How to kill echinops?

I am playing The Witcher at maximum difficulty and it is indeed difficult as it describes, even more.

At the moment I have some (many) problems killing Echinops in Vizima swamps. Do you have some suggestions how to fight them?

They are sensitive to fire, using Igni to ignite them works pretty well. You can use Argentia oil on your silver sword if you have the material to increase your damage.

Be careful to never engage more than one of them, they can't move so you just need to position yourself well. There is also a named archespore in the swamp (Coccacidium) which can easily kill you if you're careless. It looks very similar to an echinops and can spawn in several locations. You'll get a trophy for killing it. You might have to avoid that one until you leveled a bit if you're having problems, but you should be able to kill the normal echinops.

Hm using silver sword should be pretty obvious,the other thing is that they are weak to fire(incineration).

Other than that it is all on you skill and preparation...hit and run,potions...

They are the strongest enemy and the more troublesome in chapter 2. My advice is to run and to not engage them: they are deadly even at normal difficulty. However they'll become pieces of cake by the time you'll reach chapter 3. If you want to fight them then igni and any form of protecyion are your best friends.