Are You Applying the Proper Water Volume with your Herbicides?

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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