Were you using it when we had all that rain at the beginning of the month? Perhaps it washed off before being absorbed.

Nope. It had rained two days before, and the grass was dry. Wish I could figure this all out.

I use 'Weed B Gone' and it works. If the weeds are large it may take up to a week to see wilting but everything I spray dies.

BTW, I always use the concentrate and mix it a little stronger than the directions. As long as it's had time to dry, rain doesn't affect the results.

Dandelions require repeated applications of a broad-leaf weed killer.

You must repeat because the plant has a fleshy root which will survive to grow more leaves. With repeated applications (each time the plant regrows), the root is eventually starved and the dandelion is gone.

Or you could just "settle" for a lawn full of flowers instead of an Astroturf look and stop exposing yourself, children, pets and wildlife to carcinogenic and mutagenic chemicals.

Good question.

It should work.

Many weed killers will have 3 herbicides on the label as active ingredients.

Like the Weed B Gone, mentioned, etc..

It should not take repeat spray to at least see initial damage.

In fact, if you spray at 75% label rate, you may get the old ones too - fully. A slow kill is a better kill many times.

I've sprayed country clubs several times - hundreds of acres - and the results should be better than what you indicated.

What's the weak link in the chain?

Is there any possibility that you mixed it wrong? You're 100% sure that it's concentrated?

Is there just 1 active ingredient on the label?

Are the leaves at least shriveling? A good application should show slight twisting of foliage within a few hours; or at least the same day.

It may take 2 to 3 weeks for the complete kill to occur.

Yeah, what bboy said :-) Or invest in a good long-handled, taproot weed tool and remove them manually. Nice exercise, gets you in tune with your garden, can put you in a very Zen-like state and zero chance of additional pollution of our fragile environment.

Chemical lawn herbicides should be avoided whenever possible.

Yes, weeds are definitely preferable to herbicides.....and lawns...