Since corn gluten meal kills only seeds, not existing weeds, it should be spread in the cooler months so that the weeds do not have a chance to grow again.
Yes it has been shown to be an effective weed barrier in some areas however it does attract some insects at the same time. Many people in the warmer areas refuse to use corn meal for this reason. You may try adding red pepper to the mixer to dissuade ants from hanging out in the area.
You need to put the corn gluten down at the end of winter or very early in the spring. It does not kill existing weeds, it just causes them not to germinate, so you need to catch them before they grow.
