how r weedicides weed specific??

[rosalin]

i read sumwhre that synthetic auxins such as 2,4- Dichlorophenoxyacetic acid (or 2,4-D) are often used as weedicides (because auxins in excess stimulate the production of ethylene which causes leaf fall and the plant begins to die).

how is it that they only affect the weeds and not the crop?

(is it because weeds have high growth rate? )

[SororSaudade]

maybe, as weeds are smaller, they are easily afected by smaller amounts of those auxins (though i'm not sure).

[rosalin]

what ? i don't understand. i was thinking 'bout the HIGH growth rate of weeds that would lead to a higher conc. of growth hormones like auxins as compared to the crop.

[SororSaudade]

well, I can't understand your point either

I've never heard of auxins as "weedicides", but what I ment is that smaller plants could be less tolerant to certain amounts of auxins, but yet this may be a stupid answer, I don't know.

If you find the right answer please let me know

[sachin]

weedicides are made according to weed's physiology so that it will harm the weekest point of weed's physiology which is strenght of our important plant's physiology...

[rosalin]

I've never heard of auxins as "weedicides", but what I ment is that smaller plants could be less tolerant to certain amounts of auxins, but yet this may be a stupid answer, I don't know.

ah! i see ur point now but i'm not so sure.
i'm trying to find out.

so that it will harm the weekest point of weed's physiology which is strenght of our important plant's physiology...

could u please elaborate?

[mith]

High growth rate...so if it's sped up I'm guessing it ages faster...

[rosalin]

i found something in wikipedia 'bot this:

Some synthetic auxins such as 2,4-D and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) can be used as herbicides.Broad-leaf plants (dicots) such as dandelions are much more susceptible to auxins than narrow-leaf plants (monocots) like grass and cereal crops.

http://en.wikipedia.org/wiki/Auxin

i guess this more or less clarifies things a bit.

[MrMistery]

the clarification is: monocots are much better at rapidly inactivating excess auxins than eudicots. Since crop plants are monocots, they can resist the auxins while weeds(mostly eudicots) die from excess hormones. Nothing to do with growth rates really..

[SororSaudade]

nice to know that

Thanks for sharing the right answer!