In Ontario, the following 25 weeds are designated as noxious under the Weed Control Act:
| Common Name | Scientific Name |
|---|---|
| Barberry, common | Berberis vulgaris L. |
| Bedstraw, smooth | Galium mollugo L. |
| Buckthorn, European | Rhamnus cathartica L. |
| Chervil, wild | Anthriscus sylvestris (L.) Hoffmann |
| Coltsfoot | Tussilago farfara L. |
| Crupina, common | Crupina vulgaris Cass. |
| Cupgrass, woolly | Eriochloa villosa (Thunb.) Kunth |
| Dodder spp. | Cuscuta spp. |
| Dog-strangling vine | Vincetoxicum rossicum (Kleopow) Barbar. |
| Dog-strangling vine, black | Vincetoxicum nigrum (L.) Moench |
| Goatgrass, jointed | Aegilops cylindrica |
| Hogweed, giant | Heracleum mantegazzianum Sommier & Levier |
| Knapweed spp. | Centaurea spp. |
| Kudzu | Pueraria montana (Lour.) Merr. |
| Parsnip, wild | Pastinaca sativa L. |
| Poison-hemlock | Conium maculatum L. |
| Poison-ivy | Toxicodendron radicans (L.) Kuntze |
| Ragweed spp. | Ambrosia spp. |
| Ragwort, tansy | Senecio jacobaea L. |
| Sow-thistle spp. | Sonchus spp. |
| Spurge, cypress | Euphorbia cyparissias L. |
| Spurge, leafy | Euphorbia esula L. |
| Thistle, bull | Cirsium vulgare (Savi) Tenore |
| Thistle, Canada | Cirsium arvense (L.) Scopoli |
| Tussock, serrated | Nassella trichotoma Hackel ex Arech. |
Halton region Master Gardeners 