# What would happen if I painted weeds with weed killer?
**URL:** https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669
**Category:** Factual Questions
**Created:** [June 7, 2011, 9:41pm UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669 "2011-06-07T21:41:40Z")
**Posts on this page:** 16
**Page:** 2
### Author:  [@elfkin477](https://boards.straightdope.com/u/elfkin477)
#### Post date: [June 8, 2011, 9:56pm UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/21 "2011-06-08T21:56:52Z")
> [@Quercus](#):
>
> Yeah, you can kill all the weeds there at any one time, but more seeds will blow in and sprout continually. I think what you really want is a good mulch, which will drastically cut down on the amount of weeds sprouting.
My flowers are pretty well mulched, but the weeds don’t seem to mind.
---
### Author:  [@Blake](https://boards.straightdope.com/u/Blake)
#### Post date: [June 9, 2011, 9:25am UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/22 "2011-06-09T09:25:28Z")
> [@SeldomSeen](#):
>
> Uptake of glyphosate (roundup-type) herbicides is through the stomata (microscopic pores in leaves and stems)..
Nope. Glyphosate is a [hydrophilic](http://croptechnology.unl.edu/pages/informationmodule.php?idinformationmodule=1056648673&topicorder=2&maxto=8&minto=1)herbicide and it [enters](http://www.ncbi.nlm.nih.gov/pubmed/11975182)the [leaf](http://www.bettersafe.com.au/papers/Sharma_Chandrasena_Singh_Glyphosate_20thAPWSS_paper%28Final%29_1.pdf)directly [through](http://www.nrrbs.com.au/chemicalsweedmaster.htm)the [cuticle](http://pubs.acs.org/doi/abs/10.1021/bk-1988-0371.ch005). Glyphosate works perfectly well on tissues with no stomata at all.
In fact I can’t think of any herbicide commonly available on the market today that depends on stomatal entry. The old nitrates and arsenicals relied on that mechanism, but they have been highly specialised herbicides for the last 40 years. I think your knowledge base is a few decades out of date.
> [@](#):
>
> ..and these do indeed close under conditions of high heat/aridity in order to prevent excessive moisture loss.
High aridity and extreme temperatures, yes. Just as I said.
> [@](#):
>
> … it is generally acknowledged that herbicide uptake is negatively effected by applying in the heat of the day.
Can I please see a a reference for his claim?
Once again, this was true of herbicides used in 1961. It hasn’t been true during my lifetime to the best of my knowledge, and that is pretty comprehensive.
> [@](#):
>
> Furthermore, while some plants do have stomata in the stems, the majority of uptake occurs in the leaves.
The majority of uptake can only occur in the leaves if the majority of the herbicide is applied to the leaves. Which is what I said above.
> [@](#):
>
> I don’t know of any literature that advises stems over leaves as an application site.
I can easily recommend some[basic literature](http://www.google.com.au/search?client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&channel=s&hl=en&source=hp&biw=1024&bih=551&q=basal+bark+herbicide&btnG=Google+Search#sclient=psy&hl=en&safe=off&client=firefox-a&hs=HIc&rls=org.mozilla:en-US%3Aofficial&channel=s&source=hp&q=basal+herbicide&aq=f&aqi=&aql=&oq=&pbx=1&bav=on.2,or.r_gc.r_pw.&fp=6f8f8e0f1f7af8ff&biw=1024&bih=551).
> [@](#):
>
> Some have claimed that application should be to the underside of the leaves, as the stomata open further there than on the top..
Once again, this was true in 1961, but I have never seen evidence that it has been true of the herbicides commonly used during my lifetime.
> [@](#):
>
> It should also be noted that little or no uptake occurs through the woody stems.
Incorrect. See the references in the last link provided.
> [@](#):
>
> Indeed, roundup can be applied with relative impunity around the trunks of trees, shrubs and vines - as long as it doesn’t get on any “green” parts it will kill herbacious weeds around the trunk but will not affect the tree or vine.
[Incorrect](http://www.caws.org.au/awc/1999/awc199912991.pdf). “The effects of basal spraying of groundsel bush with oil-soluble emulsion of glyphosate are shown in Table 2. Glyphosate emulsion adhered well to the bark and herbicidal activity was rapid, with leaf necrosis showing up within 2 weeks in some treatments.”
