Reply Wed 6 May, 2009 06:00 pm
Why doesn't weed-killer herbicides kill lawn grass too? How could grass be more resistant to the chemicals than weeds?

Just curious -- the question arose while watching a TV commercial advertising weed killer that is harmless to grass.
  • Topic Stats
  • Top Replies
  • Link to this Topic
Type: Question • Score: 5 • Views: 6,254 • Replies: 5
No top replies

 
dyslexia
 
  2  
Reply Wed 6 May, 2009 06:56 pm
@easyasabc,
the basic idea is that such products as weedbegone targets broadleaf weeds and not narrow leaf such as lawn grass.
0 Replies
 
Green Witch
 
  1  
Reply Wed 6 May, 2009 07:36 pm
@easyasabc,
All plants are not the same. It is possible to poison one species and not another. Plants are many different species.
0 Replies
 
rosborne979
 
  2  
Reply Wed 6 May, 2009 07:36 pm
@easyasabc,
easyasabc wrote:

Why doesn't weed-killer herbicides kill lawn grass too? How could grass be more resistant to the chemicals than weeds?

Just curious -- the question arose while watching a TV commercial advertising weed killer that is harmless to grass.

This was a cool question. Thanks.

Grasses and Broadleaf weeds are both angiosperms (flowing plants), however, they are in two different families. The grasses are called Monocots and the Broadleaf weeds are called Dicots.

There are morphological differences between the Monocots and Dicots which cause them to react differently to certain herbicides. The primary broadleaf selective herbicide in use today is 2,4-D.
Quote:
Broadleaf weed killers are selective herbicides that work in lawns by targeting dicots that are actively growing while not harming the monocots such as lawn grass. The most common type of broadleaf weed killer is 2,4-D also known as Trimec.
2,4-D is an auxin or plant hormone that, when applied to the leaf area, simply confuses the plant to death. Since auxin is the hormone that makes plants grow, when it's sprayed over the entire plant, the plant doesn't know which way to grow, becomes deformed, then dies.

From what I can tell the primary characteristic in Dicots which makes them more susceptible to Trimec has to do with the meristem.
Quote:
In monocot stems, the vascular tissues " the phloem and xylem " are in bundles scattered throughout the stem, and they typically lack a vascular cambium. In dicot stems, the phloem and xylem are in rings around each other. They nearly always have cambium. Despite a pine's stem structure resemblance to dicots, it is neither a dicot nor a monocot. A pine is a conifer, which is not a flowering plant at all.

Partly as a consequence of the arrangement of the vascular tissue, in monocots, there is very little new phloem and xylem added to the stem. Thus, monocot stems do not grow significantly thicker each year. Any change in thickness is due to the cells getting slightly larger. On the other hand, dicot stems can add new vascular tissue and thus grow thicker with time. Most flowering trees are dicots.

I haven't been able to determine the specific metabolic function in the Dicot which makes it unique from the Monocot, but I think it has something to do with the way the meristem grows and possibly the rate of growth.
Wiki wrote:
Mechanism of herbicide action

2,4-D is a synthetic auxin, which is a class of plant growth regulators. It is absorbed through the leaves and is translocated to the meristems of the plant. Uncontrolled, unsustainable growth ensues causing stem curl-over, leaf withering, and eventual plant death. 2,4-D is typically applied as an amine salt, but more potent ester versions exist as well.
farmerman
 
  1  
Reply Thu 7 May, 2009 05:44 am
@rosborne979,
auxins are a cool class of ag chemical. In lower doses the chemical will control rooting and fruit setting (Indolacetic acid=+ROOTONE is actually an auxin). In more concentrated forms (like 24D nd 245 T=Agent ORANGE), the chem will cause the plant to grow uncontrollably and(heres the secret), The plant begins to exude ETHYLENE, which makes the plant mature quickly and then die. So the plant goes into a growth spurt, then begins aging and dies.

Other ones like Glyphosates(ROUNDUP etc) , are still not well understood except that they mess with the main respiration chemicals (called PEP's) and they cause the plant to fail in respiration and transpiration.

farmerman
 
  1  
Reply Thu 7 May, 2009 05:56 am
@farmerman,
Im not sure about this but maybe the position of the meristematic zone in monocots (grasses) is the important factor. Grasses are Root Apical Meristematics and dicots are Shoot apical meristematics. A root apical meritem (RAM) is always sloughing off and is evolved to accomodate fierce ground level grazing by herbivores. The growth center is deep within the apical meristem which is in the plant crown which is underground, whereas the SQAM's are at the plant stems and branches.

Im not wed to this but I could look it up later when I get back.
0 Replies
 
 

Related Topics

New Propulsion, the "EM Drive" - Question by TomTomBinks
The Science Thread - Discussion by Wilso
Why do people deny evolution? - Question by JimmyJ
Are we alone in the universe? - Discussion by Jpsy
Fake Science Journals - Discussion by rosborne979
Controvertial "Proof" of Multiverse! - Discussion by littlek
 
  1. Forums
  2. » Tough as a weed!
Copyright © 2019 MadLab, LLC :: Terms of Service :: Privacy Policy :: Page generated in 0.03 seconds on 05/20/2019 at 02:55:28