The description of the enemy camps as fungus growths suggests that they’re quick-spreading and ugly. This is a direct contrast to the tower of Minas Tirith, which is ancient, beautiful, and was built by master craftsmen over many years. Where the enemy takes a quick and crude route to success, Gondor’s approach is more traditional, relying on the strength of men and their individual skills. It’s unclear at this point which approach will prove stronger, but Mordor’s inhumane methods, including firing human heads into the city, proves they can induce despair for Gondor’s troops.