Rule 76. The use of herbicides as a method of warfare is prohibited if they:
a) are of a nature to be prohibited chemical weapons;
b) are of a nature to be prohibited biological weapons;
c) are aimed at vegetation that is not a military objective;
d) would cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which may be expected to be excessive in relation to the concrete and direct military advantage anticipated; or
e) would cause widespread, long-term and severe damage to the natural environment.
State practice establishes this rule as a norm of customary international law applicable in both international and non-international armed conflicts.
Before the adoption of the Chemical Weapons Convention, there was disagreement as to whether herbicides were prohibited under the Geneva Gas Protocol. In 1969, for example, 80 States voted in favour of a UN General Assembly resolution indicating that the use of herbicides would be contrary to “generally recognized rules of international law, as embodied in the Geneva Gas Protocol”, although the 3 negative votes and 36 abstentions show that this was not a universally held view.[1] In particular, several States considered that the use of herbicides and defoliants was not prohibited under the Geneva Gas Protocol.[2]
The experience of the Vietnam War, however, revealed the potentially long-term serious effects of herbicides on human health. This use was condemned by other States.[3] Developments in international law since then have attached increased importance to the protection of the environment. It is clear that any use of herbicides in warfare would be controversial, in particular in the light of the clear trend in favour of protecting the environment against deliberate damage. Environmental considerations reportedly led the United States to end its herbicidal programme.[4]
It is relevant in this respect that the Final Declaration of the Second Review Conference of the Parties to the ENMOD Convention reaffirmed that the military and any other hostile use of herbicides as an environmental modification technique is a prohibited method of warfare “if such a use of herbicides upsets the ecological balance of a region, thus causing widespread, long-lasting or severe effects as the means of destruction, damage or injury to another State Party”.[5] In a resolution adopted without a vote, the UN General Assembly noted with satisfaction this reaffirmation.[6] Some States welcomed it as a confirmation of the ban on the use of herbicides as a method of warfare.[7] These and other considerations led the negotiators of the Chemical Weapons Convention to recognize “the prohibition, embodied in pertinent agreements and relevant principles of international law, of the use of herbicides as a method of warfare”.[8]
The Chemical Weapons Convention does not, however, define what use would qualify as a method of warfare. The United States, for example, has stated that it reserves the right to use herbicides “for control of vegetation within U.S. bases and installations or around their immediate defensive perimeters”.[9]
It is clear, however, that the use of herbicides in armed conflict as a method of warfare would violate the general prohibition of the use of chemical weapons if they are of a nature to harm humans or animals (see Rule 74). In addition, the use of herbicides consisting of, or containing, biological agents would violate the Biological Weapons Convention in that it prohibits the use of all biological agents that are not for prophylactic, protective or other peaceful purposes (see Rule 73).
In addition, attacks on vegetation by herbicides would violate the general rules on the conduct of hostilities if the vegetation is not a military objective (see Rule 7), if the attack causes excessive incidental civilian losses or damage to civilian objects (see Rule 14) or if the attack may be expected to cause widespread, long-term and severe damage to the natural environment (see Rule 45).
Other rules of international humanitarian law that may be relevant to the use of herbicides are the prohibition of starvation as a method of warfare (see Rule 53) and the prohibition on attacking objects indispensable to the survival of the civilian population (see Rule 54), in case herbicides would be used against crops.
Although there is less specific practice concerning the use of herbicides in non-international armed conflicts, the specific limitations on or prohibitions of the use of herbicides contained in this rule are general rules that apply also to non-international armed conflicts.
In addition, recent allegations of possible use in Chechnya were denied by the Russian government.[10] This shows that there is a legitimate expectation on the part of States that herbicides must not be used in a way that would violate other rules applicable in any type of armed conflict.
[1] UN General Assembly, Res. 2603 A (XXIV) (cited in Vol. II, Ch. 24, § 630).
[2] See, e.g., the statements of Australia (ibid., § 615), United Kingdom (ibid., § 624) and United States (ibid., §§ 625–626).
[3] See, e.g., the statements of China (ibid., § 617) and Hungary (ibid., § 619); see also the statement of China (ibid., § 618).
[4] See William A. Buckingham, Operation Ranch Hand: The Air Force and Herbicides in Southeast Asia, 1961-1971 (ibid., § 628).
[5] Second Review Conference of the Parties to the ENMOD Convention, Final Declaration (ibid., § 633).
[6] UN General Assembly, Res. 47/52 E (ibid., § 631).
[7] See the statements of Argentina (ibid., § 614) and Sweden (ibid., § 614); see also the statement of the Netherlands (ibid., § 620).
[8] Chemical Weapons Convention, preamble (ibid., § 599).
[9] United States, Executive Order No. 11850 (ibid., § 627).
[10] See “Russian army not to use defoliants in Chechnya”, ITAR-TASS, Moscow, 17 April 2000 (ibid., § 622).