Synthetically derived pesticides (except for some traditionals like copper sulfate) are not allowed in "organic" systems. Even the most benign and beneficial synthetically derived substance would not be allowed in an organic regimen. As for chemical premergents, they vary in their makeup, persistance and their effects.

http://www.omri.org/OMRI_brand_name_list.html
http://edis.ifas.ufl.edu/WG058
http://extoxnet.orst.edu/pips/ghindex.html

Corn Gluten Meal has a natural growth suppressing property and, as was later discovered, is a good N source and it adds organic matter to the soil. Other pre emergents rely on poisons of some kind, depends on the pre emergent which ones, to suppress growth and those are detrimental to the life of the soil microbes, like any other "weed killer".

I still don't understand or have much information about the way chemical pre-emergents work. I note from some of the information on sites posted above that some of the chemicals used are so low in toxicity to _mammals_ that it is hard to evne measure the toxicity. I grew up on a farm applying "Treflan" and have literally nearly bathed in the stuff with no obvious ill effect then or within the last 30 years.

Of course, substances that can harm plants may not harm people and vice versa, which really doesn't answer to main question I was hoping for some info on: the effect or lack thereof on soil organisms. They happily eat alot of stuff in the compost pile that would do you and me in.

So, I'm still curious about how to weigh the affects of pre-emergent lawn chemicals on the health of the soil bacteria and fungi.

I'm not selling anything as an organic producer and so am not too interested in what laws say on what it takes to be certified "organic". Just want to try to get some hard facts on if and how and to what extent chemical pre-emergents might affect soil life.

I'm willing to be pre-emergents don't all operate in the same way. Here are some MSDS sheets to get you started:

http://www.ilpi.com/msds/

And, of course, you can do a search on 'chemical pre-emergents soil' and see what hits you get.

About bathing in active synthetic chemicals: sometimes it takes a little while for results to show. Non-hodgkin's Lymphoma is showing up in later life in a lot of people who were exposed to Round-Up, and a much higher percentage of men than standard have incidences of prostate cancer between 50 and 70 if they were exposed. And then there's my favorite: you're 70% more likely to have Parkinsons if you were exposed to Pesticides, "such as those used at home or in gardening". Just cuz results don't happen this decade or the next doesn't mean you're home free.

http://www.hsph.harvard.edu/press/releases/press06262006.html

There is evidence that links certain diseases with exposures to various substances, but evidence can range from clear links, to possible links, to links with very poor evidence. Exposure to certain pesticides in large enough quantity over long enough time can be problematical, but it's important to base statements on fact, with specificity as to what pesticide is being discussed, and with a good understanding of all the evidence available. Non-hodgkins lymphoma has not been generally linked to Roundup, nor is prostate cancer linked.
Wikipedia citation: "The US Environmental Protection Agency, the EC Health and Consumer Protection Directorate, and the UN World Health Organization have all independently concluded that glyphosate is not carcinogenic. Despite this, opponents of glyphosate-based pesticides frequently claim that glyphosate is linked to cancer, citing the research of Hardell and Eriksson (Cancer 1999 85:1353Â1360). Although this paper showed a link between glyphosate and lymphoma, this link was not statistically significant and was within the realm of random variation. The authors themselves concluded "definite conclusions cannot be drawn for separate chemicals, such as MCPA and glyphosate, from the multivariate analysis"".
In fact, Roundup has been classified as showing evidence of non-carcinogenicity. This cannot be said for approximately half of all known substances, natural or synthetic.

UC Berkeley article:
http://www.berkeley.edu/news/media/releases/97legacy/11_01_97a.html

Here is a link that might be useful: Prostate cancer study

When a manufacturer of a product submits tests that show it is rather innocuous they only test the "active" ingrediant for that and do not have to test the product as it is sold to you. There is often something that happens when two chemicals are mixed that increases the potency of either one or both that changes the whole compostition of those chemicals. Most all of the popular plant killer products out ther ehave had the inert ingrediants changed several times since they were introduced, and of course you have no idea what the inert ingrediants are because it is not a requirement to list them except as "Inert Ingrediants". So the place to look for information about the produc you think you want to use is the Northwest Coalition for Alternatives to Pesticides, NCAP.

