Swarming can be reduced but it will require some annual testing on your part to figure out what works best for you. As stated previously, read the writings of Walt Wright and find the thread by Matt Davey on opening the sides of the broodnest. It is great info. I do think that if your bees are swarming in August, There must be something you need to adjust to in order to prevent it. Bees generally don't want to swarm that late in the year unless there is a problem. I have never found that taking frames of brood will stop or slow down the swarming impulse. Taking the queen out will but clearly you don't want to do that.