Corn Harvest Timing

Optimal Corn Harvest Moisture

The optimal harvest moisture for corn is 22-25%, balancing drying costs with field loss risk:

22-25% moisture: Ideal harvest window. Minimal field loss, reasonable drying costs, good grain quality. Most farmers target this range.

25-28% moisture: Early harvest. Higher drying costs ($0.20-0.30/bu extra), but minimal field loss. Good if weather is deteriorating.

20-22% moisture: Mid harvest. Lower drying costs, slight field loss risk. Common for non-irrigated corn.

18-20% moisture: Late harvest. Lowest drying costs, but increasing field loss risk from lodging and ear drop.

Below 18% moisture: Field dry-down. No drying cost, but significant lodging and weather loss risk. Generally not recommended.

Why Harvest at 22-25% Moisture?

The 22-25% moisture range is optimal for several reasons:

1. Drying cost balance: At 22-25% moisture, drying costs are $0.10-0.20/bu, manageable for most operations. Drying 28% moisture corn costs $0.25-0.35/bu — significantly reducing profit.

2. Field loss risk: Below 20% moisture, lodging and ear drop increase rapidly. Each week past maturity, expect 0.5-2 bu/ac field loss from lodging and ear drop.

3. Grain quality: Corn harvested at 22-25% moisture and dried gently has higher test weight and less stress cracking than corn harvested wetter or drier.

4. Weather risk: Late harvest increases risk of storms, snow, and freezing conditions that can delay harvest and cause significant losses.

5. Logistics: Starting harvest at 25% moisture allows you to spread the harvest window and avoid bottlenecks at harvest peak.

Corn Field Dry-Down Rate

After physiological maturity (R6, black layer), corn loses moisture in the field at a predictable rate:

September (warm/dry): 0.5-1.0 moisture point per day

October (cool/wet): 0.25-0.5 moisture point per day

November (cold): 0.1-0.25 moisture point per day (essentially stops)

Factors affecting dry-down rate:

• Hybrid: Some hybrids dry down faster than others
• Husk: Tight husks slow dry-down; loose husks speed it
• Eear angle: Upright ears dry slower than drooping ears
• Weather: Warm, dry, windy weather speeds dry-down
• Plant population: Higher populations dry slightly faster

Field Loss Management

Every day corn stays in the field past maturity, you risk yield loss from lodging, ear drop, and weather:

Lodging: Stalks break or lean, making harvest difficult. Causes: stalk rot, insect damage, high wind. Each lodging event can lose 5-15 bu/ac.

Ear drop: Ears fall off the stalk before harvest. Causes: weak shanks, insect damage, high wind. Each ear drop event can lose 2-5 bu/ac.

Weather losses: Storms, snow, freezing rain can knock down corn and make harvest impossible. Major storms can cause total crop loss.

Wildlife damage: Deer, raccoons, and birds can cause significant losses in some areas, especially late in the season.

Strategy: Harvest higher-risk fields first (poor stalks, flat ground, exposed locations). Save lower-risk fields for later harvest.

Stalk Quality Assessment

Before deciding harvest order, assess stalk quality to identify fields at highest lodging risk:

Push test: Push corn stalks about 10 inches from vertical at chest height. If the stalk breaks or doesn't spring back, it's at risk of lodging.

Pinch test: Pinch the lower stalk internodes. If they crush easily, stalk rot is present and lodging risk is high.

Root test: Dig up plants and check root health. Poor roots = lodging risk, especially in high winds.

Harvest fields with poor stalk quality first, even if moisture is higher. Drying cost is cheaper than field loss from lodging.

Harvest Equipment Considerations

Combine settings affect harvest loss, grain quality, and throughput:

• Header height: Set just below ear height. Too low wastes grain; too high leaves ears.
• Stalk roll speed: Match to ground speed. Too fast = grain damage; too slow = unthreshed ears.
• Cylinder/rotor speed: Match to moisture. Higher moisture = higher speed; lower moisture = lower speed.
• Sieve settings: Adjust for grain size and moisture. Check behind combine for clean grain.
• Ground speed: 2.5-3.5 mph typical for corn. Faster increases header loss.

Check harvest loss daily. Standard acceptable loss is 1-2 bu/ac. Above 3 bu/ac, adjust combine settings.

Storage Considerations

Plan storage before harvest begins:

• Bin capacity: Calculate how much bin space you'll need. 1 bu = 1.25 cu ft.
• Drying capacity: Match dryer capacity to combine capacity. Bottleneck = lost combine time.
• Aeration: Cool grain quickly to 40°F by November, 30°F by December.
• Moisture for storage: 15% for short-term (under 6 months), 13-14% for long-term.
• Marketing plan: Know which bushels you'll sell at harvest vs. store. Don't pay storage on bushels you'll sell.