Here is a link that might be useful: NCAP

The old saying about how beggars should not be choosers comes to mind. While any info on the affects of various chemicals on us and our environment is useful, post emergent herbicides (like Roundup) effects on humans, doesn't help me weigh out the pros and cons of pre-emergent herbicides on the soil organisms.

Now, some natural substances can be as damaging to some organisms, including people, as some chemical alternatives. For instance, strong vinegar used as an herbacide can hurt people more than Roundup if not used right in the application process. I've seen some nice informative debates on here about whether chemical fertilizers do or do not "harm" soil organisms. So, I thought I'd throw out for discussion whether anyone has seen studies/info as to pre-emergents affects on the population of soil organisms.

I've wondered about that before, but haven't seen anyone that had found anything specific where that was inquired about by scientist. Like most things, its a matter of degree. If its real bad for the health of soil life, I would do without it, if its not really too bad, then its pretty helpful to take care of some problems I have cropping up.

Potential effects all depend on what specific substance is in question, since they vary so much. A few links to relevant studies:

http://www.publish.csiro.au/paper/SR05125.htm
http://www.springerlink.com/content/w741137482632757/
http://scholar.google.com/scholar?hl=en&lr=&q=cache:e0jwnsK272IJ:www.spcru.ars.usda.gov/Pubs2/1995hhsJ01.pdf
http://www.springerlink.com/content/j267731120pr1012/

Those more than willing to accept the industries position that the poisons they make are not harmful without also looking at the research done by others that indicates major problems are not keeping an open mind. There are many people that want a non toxic pesticide and there is no such thing. If anything kills something it is toxic, some more toxic than others. One person, when told that carbaryl is causing major health problems with migrant workers, stated that it was not a problem for her because she did not employ migrant workers. Do not simply accept the industries information, look other places for better information than the industry will supply.

Thanks Jayk. Very much the kind of info I was curious about.

Looks like some facts both pro and con. It would sure be nice if someone ran bigger studies on more of the ingredients used in various pre-emergents.

I've cut and pasted some of the guts here for convenience:

few significant effects of herbicides on soil organisms have been documented

At normal concentrations of 2.6 and 26 ppm, dalapon had little effect and is unlikely to harm the soil microflora or soil fertility.

In a review in 19Â78, Anderson concluded that very
few herbicides have any prolonged adverse effect on
soil bacteria. Variability in herbicidal effects have
been attributed to soil type, soil moisture, tempera-
ture, pH, nutrient availability and many other factors
(Smith, 1982).

In microcosm experiments, application of each of the test herbicides at the rates of 1, 2, and 4 µg active ingredient (a.i.) g-1 soil caused significant (p

Regarding Roundup, or "glyphosate," according to Stephanie Seneff at MIT, it works by disrupting the shikamate pathway in plants. (I'm not sure of the spelling.) People don't have a shikamate pathway so it was supposed to be benign to us. However, now we know that most of our DNA--98% is what I read and hear--is from the healthy bacteria in our bodies. Now we now have a problem. These healthy bacteria that are necessary to our health DO have a shikamate pathway and they are affected by glyphosate. It is also my understanding that glyphosate ties up minerals in the soil, making our foods mineral deficient. I have also read that it has a half life in the soil of 22 years.

The glyphosates have never been acceptable to any organic grower. Contrary to what the manufacturers told us for years that product was not as innocuous and is in our water supply as well as in our food. We are ingesting the stuff and will be for years since it is so pervasive. Now we also know that glyphosate can cause non Hodgkin's lymphoma and the manufacturer of one brand has been ordered to pay a very large sum as a result. There are more cases coming.

Any time a synthetic product is used in the environment problems occur and most of the time we do not know the results for many years and that is why organic growers will not use synthetics.