I can't remember if this discussion is going on on Tweeters or PNW-natives,
so I'll post it to both.

I want to contribute some thoughtful observations and advice on using
Roundup, as I'm not sure the discussion so far has been very helpful to
those debating whether to use it or not. I have some experience with this
that may be useful, as I am 1) a professional environmental scientist who
works on cleaning up and restoring rivers and wetlands, 2) a chemist who
evaluates the toxicity and fate of chemicals in the environment as part of
my job, and 3) someone who has used and closely observed the effects of
Roundup on my property for the last 5 years.

I will start by providing a summary opinion, based on what experience and
knowledge I and my co-workers have, then follow it up with supporting
observations and tips for when and when not to use it, and how to use it as
safely as possible.

The summary opinion is this: Roundup is the ONLY relatively safe chemical
that is effective for use in the Pacific NW against highly invasive species,
such as Himalayan blackberry, scotchbroom, reed canary grass, and morning
glory. The key terms in here are "relatively safe" and "effective against
invasives".

In my experience, this summary view is widely shared by professionals and
restoration ecologists. Roundup (in various formulations) is often used as
the first step in wetlands and prairie restoration projects, because without
it, in many cases, any native planting that is done is quickly overwhelmed
by invasive species. Also because it does NOT kill the soil, birds,
animals, etc. Essentially, it is the lesser of two evils. I do not dispute
that it may be toxic to insects in laboratory tests, however, the effect is
TEMPORARY, limited to the area of application and not likely to have any
long-term impact on the overall insect population. It is most appropriately
used as the first step in the process, when ground is being cleared of weeds
and invasive species to allow newly planted native plants time and space to
take hold. Restoration professionals are some of the most environmentally
conservative people I know, and would not be likely to use such a product if
it had long-lasting effects.

Lines of evidence I personally use to make decisions about the relative
safety of glyphosate or other chemicals: 1) chemical structure and
properties, 2) existing laboratory tests, 3) professional experience, 4)
personal experience.

1) From a chemist's point of view, there would be no reason (or plausible
mechanism) for glyphosate to persist in the environment. It has no chlorine
or other chemical constituents or structures that would allow it to remain
in the soil or water without breaking down. In fact, it is designed
specifically to break down within a few days. It is not stable upon
exposure to air or water. It works by spraying it on green leafy surfaces,
which absorb the chemical and send it to the roots, where it kills the plant
internally. It cannot be absorbed by the plant from the soil (because it is
not stable in water), it must be sprayed directly on the plant. Not only
that, it has to be sprayed on the green leafy part of the plant. For
example, it has no effect on horsetails, which do not have the right plant
structures to absorb Roundup. It has a pretty specific mode of action,
which makes it less likely to cause unintended harm.

2) Roundup has undergone extensive testing during the licensing process
which demonstrates the above properties. This to me is simply confirmation
of what any chemist can see by looking at the chemical structure - it's not
a persistent chemical. This is not to say that government testing is
infallible, which is obviously not the case. It's just another confirmatory
line of evidence.

3) As noted above, we use the chemical in wetlands and other restoration
projects, when, and only when, it is necessary for the success of the
project. We have not observed planting failures, fish kills, bird kills or
other adverse effects following careful application of roundup as the first
step in these projects.

4) I have used Roundup on my property to control Himalayan blackberry,
Scotchbroom, and morning glory, in preparation for replanting with native
species. I have not observed any adverse effects on other plants or
wildlife, or had any problem replanting those areas later. In several
cases, immediately after removing large stands of blackberries using
Roundup, grasses, peas, and yes, morning glory have immediately popped up
once the overstory was removed.

As far as claims by arborists or nurserymen that it has made the ground
unsuitable for planting, I find this hard to understand. I would never
discount personal experience, but this is just not consistent with my
personal experience or other facts about how this chemical works. I might
offer two possible explanations for such an observation:

1) If soil is saturated by Roundup (not at all the recommended method of
application, see later in this post), it may be possible to kill
microorganisms that are needed for successful growth of certain native
shrubs and trees. It is important to recognize that it is not that there is
any "poison" left in the soil a year later, however, the soil may have been
sterilized. I'm not really sure that this could happen, since it is my
understanding that Roundup only works on leafy plants, but it seems
possible. The remedy in this case would be to work in some native soil to
replace the microorganisms, as is often recommended anyway, since much of
the topsoil and other materials you can order for your garden are also
sterile.

