Clip all feathers off that you see larva on that you are unable to wash off.
Wash with antibacterial hand soap and rinse well.
or
This is a mixture I found to put in garbage cans but not sure if good on a chicken. If I were desperate enough, Id try it but rinse thoroughly when done. The ingredients all seem safe.
Mix 1/2 cup table salt, 1 cup lime juice and 3 cups white vinegar inside a spray bottle. Shake the bottle vigorously to mix the three ingredients.
Spray the areas infected but not the wound as I'm not sure this would be a good on the wound. Leave on for 5min then rinse thoroughly and dry thoroughly. Maggots like moist dam areas.
or
This lady out of desperation used hair spray and said it worked.
"Anyway, I surfed frantically for anything that could kill maggots without killing the chicken (and that I had in the house). Hairspray! So I went out and covered my chicken with Harmony hairspray and thought that I would take her the the vet in the morning if she was still alive. Well, this morning had a look and the chuck is loads perkier and the maggots (literally thousands of little ones) were pretty much all dead! So I cut off her feathers with scissors and washed the area with soapy water and a toothbrush- looks quite clean and OK now!"
http://www.horseandhound.co.uk/forums/showthread.php?371820-HELP-My-chicken-has-maggots!!!
Other sites say to put "Swat", a cream to put on horse wounds that flies are getting on. You can get this at
tractor Supply or most any Farm ranch store. I use this product on my dogs' ears if the flies bite the tips of their ears. It keeps the flies off, and kills larva for a day and also keeps the scab soft and quicker heal. Will need to apply every day. It wears off.
Whatever you do, you will need to isolate your rooster in an indoor area from the others or they will peck at the wound and make it worse AND more flies will quickly come lay more eggs. It only takes 1.
Maggot wound step by step help.
https://www.backyardchickens.com/t/231156/wound-with-maggots-and-bad-smell
Go to your local store tomorrow and get Epsom salt. Long shelf life, cheep and you'll never know when you'll need it for yourself or an animal. Good stuff to have around.
ps. on hydrogen peroxide. It is good for a one time does on a very badly infected wound but do not use repeatedly. It kills healthy skin around a open wounds. Ok for small soars or scratches but not so good for open wounds. Vets and Doctors have gotten away from this product and use saline solution which is basically boiled water or purified water with table salts added to it. Salt is a very old remedy for killing bacteria......still is.