling turns up hundreds of references to the notion that borage deters hornworms and is therefore a good companion planting for tomatoes. But most of those references are like the ones here -- brief sentences without much detail. And often (out on the web) prefaced by weasel words like "it is said" and "I have heard". The way this lore appears in so many places with so little detail, it "feels" like one of those things that everybody thinks they know but nobody really has tested or tried to prove. Often if you really did into these bits of lore they turn out to be something printed in a farmer's almanac 200 years ago by some almanac-selling dude prone to making stuff up.
Did you know the tomato horn worm is edible?
A question on this developed on should some tomatoes be grown to feed this worm?
I can not raise the horn worm because I have a large number of wasps that live off the horn worm.
But in areas without such one could raise the horn worm for chicken feed or people feed.
It tastes something like a shrimp if prepared right.
Does drinking enoughwater and getting enough sleep make you immune to the flu/sickness. NOPE, but I am pretty sure it helps. (not even the flu vaccine provider will say that).
I would assume that borage helps other insects to out compete the hornworm and also confuses them with it's aromatics/color/shape, but if the farms on all 4 side of you are overrun by hornworm, a miracle might not be in store for the tomatoes.