2) People may be having planting failures and incorrectly attributing it to
the previous application of Roundup. Plants fail all the time, even in the
best planned restoration projects. There are many causes of failure, and
without a controlled experiment, it is not clear to me how a person would
know the specific cause. There may be an equal number of failures with or
without previous application of Roundup, but in cases where Roundup has been
applied, people might assume that was the cause without actually knowing.

Working in this field, it is my experience that it is often difficult for
the public to sort out conflicting claims of harm or safety by chemicals.
One thing that is often observed is that people are more distrustful of
manufactured chemicals and things they don't use very often than commonly
used "natural" products that are perceived as safe. For example, people
distrust Roundup (not unreasonably) because it was developed by a chemical
company as an herbicide. Yet knowing what I do about it, I would say it's
much safer for the environment when used properly than application of lawn
fertilizers (which may be natural products). Unlike Roundup, lawn
fertilizers are designed to be soluble in water so that they can be taken up
by plant roots. Unfortunately, this means that they are carried by water
into aquifers (where they are harmful to those drinking the water) and
streams/rivers/wetlands, where they contribute to excess nutrients and
greatly change the structure of the ecosystem. Yet I think most people
would assume that fertilizers are safer than herbicides. The point here is
that each chemical must be judged on its own merits and effects, and the
safety of any chemical or natural product for the ecosystem depends greatly
on how it is used.

Having said that, here are some tips for using, or not using, Roundup:

1) Use this product only when nothing else will work. By this I mean for
control of invasive species that cannot reasonably be eliminated through
weed pulling and "Safer" type products. What can reasonably be eliminated
by you is a personal decision, for example, some people have success with
blackberries by continually cutting them down year after year. You may or
may not have the time or strength to do this. Some plants, such as morning
glory, purple loosestrife, and reed canary grass, may not be possible to
permanently eliminate by weeding or pulling, since they regrow from even
small pieces left behind in the soil.

2) Roundup is best used as the first step in clearing an area of weeds prior
to native planting or gardening with desired species. It is dangerous to
use once an area is planted because it is hard to apply without damaging
nearby plants. If invasive weeds are thoroughly ensconced in an area, you
may need more than one application of Roundup before planting. For example,
a technique that works well is to use it once late in the summer when it's
hot and dry. This will take care of most of it. Then reapply to anything
that grows back the following spring/early summer, when the weeds are
actively growing. Plant the following fall, when you are sure the weeds are
gone and when you have good weather for planting.

3) Apply roundup on a calm day, so that overspray into other areas is not a
problem. Roundup works best when applied during hot, sunny weather, as it
interferes with photosynthesis. Do not apply Roundup when plants are wet
from dew or when it is likely to rain in the next day or two. This is
because, as mentioned above, Roundup is not stable in water and may not be
effective under these conditions - it can be washed off plant leaves before
it has a chance to absorb.

4) If you need to apply roundup to control morning glory, blackberries or
other things coming up in already planted areas, there are ways to apply it
that protect nearby plants. One good way is the paintbrush method: mix up
Roundup in a bucket, carefully disentangle the morning glory (or whatever)
from your plants, and paint the leaves with Roundup, being careful that the
painted leaves do not spring back and get Roundup on your other plants.

5. Use the proper formulation and give it time to work. Use regular Roundup
for morning glory, grasses, dandelions, and other smaller plants, and
stronger formulations for brushy plants such as blackberries and
scotchbroom. Do not use the stronger formulation on smaller plants, because
it may kill the top growth too early and not allow it to travel to the
roots. There is also a particular formulation for wetlands or other areas
near water. When using on blackberries or scotchbroom, you will not see the
effects right away. It takes time for the chemical to absorb, travel to the
roots, and kill off a plant as strong as these. It usually takes about a
month for these plants, and it's important to let them sit during this time.
Don't cut them down or reapply the Roundup because you are not seeing
results right away.

6. Contrary to popular advice, do not cut the plant down, then apply Roundup
to the stem. Roundup works best on the leafy parts, and the more of the
leaves you can coat with it, especially during the growing season, the
better it will work. Be sure to get both tops and bottoms of leaves if
possible.

I hope this post has been helpful - Teresa Michelsen