AGR 3102AGR 3102Principles of Weed SciencePrinciples of Weed Science

HerbicideHerbicide

Muhammad Saiful Ahmad HamdaniMuhammad Saiful Ahmad Hamdani

Unit 6 – Topics CoveredUnit 6 – Topics Covered

Herbicide Calculations:

a.i. (active ingredients)

a.e. (acid equivalent)

Calibration

• 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.

Herbicide CalculationsHerbicide Calculations

• 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???

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

• 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

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).

• 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.

• 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+)

• 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

• 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

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.

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)

• 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)

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/haApplication rate: 300 L/haSpray tank size: 20 LCalculation:

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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