I am unable to see the wasps nests due to the tall dense weeds. How can I get rid of them?
Both my neighbor and I, betweeen us, have so far dealt with seven wasp nests this fall.
Where are you located? If in cold climate, the situation should resolve itself when the frost hits. The queen will move on. If in the country, can you burn the patch (if you are clearing the weeds, anyway)?
Depending on the species, it's likely that the nest is among some rocks or pieces of old wood. Can you see those in the weeds, or are they all over the place?
You must have a general idea where the nest is. Try to follow some of the insects as they return home, even if just with your eyes. On a cool evening, you could start cutting a path toward the nest so that you can get a clear shot with a can of wasp spray (which reach a considerable distance).
Also keep in mind that you could have several nests. You could corner yourself. I had assumed a certain rivalry among separate colonies, but my neighbor had three small nests within two feet of each other. Someone fixing my garage roof found two sizable ones (and got stung while removing one when he didn't notice the other one).
If all fails, hiring a pest control company isn't all that expensive. Some of those people are fearless. I saw one guy go into a crawlspace under a deck without a protective suit to get at a nest. Gave me the creeps.
I don't know where you live but these hives can be dangerous to someone who doesn't know what he's doing. We have huge yellow jacket nests/hives that are underground or hidden in tree roots. When disturbed they attack with a fury and people have died as a result of the 1,000's of stings.
Call an expert.
The first person I ever witnessed die had blundered into a bald faced hornet bag nest in some short scrub.
I was only about 6 years old.