How to remove visual "plume"?

Hi.

My PC specs:
CPU: i7-4500U 2.4GHz

RAM: 8 GB

Nvidia GeForce GT 740M

If it’s not effects - what is it?

I found, that the same effect will be show in UEs “Third Person” example, if I will add to it landscape with grass material.

Example - landscape without mat - looks good: UE4Editor 2015 09 06 14 15 41 94 - YouTube

And example with “plume” - when landscape has grass mat - UE4Editor 2015 09 06 14 16 51 77 - YouTube

If it’s not defaults and my PC is weak - how to remove this with my current PC specs?