Why doesn't roundup work on dandelions?? (flower, lawn, grow, grass)

[mountainrose]

We have about three acres of grass that's getting a lot of dandelions. We don't want to use a toxic broad leaf poison on the whole three acres, so have tried to spot kill the dandelions with Roundup. We did it on a sunny day, no wind. They are not dead, and are still producing flowers. Is Roundup not strong enough for dandelions? We also tried vinegar first, and that didn't work either. Any ideas?
Thanks

[Pitt Chick]

I have successfully used RoundUp on dandelions over the years.

Did you dilute it properly?

[jacqueg]

Did you ever consider letting the dandys be? They are a great early-spring food source for bumblebees.

Also, if you have *a lot* of dandelions, you lawn may have an underlying problem that favors weeds over grass. It may be that if you addressed these issues you would have fewer dandelions and would not be so worried by their presence.

http://www.beyondpesticides.org/pest...ic%20Lawns.pdf

Organic Lawn Care For the Cheap and Lazy

[TinaMcG]

Originally Posted by mountainrose

We have about three acres of grass that's getting a lot of dandelions. We don't want to use a toxic broad leaf poison on the whole three acres, so have tried to spot kill the dandelions with Roundup. We did it on a sunny day, no wind. They are not dead, and are still producing flowers. Is Roundup not strong enough for dandelions? We also tried vinegar first, and that didn't work either. Any ideas?
Thanks

Roundup works fine on dandelions, but they are best treated in the fall, and especially when they're not flowering for best results. It can also take up to ten days to kill them. The best conditions for applying Roundup don't necessarily include a sunny day. THIS is the best set of conditions:

1. A cool or cold morning
2. A good coating of dew
3. No wind or very light winds
4. Forecast or warmer and sunnier temperatures later in the day

The reason this is ideal is that the chemical can only be taken up by the plant as long as it is wet, and the dew ensures the foliage stays wet as long as possible. Once Roundup dries on the foliage, it doesn't do anything. It just breaks down in sunlight, but it's ineffective for killing the plant if it's just sitting on the leaves.

When temps are cool or cold (frost is even better), the plant is defensive and is working hard to take in as much moisture and nutrients as possible, to store in its roots. The Roundup goes along for the ride and ends up in the roots a lot faster on a cool, dewy morning.

Then later in the day when temps warm up, the plant begins to release food (and Roundup) from the roots and the plant begins to grow rapidly -- and die at the same time.

I treated a lot of weeds last Friday under those conditions, using some lawn weed killer and also some Roundup in the flower beds. Everything I wanted to kill off is pretty much dead now, which is a very fast kill.


Vinegar will never work on dandelions because it doesn't kill the root. The weed just grows back.

[Hemlock140]

The other problem in eliminating them is that the seeds blow over from the neighbors and keep replanting in your lawn. The best thing is to pull them up by the roots, but with a big lawn there are granular broadleaf killers that you can apply with a spreader just before a rain, and it will kill them in a few days. some of the flowers, however, can still go to seed after the plant is dead. They really need to be picked off and thrown in the garbage.

[villageidiot1]

Originally Posted by Hemlock140

The other problem in eliminating them is that the seeds blow over from the neighbors and keep replanting in your lawn. The best thing is to pull them up by the roots, but with a big lawn there are granular broadleaf killers that you can apply with a spreader just before a rain, and it will kill them in a few days. some of the flowers, however, can still go to seed after the plant is dead. They really need to be picked off and thrown in the garbage.

If you apply any broadleaf weed killer before a rain it will just wash of the weeds and not kill them. See TinaMcG's response above. I prefer to use a liquid weed killer that I apply with a sprayer. I apply either early in the morning or after a rain. The sprayer allows me to apply it only where needed. Since I do this a couple times every year, I don't have many dandelions and other broadleaf weeds. I usually only have to mix up a couple of gallons for a large yard.

[VJDAY81445]

my neighbor just sprayed his entire lawn with a mild 2 4D PRODUCT ( 3 YEARS AGO) and has had no problem since.

[VJDAY81445]

Originally Posted by villageidiot1

If you apply any broadleaf weed killer before a rain it will just wash of the weeds and not kill them. See TinaMcG's response above. I prefer to use a liquid weed killer that I apply with a sprayer. I apply either early in the morning or after a rain. The sprayer allows me to apply it only where needed. Since I do this a couple times every year, I don't have many dandelions and other broadleaf weeds. I usually only have to mix up a couple of gallons for a large yard.

FALSE...............if it is a granule it needs water in order to work. Dry granules and no rain isn't going to dissolve the granules.

[villageidiot1]

Originally Posted by VJDAY81445

FALSE...............if it is a granule it needs water in order to work. Dry granules and no rain isn't going to dissolve the granules.

FALSE...............if it is a granule, it needs to stick to a wet surface to work. Spreading the granules on dry weeds will not give the granules anything to stick to. Rain after application will just further wash the granules into the soil where they are not effective.

[mountainrose]

Thanks for all this great feedback and information!

We keep all our pastures organic and there's plenty of clover and such for the bees.
But my husband likes the grass around the house to not look like pasture, so we are trying to
Find the least toxic way to keep the dandelions down.

After reading all these comments, I think we'll try spot shooting each dandelion again with Roundup on a damp cool morning, and make sure we got the dilution right. Some we thought didn't die, did take a few days and now are dying.

Also, my husband just bought a torch thing which is totally non toxic and you burn each dandelion which supposedly gets down to its roots. It also supposedly works on thistle in our pastures.

Anyone have experience with using a torch?