>My recollection is that Roundup is just glyphosphate and Rodeo containes the
>surfactant.

Other way around, which is why Roundup must not be used near wetlands. The
surfactant is more toxic than the active ingredient (especially to aquatic
organisms) which is unfortunatly not uncommon with pesticides and household
products. Because of the trade secrets act, much harmful stuff can legally
be hidden in the innocuous sounding 'inactive' ingredients part of the
label. As for the glyphosate, it binds well to clays and organics so
runoff isn't usually a serious problem, though in very sterile sandy soils
it could happen. Half-life for breakdown varies tremendously from 1 to 174
days, depending on soil and bacterial conditions, with an average half-life
of 47 days (for those not used to half-lives: 1/8 of what you apply will
still be in the soil 5 months later under 'average' conditions).
Glyphosate does not break down significantly in sunlight as at least one
syndicated gardening writer keeps insisting, it needs to be metabolized by
bacteria. I don't know about the surfactant, it's hard to find reliable
information about it because it seems they aren't required to publish the
data they have, or perhaps even to do environmental tests on it at all
because it's 'inactive'. I'm still fuzzy about the requirements for
inactive ingredients. Always read and follow the label, it's the only real
guide to sort-of safe use of a product as a whole...

Much useful pesticide information can be found at the excellent ExToxNet
site, <http://ace.ace.orst.edu/info/extoxnet/> and at
<http://ace.ace.orst.edu/info/nptn/factshts.htm>. The glyphosate Pesticide
Information Profile, which includes references, can be found at
<http://ace.ace.orst.edu/info/extoxnet/pips/glyphosa.htm>.


On the whole, between noxious weeds and properly applied roundup, I'll
chose the roundup, surfactant and all. Tolerating a stand of invasive
weeds is a much bigger threat to habitat, and even though the land is going
to be farmed rather than restored, at least it's some improvement by
reducing the amount of weed seed produced.

Allyn Weaks allyn at teleport.com
Seattle, WA USDA zone 7-8
Pacific NW Native Plant Gardening: http://www.teleport.com/~allyn/natives/