zelkova root problem RKN ?

Hi, my Zelkova has RKN,i think, how do i treat it ?
whats causing this ,& is it a problem for the trees growth ?
Thanks.

...it's rhizobium ....

nice and good for tree !!!(symbiosis)
fix atmospheric nitrogen into a form that plants can use

current with ulmacées.

You'll see nodules like that on many species that host nitrogen fixing microorganisms, Elaeagnus is one species where the growths are quite pronounced as well.
-Jay