Application Methods of Herbicides

Herbicides can be applied to soil or foliage depending on weed type, crop stage, and chemical properties of the herbicide.

1 Soil Application

Herbicide is applied to the soil before or after planting, targeting germinating weed seeds or young seedlings.

a) Soil Surface Application

• Applied uniformly on the soil surface without incorporation.
• Forms a toxic layer that kills germinating weed seedlings.
• Effective mainly on shallow germinating weeds.
• Herbicides used: Triazines (Atrazine, Simazine), Ureas (Diuron), Anilides (Alachlor).
• Example: Atrazine in maize and sorghum.

b) Soil Incorporation

• Herbicide is sprayed on soil surface and then mixed into soil using tillage or irrigation.
• Prevents loss due to volatilization (evaporation) or photodecomposition (breakdown by sunlight).
• Suitable for volatile herbicides.
• Herbicides used: Trifluralin, EPTC (carbamates).
• Example: Trifluralin incorporated before sowing groundnut or soybean.

c) Sub-Surface Application

• Herbicide is injected below the soil surface (root zone).
• Targets deep-rooted perennial weeds.
• Done with specialized injectors.
• Herbicides used: Dalapon, MSMA.
• Example: Cyperus rotundus (nutgrass) and Cynodon dactylon (bermudagrass).

d) Band Application

• Herbicide applied in narrow strips/bands along crop rows.
• Weeds between rows are controlled by mechanical weeding or intercultivation.
• Economical as it reduces chemical use.
• Herbicides used: Atrazine, Alachlor.
• Example: Atrazine applied in bands on maize rows at sowing.

2️. Foliar Application

Herbicide is sprayed directly on the leaves and stems of weeds. It can be selective or non-selective.

a) Blanket Application

• Sprayed uniformly over entire crop field (crops + weeds).
• Only selective herbicides are safe for crops.
• Herbicides used: 2,4-D, MCPA, Atrazine.
• Example: 2,4-D in wheat to control broadleaf weeds.

b) Directed Application

• Spray aimed only at weeds, avoiding crop foliage.
• Used with non-selective herbicides to avoid crop damage.
• Herbicides used: Paraquat, Glyphosate.
• Example: Paraquat in cotton rows, applied between crop rows without touching cotton leaves.

c) Spot Applicatio

• Herbicide applied only to localized patches of weeds.
• Saves time and cost.
• Useful in orchards, plantations, or when weeds occur irregularly.
• Herbicides used: Glyphosate, Glufosinate.
• Example: Spot-spraying nutgrass patches in sugarcane fields.

Special Methods of Herbicide Application

Pre-Emergence Application

• Applied after sowing but before crop and weed emergence.
• Forms a toxic layer in the soil.
• Example: Pendimethalin in soybean and pulses.

Post-Emergence Application

• Applied after crop and weed emergence.
• Selective herbicides must be used to avoid crop injury.
• Example: 2,4-D in wheat, Bispyribac-sodium in rice.

Lay-by Application

• Applied after the last cultivation, when crops are established.
• Controls late flushes of weeds.
• Example: Diuron in cotton.

Herbigation

• Application of herbicides through irrigation water.
• Ensures uniform distribution.
• Example: EPTC applied through irrigation in maize.

Benefits of Herbicide Application

• Saves labor and time compared to manual weeding.
• Effective against weeds in crop rows where mechanical methods are difficult.
• Useful in zero/minimum tillage systems.
• Provides early-season weed control.
• Controls perennial weeds better than other methods.