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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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