Cyanazine and simazine—priority 3

Chemical class Triazine herbicides
Chemical Structure


Chemical structure of Cyanazine


Chemical structure of Simazine

CAS Number


Mode of action C—Inhibitors of photosynthesis at photosystem II (PS II inhibitors)
Target pests Algae, broad-leaved weeds and annual grasses
Hosts Horticulture and broadacre crops. Pools, aquariums and ponds
Formulations Liquid, powder, suspension concentrate (flowable concentrate), aqueous concentrate, tablet, liquid concentrate, water dispersible granules and dry flowable
Home garden use Yes
No of Australian Approvals and Registrations

Cyanazine—4 active constituents, 8 products

Simazine—11 active constituents, 90 products
Poison schedule

Cyanazine—Schedule 6.

Simazine—Appendix B, Part 3
Australian Health-based guidance values

Cyanazine: ADI—0.002 mg/kg bw per day (1986)

Simazine: ADI—0.005 mg/kg bw per day (1990)

No Australian ARfD established

Key issues

  • PPE and safety directions may be inadequate to protect workers
  • detected in water in multiple jurisdictions. Not a Public health issue but presents environmental issues
  • withdrawn in US and not approved in the EU

Stakeholder perspective

  • of high importance for pulses and triazine-tolerant canola
  • also critical in control of resistant grass weeds (simazine used more than cyanazine)

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