A lot of rain on our farm (About 2 inches in the last week -- west of London) - looks to be giving weeds a bit of a boost on our corn crop. Not sure if you are in the same situation or not - but a couple of resources here that you may be interested in....
First -- WeedPro75 from OMAFRA. A big help in making sure the right tank mix is applied - at the right price.
Second - a video from Clarence Swanton about what weeds do to corn crop. I was surprised to hear that it would have a big impact on emerging corn.