Related Rule
France
Practice Relating to Rule 72. Poison and Poisoned Weapons
France’s LOAC Summary Note (1992) states that it is prohibited to use poisoned weapons. 
France, Fiche de Synthèse sur les Règles Applicables dans les Conflits Armés, Note No. 432/DEF/EMA/OL.2/NP, Général de Corps d’Armée Voinot (pour l’Amiral Lanxade, Chef d’Etat-major des Armées), 1992, § 4.6.
France’s LOAC Teaching Note (2000) includes poison in the list of weapons that “are totally prohibited by the law of armed conflict” “owing to their inhuman nature or to their excessive traumatic effect”. 
France, Fiche didactique relative au droit des conflits armés, Directive of the Ministry of Defence, 4 January 2000, annexed to the Directive No. 147 of the Ministry of Defence of 4 January 2000, p. 6.
France’s LOAC Manual (2001) incorporates the content of Article 23(a) of the 1907 Hague Regulations. 
France, Manuel de droit des conflits armés, Ministère de la Défense, Direction des Affaires Juridiques, Sous-Direction du droit international humanitaire et du droit européen, Bureau du droit des conflits armés, 2001, p. 97.
It also includes poison in the list of weapons that “are totally prohibited by the law of armed conflicts” “owing to their inhuman nature or to their excessive traumatic effect”. 
France, Manuel de droit des conflits armés, Ministère de la Défense, Direction des Affaires Juridiques, Sous-Direction du droit international humanitaire et du droit européen, Bureau du droit des conflits armés, 2001, p. 54.
France’s Penal Code (1992), as amended in 2010, states in its section on war crimes related to international armed conflict: “[The following offences] are punishable by life imprisonment: … [u]sing poison and poisoned weapons”. 
France, Penal Code, 1992, as amended in 2010, Article 461-23.