Before you spray what kind of barrier are you planing to put up to keep the wind drift and runoff from your neighbors plants. Even the best sprayer will have drift. It sounds like you have seldom used a weed killer so it might be good to do some research before using any thing.

A layer of mulch under the fence or barrier could keep the plants out of your yard. Of course you might want to talk to your neighbor to see if there are any plants from your yard that they have problems with. Perhaps a day working together would make the fence area better for both of you.

The glyphosate products must be absorbed by a plants green tissue, the leaves. If due care is used to prevent drift those other plants probably will be safe from this very destructive, and environmentally unfriendly, poison

Round up is a contact pesticide. Once it dries, it is gone,but has had its affect. So about 20 minutes or less after application, a rain will not cause run-off problems even over a large area. It is one of the safest pesticides to use for this reason.

It does affect all plants, though, so any herbacious plant it touches will die, including grass. Evan the fine mist can "drift" and affect plants you don't want to affect.

I don't know how long of a property line you are talking about. A hand sprayer with the round up applied at a low spray setting or a drip setting, in no wind and close to the plants should not be a problem.

And definitely work with your neighbor if your properties are that close.

When tested the active ingrediant, glyphosate, does have a short life in the environment, unfortunately since no gtesting of the product as sold to you is required no one has any real idea what happens to the product in the environment. Think Love Canal and many other EPA hazardous waste site throughout the USA that are still being cleaned up after the chemical companies simply dumped several chemicals on the ground where they made them.

We live on a farm and the county tests the stream that runs through the area. So does the nearby city for water quality control.
There is such a thing as real life testing in the environment, so these chemicals' affects are known.

Natural pig manure has shown up and the consequent algae blooms,and it was stopped. No roundup/glyphosphate has ever shown up. Fields run along this stream for many miles, so it would surely show up sometime over the years if it was a problem

On the other hand,some strong pesticides have washed into a pond nearby, resulting in fish kills. Some of these pesticides have been banned.

On the other hand, DDT was banned from observation/data in the field, with no lab testing to support the banning of this dangerous chemical.
Each case is unique.

Round up has occasionally shown up here in the water before treating. Although it does not normally run off when someone applies enough that the plants drip. Any chemical can run off. Having had a neighbor destroy my collection of woodland rescues because of this type of runoff I always try to caution about run off. Most people that use chemicals do not know anything about the chemical other than the bare minium on the tag. I will see if I can find our water treatment report showing the chemicals that were found. Makes for interesting reading.

Sorry, the 2009 report is not out yet. The time frame is from July 1 to following July 1. But here is the 2008 report. You will need a pdf reader and will have to expand the report in sections to read but you will be able to see a representative water report. Most states you can look at your area's report from your state DNR or local water company.

Here is a link that might be useful: 2008 water quality report

thanks for the info. I was only referring to the stream in my post. I'm sure different areas with different soil types have different results.

The USEPA has found identifiable glyphosate products in surface as well as ground water in many places, including areas where none has been applied. Many peole, undoubtably, drink the residue of glyuphosates daily and since where it has been applied genetic mutation of lower orders of life have been observed there is every reason to believe that could do the same to humans.

Our stream is the Missouri river. Rather than have to worry about the intake being above water level as has happened to several cities around here the city has a series of wells close to the river plus the regular intake.

Thanks again for the input. Your stream is significantly larger than ours! There is all sorts of information to be found on this hot topic. It's definitely one that requires research and debate. I did find that exposure to it, such as by farmers, can increase the risk of a type of non-Hodgkin's lymphoma. That is a definite concern.
Probably what will put the end to Roundup use will be weeds' increased resistance to it, such is being seen in mares tail (horse tail). Nature always has a way of surviving.

A number of the answers that you received about how safe Round-Up are not consistent with the scientific literature, see the thread linked to below.

Here is a link that might be useful: link for above

The USEPA approves a product based on the manufacturers testing report and only requires that the ingrediants be tested individually not as they are sold. So the manufacturer can find that the active ingrediant reacts thus and so and can combine ithat active ingrediant with somehting that is GRAS (Generally Rocognized As Safe) but no one needs to test that combination to see what it does. We know, from long history, that often when two relatively innocuous chemicals are combined they produce a very hazardous product, often one no one even thought of. This is why there are many superfund hazardous waste sites around the country that are now being cleaned up and will continue to be cleaned up for, at best guess, generations.
The best thing the USEPA could do is copy that action of the Province of Canada and ban the cosmetic sale and use of all pesticdes, herbicides, and fungicides.

kimmsr gives a general description of what can happen with mixtures. Here is a specific published scientific study of this occuring:

Title: Glyphosate-based herbicides are toxic and endocrine disruptors in human cell lines.

Authors: Gasnier, Celine; Dumont, Coralie; Benachour, Nora; Clair, Emilie; Chagnon, Marie-Christine; Seralini, Gilles-Eric.

Authors affiliation: Institute of Biology, Lab. Biochemistry EA2608, University of Caen, Caen, Fr. Toxicology (2009), 262(3), pages 184-191.

Abstract: "Glyphosate-based herbicides are the most widely used across the world; they are commercialized in different formulations. Their residues are frequent pollutants in the environment. In addn., these herbicides are spread on most eaten transgenic plants, modified to tolerate high levels of these compds. in their cells. Up to 400 ppm of their residues are accepted in some feed. We exposed human liver HepG2 cells, a well-known model to study xenobiotic toxicity, to four different formulations and to glyphosate, which is usually tested alone in chronic in vivo regulatory studies. We measured cytotoxicity with three assays (Alamar Blue, MTT, ToxiLight), plus genotoxicity (comet assay), anti-estrogenic (on ER.alpha., ER.beta.) and anti-androgenic effects (on AR) using gene reporter tests. We also checked androgen to estrogen conversion by aromatase activity and mRNA. All parameters were disrupted at sub-agricultural doses with all formulations within 24 h. These effects were more dependent on the formulation than on the glyphosate concn. First, we obsd. a human cell endocrine disruption from 0.5 ppm on the androgen receptor in MDA-MB453-kb2 cells for the most active formulation (R400), then from 2 ppm the transcriptional activities on both estrogen receptors were also inhibited on HepG2. Aromatase transcription and activity were disrupted from 10 ppm. Cytotoxic effects started at 10 ppm with Alamar Blue assay (the most sensitive), and DNA damages at 5 ppm. A real cell impact of glyphosate-based herbicides residues in food, feed or in the environment has thus to be considered, and their classifications as carcinogens/mutagens/reprotoxics is discussed."

Here is a link that might be useful: link for above

Round-Up and beneficals, see the published June 2010 reviewed scientific paper link to below.

"Exposure to a glyphosate-based herbicide affects agrobiont predatory arthropod behaviour and long-term survival"

Here is a link that might be useful: link for above