It is only ever safe to apply any herbicide to the trunk of large woody plants because the bark itself prevents entry to the phloem. As I already noted, for the vast majority of herbaceous or light woody plants applying herbicide to the stems is the best way to obtain a kill.
Experience has taught me that it is essential to check facts when giving advice about pesticides. Incorrect advice leads to some really upset clients.
> [@](#):
>
> Some information on effect of heat on transpiration here:
Don’t teach your grandmother to suck eggs.
Blake (PhD in plant drought physiology.) 😉
---
### Author:  [@Blake](https://boards.straightdope.com/u/Blake)
#### Post date: [June 9, 2011, 9:56am UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/23 "2011-06-09T09:56:21Z")
> [@SeldomSeen](#):
>
> T… it is generally acknowledged that herbicide uptake is negatively effected by applying in the heat of the day.
FWIW, here is are some [extension](http://www.plantmanagementnetwork.org/pub/cm/research/2005/annual/) [studies](http://appliedweeds.cfans.umn.edu/pubs/timeoday.pdf) recommending spraying during the hottest part of the day in June and July.
---
### Author:  [@chela](https://boards.straightdope.com/u/chela)
#### Post date: [June 9, 2011, 11:46am UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/24 "2011-06-09T11:46:19Z")
Joe Pye weed and ferns? I’ll take those off your hands! have you seen joe pye in bloom? gorgeous purple flowers and great for butterflies.
SOunds like you have the makings of a natural rain garden there…
---
### Author:  [@billfish678](https://boards.straightdope.com/u/billfish678)
#### Post date: [June 9, 2011, 2:18pm UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/25 "2011-06-09T14:18:37Z")
Glad someone started this thread because I’ve been meaning to do the same for awhile.
We have a nice rose garden with about 30 rose plants. Our big enemy in there is dollar weed. What weed killer would you recommend I paint on? Put on in the morning or evening? How long till safe with rain/watering? Note the garden is nearly wall to wall dollar weed right now. I live in the hot deep south (east) if that matters.
---
### Author:  [@Blake](https://boards.straightdope.com/u/Blake)
#### Post date: [June 9, 2011, 3:01pm UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/26 "2011-06-09T15:01:17Z")
> [@billfish678](#):
>
> Our big enemy in there is dollar weed. What weed killer would you recommend I paint on?
Glyphosate.
> [@](#):
>
> Put on in the morning or evening?
So long as there is no dew, it doesn’t matter much.
> [@](#):
>
> How long till safe with rain/watering?
2 hours for most formulations. Basically, once it’s dry, it’s been absorbed and rain won’t have any effect.
> [@](#):
>
> Note the garden is nearly wall to wall dollar weed right now.
Then spraying will probably be easier than wiping. I would be inclined to spray between the roses, see what dies, and then wipe any survivors if that is necessary
> [@](#):
>
> I live in the hot deep south (east) if that matters.
Not much.
---
### Author:  [@billfish678](https://boards.straightdope.com/u/billfish678)
#### Post date: [June 9, 2011, 3:10pm UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/27 "2011-06-09T15:10:14Z")
> [@Blake](#):
>
> Glyphosate.
thanks
Is that just Roundup?
---
### Author:  [@Kent\_Clark](https://boards.straightdope.com/u/Kent_Clark)
#### Post date: [June 9, 2011, 4:01pm UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/28 "2011-06-09T16:01:04Z")
Roundup was the original brand of glyphosate, there are others now.
Note that a lot of garden weed killers combine more than one active herbicide. Check the label to make sure you’re okay with whatever’s in the one you choose.
---
### Author:  [@elfkin477](https://boards.straightdope.com/u/elfkin477)
#### Post date: [June 10, 2011, 3:25am UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/29 "2011-06-10T03:25:32Z")
> [@chela](#):
>
> Joe Pye weed and ferns? I’ll take those off your hands! have you seen joe pye in bloom? gorgeous purple flowers and great for butterflies.
