Related Rule
Germany
Practice Relating to Rule 72. Poison and Poisoned Weapons
Germany’s Military Manual (1992) states: “It is prohibited to employ poison and poisoned weapons.” 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten KonfliktenHandbuch, August 1992, § 426.
The manual adds: “The prohibition also applies to the toxic contamination of water supply installations and foodstuffs … for military purposes.” 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten KonfliktenHandbuch, August 1992, § 434.
Germany’s Law Introducing the International Crimes Code (2002) punishes anyone who, in connection with an international or a non-international armed conflict, “employs poison or poisoned weapons”. 
Germany, Law Introducing the International Crimes Code, 2002, Article 1, § 12(1)(1).