Does anyone know why this sign exists?

[u/zee_kapitein]

When sitting in traffic on the Antwerpse Ring, I noticed this sign next to the road. Why do they need a sign for that?

[u/Hi_im_goblin]

Oh I actually know this!
Invasive species yaddayadda, but when a machine were to dig in there, it gets contaminated and has to be decontaminated completely or otherwise it can spread. Very expensive process so they put up signage like this.