Does this look familiar? I know. Itching is not necessarily a grooming issue. There can be all kinds of reasons for itching. You might even have a horse with a bad case of pinworms, which results in an overnight loss of tail hair and a good patch or two on the haunches.
BUT. Keep in mind that the flies during the summer are horrendous. Whether or not your horse has full anti fly armor or not, they're probably rolling, scratching, rolling some more, rolling in muck, getting wet, rolling in new muck... You get the idea.
Here's the thing. No matter how much clothing you've got on your horse, they have dirt down near their skin. It's common sense to bathe that off and start over - so to speak - every once in awhile. If your horse is so twitchy that you're practically dancing to keep out from under their hooves, it might be time to step up your game.
This shouldn't just be a bath with your average moisturizing shampoo either. Find yourself a good Anti-Seborrheic Shampoo. This combination of salicylic acid, coal tar, and micronized sulfur will really get the itch out. If you can't find any at a local store and you feel like you have an emergency, you can purchase it directly from Thal Equine in Santa Fe.
Now, this is going to be a serious bath. You need to soak your horse with a good prewash. Then mix the soap into a big bucket of water and use one of those enormous car wash sponges to get a good lather going. When you lather up that nasty, dirt caked coat, get everywhere. Let the suds run down the horse's sides and don't be afraid to get the sponge nice and full of soap and water and just let the suds fly!
A great rinse cycle is critical here. You can't leave any bit of soap next to your horse's skin or you'll start the cycle all over again. Once you've rinsed, make sure to walk your horse or tie them where they can't roll. I know. It's almost impossible to keep them clean while they dry off. But see, the climate is working for you here. Just walk them around a few laps in the hot sun and you'll both be dried out.
There's no need to over bathe your horse when they're itching, but keep an eye on the dirt and itch factor and don't be afraid to pull out the hose and the soap and get down to business when you feel the itch factor has exceeded your horse's tolerance. And don't worry, fall is coming. I promise.