Related Rule
Practice Relating to Rule 54. Attacks against Objects Indispensable to the Survival of the Civilian Population
Section C. Attacks in case of military necessity
Switzerland’s Basic Military Manual (1987) states: “It is prohibited to employ scorched earth tactics.” 
Switzerland, Lois et coutumes de la guerre (Extrait et commentaire), Règlement 51.7/II f, Armée Suisse, 1987, Article 35, commentary.
Switzerland’s Regulation on Legal Bases for Conduct during an Engagement (2005) states:
12.2 Principle of military necessity
160 This principle allows all measures that are not prohibited by the law of armed conflict and that are necessary to accomplish the mission. However, military necessity may not be invoked to justify disrespect for the international law of armed conflict, unless this is expressly provided for by the rules.
161 Thus, for example, a party to the conflict may refrain from protecting objects indispensable to the survival of the civilian population if it does so to repel an enemy invasion, as long as it is necessary from a military point of view (see Art. 54, para. 5 of Additional Protocol I). 
Switzerland, Bases légales du comportement à l’engagement (BCE), Règlement 51.007/IVf, Swiss Army, issued based on Article 10 of the Ordinance on the Organization of the Federal Department for Defence, Civil Protection and Sports of 7 March 2003, entry into force on 1 July 2005, §§ 160–161. The German language version of the first sentence of § 161 notes: “… as long as it is imperatively necessary [“zwingend erforderlich”] from a military point of view …”.