AGR 3102 Principles of Weed Science Herbicide

1. AGR 3102Principles of Weed ScienceHerbicide Muhammad Saiful Ahmad Hamdani

2. Unit 6 – Topics Covered Herbicide Calculations: a.i. (active ingredients) a.e. (acid equivalent) Calibration

3. Herbicide Calculations • 2 methods: 1) active ingredients (a.i.) 2) acid equivalent (a.e.) 1) a.i. calculation - a.i. is always identified on the herbicide label. - often expressed as either a % or in g/L. - calculations based on dry or liquid formulation.

4. Several calculations to determine the amount of a.i. applied. One of the easiest calculations: g a.i. applied per ha = kg or L of product applied X g active ingredient ha L or kg of product • Example: calculation of dry formulation - Herbicide Plantgard with 30% 2,4-D (note: 30% [w/w] in trade formulation = 30g a.i. in 100g product or 300g a.i. in 1kg product) - Spray recommendation: 2.5kg product / ha - How much is the 2,4-D in the product when we apply 2.5kg of Plantgard per ha???

5. g a.i. applied per ha = kg or L of product applied X g active ingredient ha L or kg of product 2.5kg Plantgard X 300g 2,4-D ha 1kg Plantgard Answer = 750g a.i. 2,4-D per ha applied when spray at recommended rate of 2.5kg Plantgard per ha

6. Example: calculation of liquid formulation - Herbicide Gramoxone with 35% paraquat (note: 35% [w/v] in trade formulation = 35g a.i. in 100mL product or 350g a.i. in 1L product) - Spray recommendation: 3kg a.i. paraquat / ha - How much is the Gramoxone required when we apply 3kg a.i. paraquat per ha??? g a.i. applied per ha = kg or L of product applied X g active ingredient ha L or kg of product 3kg paraquat per ha = ҳL Gramoxone X 350g paraquat ha 1L Gramoxone Answer = 8.57L Gramoxone is required for 1ha when spray with 3kg a.i. paraquat per ha

7. 2) Acid Equivalent (a.e.) calculation • Herbicides a.i. usually in parent acid form (its herbicidally active form), but many are formulated as a derivatives (i.e. esters, salts, amines). • Alterations with herbicide molecules that are acids (at carboxyl [COOH] structure).

9. Why would a herbicide be formulated as a derivative (ester, salt, amine, etc.) of the parent acid? - Increase the ability of the herbicide to penetrate/absorb through the leaf/root much more effectively. - Increase the water solubility of the herbicide • a.e. calculation indicates the amount of an acid herbicide in a formulation. • Some labels indicate both a.i. and a.e. contained in the formulation, while others list only one or the other.

10. Sometimes, the numbers in formulation do not indicate gram active ingredient per L or kg, but rather the acid equivalent per L or kg. • If the g a.e. is specified on the product label, to determine the g a.e applied per ha is substitute g a.e for g a.i. in the equation given previously. • If not specified, calculate a.e. first using this equation: acid equivalent (%) = molecular weight of the acid – 1 X 100 molecular weight of the herbicide - molecular weight of the acid has to minus (-) 1 because one H atom is missing when formed derivative(H+ was replaced by the salt/ester/amine i.e. NH4+ / Na+)

11. Example: • 2,4-D herbicides can be found in ester or amine formulation • 2,4-D dietanolamine salt = 326 mw • 2,4-D acid (pure form) = 221 mw • % of a.e. 2,4,-D = 221-1 X 100 : 67.5% 326 • If in a 2,4-D formulation contains 700g dietanolamine salt per L, the g per L a.e. 2,4-D in the formulation is: 67.5 (a.e.) X 700g/L (2,4-D salt formulation) = *472.5g/L 100 • 472.5g is the actual a.i. 2,4-D (in a.e.) that cause phytotoxicity to plants/weeds

12. Now, how much g a.e. 2,4-D per ha is applied if the spray dosage recommendation is 5L product per ha? g a.e. applied per ha = kg or L of product applied X g acid equivalent ha L or kg of product g a.i. applied per ha = 5L X 472.5g ha L = 2362.5g a.e. 2,4-D per ha is applied when sprayed at the recommended rate of 5L/ha product

13. Calibration • A technique to help you calculate how much water / chemical mix your sprayer puts out to ensure that the correct rate of chemical is applied to the target plant. • 2 types of sprayer: knapsack sprayer and boom-sprayer. • Calibration will be emphasized on knapsack sprayer.

15. Knapsack Sprayer Calibration 1) Measure the spray width of the nozzle(s) on a dry surface (in m). 2) Spray a test area at the intended pressure and walking pace. Record distance (in m) covered in one minute (min). 3) Measure the nozzle output in L over one min in a measuring jug (L/min). Repeat all steps at least twice. 4) The spray volume can be calculated by the following formula: Application rate (L/ha) = nozzle output (L/min) x 10,000 m2 spray width (m) x walking speed (m/min)

16. For example: • Average nozzle output in 1 minute: = 3 L • Spray width: = 1 m • Average walking speed: = 100 m/min • Application rate (L/ha) = 3 x 10,000 1 x 100 = 30,000 100 • = 300 L/ha application rate (water)

17. How much to put in a tank??? • The following formula can be used to determine the amount of product needed for each tank: Product/tank (L or kg) = recommended rate (L/ha or kg/ha) x tank size (L) application rate (L/ha) • For example: Recommended product dosage: 5 L/ha Application rate: 300 L/ha Spray tank size: 20 L Calculation: Product/tank (L/ha) = 5 x 20 300 Answer = 0.33 L or 330 ml • 330 ml of the product is added to a 20 L knapsack sprayer to give the recommended spray rate of 5 L/ha.

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