Yes, during the summer it is too hot for worms. We usually start deworming in October (usually with ivermecting/praziquantal) and once more in the spring (2x yearly). If you wish to use regular ivermectin you deworm 3 or 4 times instead of 2.
If find it is cheaper to just do ivermectin/praziquantel 2x yearly and that way I don't have to worry about Tapeworms. Tapeworms don't or rarely show up on fecals anyway.