Kristen Callow, Weed Management Program Lead – Horticulture, OMAFRA
Why is water volume so important when you apply herbicides? Inadequate spray volumes will result in poor coverage of the herbicide on the weed surface. Herbicide coverage is critical because the spray solution acts as the carrier of the herbicide active ingredients that are absorbed by the weeds causing death. Weed density, environmental conditions, and growth stage of the weeds should be determined prior to making applications.
Higher water volumes are usually required for contact herbicides (Group 6, 10, 14, 22 and 27), particularly when:
– spraying a pre-seed burn off when weeds are small
– spraying through a dense canopy
– spraying later in the day or evening when weed leaves may not be as horizontal to intercept the herbicide
Follow label directions to maximize herbicide performance.
Table 1. Water Volumes for the Best Herbicide Results
| Herbicide Group | Site of Action | Herbicide Example | Water Volume** for Best Results (L/ha) | Water Volume** for Best Results (Imp. gallon/ac) | |
| 1 | Inhibitors of acetyl CoA carboxylase (ACCase): | Assure II, Excel, Poast Ultra, Select, Venture | 100 – 300 | 10.7 – 32.1 | |
| 2 | Inhibitors of acetolactate synthase (ALS) and also called acetohydroxyacid synthase (AHAS) | Prism, Pursuit | 100 – 400 | 10.7 – 42.8 | |
| 3 | Microtubule assembly inhibitors | Prowl H2O | 200 minimum | 21.4 | |
| Treflan | 100 minimum | 10.7 | |||
| 4 | Synthetic auxins | 2,4-D, Dicamba, MCPA | 100 – 650 | 10.7 – 69.5 | |
| 5 | Inhibitors of photosynthesis at photosystem II, Site A | Princep Nine-T | 300 | 32.1 | |
| Sencor, Sinbar | 150 – 300 | 16 – 32.1 | |||
| 6 | Inhibitors of photosynthesis at photosystem II, Site B | Basagran | 100 – 400 | 10.7 – 42.8 | |
| 7 | Inhibitors of photosynthesis at photosystem II, Site B (alternate binding site) | Lorox | 100 – 600 | 10.7 – 74.9 | |
| 9 | Inhibitors of 5-enolpyruvylshikimimate-3-phosphate synthase (EPSP) | Round-up (glyphosate) | 50 – 300 | 5.3 – 32.1 | |
| 10 | Inhibitors of carotenoid biosynthesis | Ignite | 170 – 220 | 18.2 – 23.5 | |
| 13 | Diterpene synthesis inhibitor | Command | 95 – 375 | 10.2 – 40.1 | |
| 14 | Inhibitors of protoporphyrinogen oxidase (Protox) | Aim, Chateau, Goal 2XL | 100 – 500 | 10.7 – 53.5 | |
| 15 | Conjugation of acetyl co-enzyme A | Dual II Magnum | 150 – 400 | 16 – 42.8 | |
| 20 | Inhibits cell wall synthesis Site A | Casoron | Non specified | Non specified | |
| 22 | Photo system I – electron diverters | Gramoxone | 187 -1100 | 20 – 117.6 | |
| 29 | Inhibitors of cellulose biosynthesis | Alion | Minimum 93 | Minimum 9.95 | |
*Conversion factor: Multiply gal/ac by 9.35 to get L/ha
**Volumes on herbicide labels vary based on crop type, crop growth stage, weed type and weed growth stage
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