It a good theory, but who is to say that the outside weather is the 'perfect' conditions? there are reasons why some plants are annuals and produce huge amounts of seeds because a lot wont survive. The conditions you create inside are much better conditions to help a plant survive. I think we...
check out
http://www.icmag.com/ic/showthread.php?t=11688
ive copied and paste the relevant part:-
Powdery Mildew
Mildew spores can be brought into the grow room through air ventilation into your grow room, your cloths, pets and be carried by animals outdoors. and land on the plant...
Sorry to bump an old old thread, i think what the OP was on about was in regards to this
http://greenmanspage.com/guides/yield.html
i assumed it was a spelling mistake, but would like to know what 'ethel' is or is supposed to be