The joy of fly sheets.

Fly sheets! Possibly the number-one thing you can do to protect your horse from the nasty biting flies--deer flies, horse flies, and big ol' green-headed flies. And you don't have to spend a ton of money on them! Last year, I bought 3 new, soft and silky fly sheets for my guys, and spent less than $100--TOTAL! Now, you do have to watch for the deals, and try to buy in the off-season when possible, but good deals come up from the major suppliers all the time. (Think Dover Saddlery, State Line Tack, and TackoftheDay.com.)
You want soft fabric, not the stuff that feels like lawn chair fabric, so that it doesn't chafe your sensitive pony. A belly wrap style is great, and that way, you won't have to fly-spray your horse's belly. Neck covers are great too--as long as your horse has some shade to get into, as even the lightest fabric can cause your pony to be uncomfortably warm on those hot, steamy summer days.
For my money, NOTHING beats looking out at my horses on a hot summer day, and knowing that they are totally unconcerned with the flies buzzing around.
Next week: Night turn-out.