Augie is correct and caution SHOULD be used if you're using Preen. That's why I recommend corn gluten due to the Treflan being hazardous to waterways and some of our 'good' bugs.
The active ingredient in Preen is trifluralin, ie: Treflan
It is a pre-emerge herbicide that is quite toxic to fish and aquatic invertibrates, and is known to be an endocrine disrupter in mammals. Corn gluten is not a component of Preen, but it does use ground corn cob as the carrier material for the active ingredient.
I’ll use Preen on Mrs. Augie’s flower beds, but I don’t want it anywhere near my victory garden.
I hate pulling weeds, so I may pick up some corn gluten this spring and give that a try.
Augie is correct and caution SHOULD be used if you're using Preen. That's why I recommend corn gluten due to the Treflan being hazardous to waterways and some of our 'good' bugs.