Preen is a pre-emergent herbicide. It keeps seeds from germinating. It doesn't effect existing plants. I think it's long term effects on the environment are minimal.

Christine, I always like the questions you ask, because I am usually wondering the same thing, but too afraid to ask.
But anyway, I came across the website for Preen and the product sounds good, only IF you follow the directions that are given. The only harm will occur if the product is applied around new seedlings. From the information I have read, I might as well use CGM.

Here is a link that might be useful: Product Info

Actually, I did use CGM, but I think I used it too late. Many, many weeds were out not only in full force, but in bloom. Hopefully it'll deter the knotweed later in the year, though.

Thanks for the link. :)
Christine

EVERYONE'S inside a watershed -- unless they're on the moon. If they're not in the Chesapeake Bay watershed, maybe they're in the Mississippi watershed?

So why would one suppose the commercial website selling an herbicide would not make it sound good? How about reading about the chemical in Preen, trifluraline. Since corn gluten meal is an equally effective and completely nontoxic preemergent, there is no reason to prefer preen. (except that the cost of buying it vs. the environmnetal cost, is probably lower)

# Soil Microorganisms: No information available.
# Plants: Trifluralin did not accumulate in crops grown in silt loam soil treated with 1 pound active ingredient per acre. Contact with susceptible non-target plants may injure these plants.
# Aquatic Animals:Trifluralin is highly toxic to cold- and warm-water fish and to aquatic invertebrate animals. It is very highly toxic to amphibians (tadpoles). It has not been tested for effects on estuarine and marine animals. It may build up (bioaccumulate) in fish exposed to trifluralin in water at low levels; but in one test it was eliminated from edible fish tissues 7 days after exposure ended. Trifluralin affected the survival of minnows at chronic exposures as low as 5.1 ppb; and affected the survival of water fleas at chronic exposures as low as 7.2 ppb.

Reported effects: Most incidents of trifluralin exposure reported in humans have involved dermal and eye irritation and nausea. Dizziness and headache, fever or chills, and muscle aches or weakness have also been reported.

Potential for adverse health effects from inert ingredients contained in the formulated product: Inert ingredients found in the emulsifiable concentrate (E.C.) of trifluralin include xylene, ethylbenzene and naphthalene. The effects of these compounds include: corneal (eye) damage, liver changes, fetotoxicity, and teratogenicity (xylene); blistering of skin, and liver, kidney and testicular changes (ethylbenzene); and cataracts and liver changes (naphthalene).

Health effects of exposure to formulated products: The Trifluralin E.C. formulation may cause skin and eye irritation. No specific effects of exposure to the granular formulation have been noted.

Health effects associated with contaminants: Trifluralin contains the contaminant N-nitroso-di-n-propylamine (NDPA). This contaminant is an N-nitrosamine class chemical; these chemicals have a known potential for causing cancer. However, the Environmental Protection Agency (EPA) requires that manufacturers of trifluralin certify that technical trifluralin products contain a total N-nitrosamine concentration of no greater than 0.5 ppm. The EPA concluded that the benefits of trifluralin outweighed the identified risks. They also conclude that exposure to NDPA in trifluralin is not of toxicological significance in evaluating the risk of exposure to trifluralin.

Here is a link that might be useful: Pesticide fact sheet

Hi Christine,

Here's a whole lot of information on Preen. I would have linked to it yesterday, but the site was down.

Alfie

Here is a link that might be useful: Pesticide Action Network: Preen