@CaTBaT Because you are creating an object as a MenuItem, and adding that Item to menu onTick basis.
void onTick(object sender, EventArgs e)
{
//
if (modMenuPool != null) modMenuPool.ProcessMenus();
//
if (INV_Weed == true && Take_weed >0)
{
UIMenuItem Weed = new UIMenuItem("Травка " + Take_weed);
mainMenu.AddItem(Weed);
INV_Weed = false; }
return;
}