Australia
Practice Relating to the Use of Prohibited Weapons
Australia’s Commanders’ Guide (1994) provides: “Some weapons and weapons systems are totally prohibited.” 
Australia, Law of Armed Conflict, Commanders’ Guide, Australian Defence Force Publication, Operations Series, ADFP 37 Supplement 1 – Interim Edition, 7 March 1994, § 304.
The Guide further states: “The following examples constitute grave breaches or serious war crimes likely to warrant institution of criminal proceedings: … using certain unlawful weapons and ammunition such as poison.” 
Australia, Law of Armed Conflict, Commanders’ Guide, Australian Defence Force Publication, Operations Series, ADFP 37 Supplement 1 – Interim Edition, 7 March 1994, § 1305(p).
Australia’s Defence Force Manual (1994) provides that “prohibited weapons” is one of the categories into which the limitations on the use of weapons fall. 
Australia, Manual on Law of Armed Conflict, Australian Defence Force Publication, Operations Series, ADFP 37 – Interim Edition, 1994, § 401.
The manual further states: “The following examples constitute grave breaches or serious war crimes likely to warrant institution of criminal proceedings: … using certain unlawful weapons and ammunition such as poison.” 
Australia, Manual on Law of Armed Conflict, Australian Defence Force Publication, Operations Series, ADFP 37 – Interim Edition, 1994, § 1315(p).
Australia’s LOAC Manual (2006) states:
Limitations on the use of weapons fall into two broad categories, namely:
- prohibited weapons, and
- the illegal use of lawful weapons. 
Australia, The Manual of the Law of Armed Conflict, Australian Defence Doctrine Publication 06.4, Australian Defence Headquarters, 11 May 2006, § 4.1.
The manual further states:
Some weapons and weapons systems are totally prohibited. These blanket prohibitions, which may be traced to treaty or customary international law, are justified on the grounds that the weapons in question are either indiscriminate in their effect or cause unnecessary suffering. 
Australia, The Manual of the Law of Armed Conflict, Australian Defence Doctrine Publication 06.4, Australian Defence Headquarters, 11 May 2006, § 4.4.
The LOAC Manual (2006) replaces both the Defence Force Manual (1994) and the Commanders’ Guide (1994).