Preparation for harvesting maize: Practical guide for farmers

Maize is one of the most important staple and commercial crops in Eswatini. However, Soil Science and Plant Nutrition Research Officer Bongani Mvubu says a successful maize enterprise does not end in the field, it depends greatly on proper harvesting and post-harvest handling. “Poor timing, inadequate drying and weak storage facilities can lead to serious losses through pests, mould and spoilage,” he shared.

1. Preparation for harvesting maize

Preparation should begin 2–3 weeks before expected harvest. The following steps are critical:

1. a) Field assessment

• Monitor crop maturity and moisture levels.
• Check for lodging (fallen plants).
• Inspect for pest damage (stalk borers, rodents, birds).

1. b) Organise labour and equipment

• Arrange sufficient labour.
• Prepare harvesting tools (hand slashers, sickles, combine harvesters, maize shellers if needed).
• Clean and disinfect storage facilities.

1. c) Prepare storage in advance

• Storage must be ready before harvesting begins. This includes:
• Constructing or repairing maize cribs.
• Ensuring fencing is intact.
• Clearing vegetation around storage areas.

Failure to prepare storage early often results in maize being heaped on the ground, increasing contamination and moisture absorption.

2. Maize crib construction

A maize crib is a well-ventilated storage structure used to dry and store maize cobs before shelling.

Standard elevated maize crib (recommended design)

For small to medium-scale farmers:

• Width: 2 metres
• Length: 4 metres, can be more depending on produce
• Height above ground: 1 metre
• Wall height: 2–3 metres
• Roof overhang: At least 0.5 metres to prevent rain splash
• Steps: To enable loading maize on the crib, but removed once crib is full

These dimensions allow good air circulation while providing sufficient storage capacity.

Key construction features

1. Elevation (1 metre above ground)

• Supported by strong treated wooden poles.
• Prevents moisture absorption from soil.
• Reduces rodent access.

2. Rat Baffles (Rat Guards)

• Installed on each supporting pole.
• Made from smooth metal sheets shaped like inverted cones.
• Prevent rats from climbing into the crib.

3. Corrugated iron roof

• Galvanized iron sheets.
• Sloped for rainwater runoff.
• Wide overhang protects walls from direct rain.

4. Fencing

• Wire mesh fence around the crib.
• Prevents livestock and unauthorized access.
• Recommended fence height: 1.5 metres.
• All wood should be treated against termites and decay.

3. Why use a maize crib?

Using a maize crib offers several advantages:

• Proper drying

The open slatted design allows continuous airflow, reducing moisture content naturally.

• Reduced post-harvest losses
• Minimises mould growth.
• Reduces aflatoxin contamination risk.
• Prevents rodent and livestock damage.

• Improved grain quality

Well-dried maize has:

• Better market value
• Longer storage life
• Higher seed viability

4. Food safety

Poor drying leads to fungal growth, which may produce toxins harmful to humans and livestock.

5. When to harvest maize

Harvest timing is critical.

Signs of Physiological Maturity

• Husks turn brown and dry.
• Cobs droop downward.
• Kernels are hard and shiny.
• Black layer forms at the base of kernels.

Moisture content

• Ideal harvesting moisture: 20–25% (on cob)
• For storage: Must be dried to 12–13% (shelled grain)

Harvesting too early results in:

• Shrivelled grain
• Poor weight
• Higher drying costs

Harvesting too late increases:

• Field pest damage
• Lodging
• Theft risk

6. How to harvest maize

Step 1: Select mature cobs

Only harvest fully mature and dry cobs.

Step 2: Hand harvesting

• Twist or snap cobs from stalks.
• Avoid pulling entire plants unnecessarily.

Step 3: Remove damaged cobs

• Separate mouldy or insect-damaged cobs.
• Do not mix with good maize.

Step 4: Transport carefully

• Use clean bags or trailers.
• Avoid placing cobs directly on wet soil.

Step 5: Load into crib

• Arrange evenly for airflow.
• Do not compress tightly.

Allow maize to dry in crib for 4–8 weeks before shelling (depending on weather conditions).

7. What to avoid when harvesting maize

 Harvesting wet maize: Leads to mould and aflatoxin contamination.

 Heaping maize on bare ground: Causes contamination and moisture absorption.

 Mixing good and bad cobs: Accelerates spoilage.

Poor ventilation: Closed storage encourages fungal growth.

Delayed harvest: Increases pest and rodent damage.

Using untreated wood: May lead to termite damage and structural collapse.

8. Additional post-harvest recommendations

• Shell maize only after proper drying.
• Use moisture meters where available.
• Treat shelled maize with recommended grain protectants.
• Store in clean, dry, airtight bags or silos.
• Regularly inspect for pests.