Kelp is very good for them but you do no need to do the kelp if you want.just a suggestion !
Feed Apple cider vinegar and and garlic .and if on grain I'd slowly stop and switch to apples and carrots And kelp
Yes, a pony that I rode got a huge on right were the bit sits.
Last summer I used the injectable ivermectin and a fly sheet with flyspray and he still managed to get one but this time it was in his eye.
A summer sore is worm eggs transferred by flies and when the fly bites the eggs make a sore and the eggs continue to grow and are one of the hardest things to take care of lol
I believe that once a horse gets a summer sore they will get them more often and more easily. Our vet had us use dmso mixed with ivymectrin and nutrafurazone but **CHECK WITH YOUR VET FIRST***
Hope this helps!
By summer sores do you mean scratches ? If so I have tried everything and apple cider vinager is like a miracle works really well and is super cheap. I mix 1/3 vinager to 2/3 water and spray area.