Answer: Corn gluten is a natural, organic product that can be used to prevent crabgrass and other annual weeds from germinating. It does not harm people or animals, and it is added to some bird feeds.
Preen is a brand name line of pre-emergent herbicide applied to stop weeds from germinating in flower beds and similar areas. I believe there is a new organic Preen product containing corn gluten for use in vegetable gardens and other areas. Please check their web site or contact the manufacturer directly for specific information about whether or not it would harm birds; although corn gluten should be okay I do not know the full ingredient list.
Q&A Library Searching Tips