Pre-Emergence Herbicide Guide for Maize

Pre-emergence herbicides are applied to the soil after planting but before crop or weed emergence. They are a cornerstone of maize weed management in Southern Africa, providing season-long or early-season control of grasses and broadleaf weeds.

Why Use Pre-Emergence Herbicides?

Maize is most vulnerable to weed competition during the first 4–6 weeks after planting (the critical weed-free period). Pre-emergence herbicides establish weed control from day one, before manual labour or cultivation can practically intervene.

Key Active Ingredients

Tank Mix Combinations

Pre-emergence herbicide programs typically combine a grass herbicide + a broadleaf herbicide:

• •Metolachlor + Atrazine: Most widely used combination in maize; covers grasses + broadleaves
• •Pendimethalin + Atrazine: Good alternative, especially where metolachlor resistance is a concern
• •S-metolachlor + Flumioxazin: Excellent broadleaf activity without atrazine

Application Technique

1. •Apply within 3 days of planting
2. •Use 200–300 L/ha water volume with flat fan nozzles
3. •Avoid overlap and misses — uneven application leads to weed escapes
4. •All pre-emergence herbicides require rainfall (10–20 mm) within 5–7 days of application to activate
5. •Do not incorporate mechanically except in very dry conditions

Soil Factors

• •Clay soils: Use higher label rates; increased adsorption
• •Sandy soils: Use lower rates; increased leaching risk with soluble products
• •High organic matter: Higher rates needed; product binds to organic matter
• •pH: Most pre-emergence herbicides work best at pH 5.5–7.0

Safety and Carryover

Atrazine has a long soil half-life (60–150 days). Observe plant-back restrictions for sensitive crops (sunflower, beans, sorghum) following maize with atrazine. Check the label for specific restrictions.