>
> SOunds like you have the makings of a natural rain garden there…
Most of the property has the makings for a natural rain garden (once upon a time my three-house street was a state park) and that’s fine. I just want this twenty foot stretch for something else! 😃
---
### Author:  [@CutterJohn](https://boards.straightdope.com/u/CutterJohn)
#### Post date: [June 10, 2011, 3:28pm UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/30 "2011-06-10T15:28:08Z")
I used to weed wipe in dads soybean fields before the roundup ready varieties were available. One time I didn’t notice the beans were 6 inches higher on on side of the field, and wiped about 50 yards of beans… \>\_\<
He let me use the rig after I was done with our fields. I could generally do an acre an hour. At $45-60 an acre it was great work for a 15 year old. Shame it only lasted 2 weeks a year.
---
### Author:  [@Slovel](https://boards.straightdope.com/u/Slovel)
#### Post date: [May 20, 2018, 12:39am UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/31 "2018-05-20T00:39:35Z")
My oak tree sapling are in my ivy ground cover, Does wiping poison (roundup) on oak tree sapling leaves work?
---
### Author:  [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)
#### Post date: [May 20, 2018, 2:29am UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/32 "2018-05-20T02:29:26Z")
> [@Slovel](#):
>
> My oak tree sapling are in my ivy ground cover, Does wiping poison (roundup) on oak tree sapling leaves work?
Triclopyr, triethylamine salt (Brush Killer) might be more effective against saplings. It may damage your ivy, but the ivy will grow back.
When I battle weeds, I use a mix of Round Up & Brush Killer.
---
### Author:  [@mixdenny](https://boards.straightdope.com/u/mixdenny)
#### Post date: [May 20, 2018, 5:42am UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/33 "2018-05-20T05:42:52Z")
When I bought some regular Roundup a few days ago I spotted their new product on the shelves, “Roundup Precision Gel”. It looks like a large can of deodorant and you just wipe the weeds you want to kill.
[https://www.roundup.com/en-us/products/garden-weeds/roundup-precision-gel-weed-grass-killer](https://www.roundup.com/en-us/products/garden-weeds/roundup-precision-gel-weed-grass-killer)
Dennis
---
### Author:  [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)
#### Post date: [May 20, 2018, 6:28am UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/34 "2018-05-20T06:28:15Z")
> [@mixdenny](#):
>
> When I bought some regular Roundup a few days ago I spotted their new product on the shelves, “Roundup Precision Gel”. It looks like a large can of deodorant and you just wipe the weeds you want to kill.
>
> [https://www.roundup.com/en-us/products/garden-weeds/roundup-precision-gel-weed-grass-killer](https://www.roundup.com/en-us/products/garden-weeds/roundup-precision-gel-weed-grass-killer)
>
> Dennis
I’m not really seeing the advantage of a dish full of normal Roundup and a small paintbrush. I’ve nearly wiped out the purple loosestrife in my lawn that way, and if you know purple loosestrife you know that wiping it out is the next thing to impossible.
---
### Author:  [@nightshadea](https://boards.straightdope.com/u/nightshadea)
#### Post date: [May 20, 2018, 7:20am UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/35 "2018-05-20T07:20:34Z")
How do you get rid of grass in our veg garden without killing the veggies? Mother’s day years ago my aunt got a bird feeder and her grandson hung it in the garden …well the bird feed wasn’t sterlized and we’ve had grass and other things growing that pulling can’t get rid of …
---
### Author:  [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)
#### Post date: [May 20, 2018, 6:19pm UTC](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669/36 "2018-05-20T18:19:19Z")
> [@nightshadea](#):
>
> How do you get rid of grass in our veg garden without killing the veggies? Mother’s day years ago my aunt got a bird feeder and her grandson hung it in the garden …well the bird feed wasn’t sterlized and we’ve had grass and other things growing that pulling can’t get rid of …
Bake your birdseed 30 minutes at 300 degrees or microwave it for 5 minutes. This will prevent the seeds from germinating in your flower beds.
[Previous page](https://boards.straightdope.com/t/what-would-happen-if-i-painted-weeds-with-weed-killer/584669.md?page=1)