1/18/2023

Corn Leaf Removal Impact on Yield and Stalk Quality

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Agronomy Research Update
Written by Nate LeVan, Troy Deutmeyer, and Dan Berning, Pioneer Agronomy Sciences

Key Findings

The impact of leaf removal on yield and late season stalk integrity is highly dependent on which leaves on the plant are removed.

Yield components of kernel number and ear weight were both affected by loss of leaf area at the R4 and R5 stage of crop development.

This study demonstrated the importance of protecting the crop from leaf area loss as late as the R5 stage of crop development.

Objectives

Loss of healthy leaf area in corn due to factors such as foliar diseases, pest infestations, or hail damage reduces the supply of photosynthate for filling the ear, which can reduce yield.
Lost leaf area can also lead to reduced stalk quality and standability as the plant remobilizes carbohydrates from the stalk to compensate for the reduction in photosynthesis.
Field demonstrations were conducted in Iowa in 2022 in which leaves were removed from corn plants during grain fill to show the effects of reduced leaf area on yield and stalk quality.
In one demonstration, leaves were removed at the R2-R3 development stage and in the other at the R4 stage and R5 stage.

All leaves below ear removed at R3 stage of crop development.

Figure 1. All leaves below ear removed at R3 stage of crop development.

All leaves above corn ear removed at R3 stage of crop development.

Figure 2. All leaves above ear removed at R3 stage of crop development.

Leaf Removal at R2 - R3

Leaves were removed at R2- R3 stage of crop development at 3 locations across north-central Iowa in 2 different hybrids at each location to reduce photosynthetic area. Four separate leaf removal treatments were compared:
1. All leaves below the ear (Figure 1)
2. Ear leaf only
3. All leaves above the ear (Figure 2)
4. No leaves removed (check)
Each treatment block consisted of 4 rows by 17.5 feet.
Harvest yield was determined by weighing the ears in each treatment, measuring the grain moisture, and correcting the yield to 15.5% grain moisture

Leaf Removal at R2 - R3 - Results

Removing ear leaf only:
- No change in grain moisture (Figure 3).
- 1% reduction in ear weight and grain yield (Figure 4).
- No effect on stalk quality.
Removing the leaves below the ear:
- No change in grain moisture.
- 4% reduction in ear weight and grain yield.
- No effect on stalk quality.
Removing the leaves above the ear:
- 0.53% dryer than the check.
- 22% reduction in ear weight and grain yield.
- Significant amount of stalk cannibalization.

Grain moisture - bu per acre - of defoliation treatments averaged across 3 north-central Iowa locations.

Figure 3. Grain moisture (bu/acre) of defoliation treatments averaged across 3 north-central Iowa locations.

Grain yield - bu per acre - of defoliation treatments averaged across 3 north-central Iowa locations.

Figure 4. Grain yield (bu/acre) of defoliation treatments averaged across 3 north-central Iowa locations.

Plant health comparison at harvest.

Figure 5. Plant health comparison at harvest.

Leaf Removal at R4 and R5

Leaves were removed at R4 and R5 stage of crop development at 1 location in northeast Iowa on one hybrid to induce loss of photosynthetic area. Four separate treatments were compared:
1. All leaves below the ear
2. Ear leaf only
3. All leaves above the ear
4. No leaves removed (check)
The field was sprayed at brown silk with fungicide and again 21 days later to prevent foliar disease development.
Harvest yield was determined by weighing 20 ears in each treatment, measuring the grain moisture, and correcting the yield to 15.5% grain moisture.
Five random ears from each treatment were used to determine average kernel row number and length of each treatment.

Leaf Removal at R4 and R5 - Results

Removing leaves above and below the ear leaf at the R4 stage of development tended to have a greater impact on yield loss than defoliation at R5.
Removing the ear leaf only:
- 1.5% reduction in ear weight at R4 removal (Figure 4).
- 3.0% reduction in ear weight at R5 removal.
- No effect on stalk quality (Figure 5).
Removing the leaves below the ear:
- 12.0% reduction in ear weight at R4 removal.
- 6.8% reduction in ear weight at R5 removal.
- Little to no effect on stalk quality.
Removing the leaves above the ear:
- 27.7% reduction in ear weight at R4 removal.
- 19.8% reduction in ear weight at R5 removal.
- Significant amount of stalk cannibalization with both timings (Figure 6).

Percent yield loss with defoliation at R4 and R5 at the northeast Iowa demonstration location.

Figure 6. Percent yield loss with defoliation at R4 and R5 at the northeast Iowa demonstration location.

Stalk integrity comparison at harvest.

Figure 7. Stalk integrity comparison at harvest.

Ear weight with defoliation at R4 and R5 at the northeast Iowa demonstration location.

Figure 8. Ear weight with defoliation at R4 and R5 at the northeast Iowa demonstration location.

Average kernel count per ear with defoliation at R4 and R5 at the northeast Iowa demonstration location.

Figure 9. Average kernel count per ear with defoliation at R4 and R5 at the northeast Iowa demonstration location.

Conclusions

Both demonstrations illustrate the ENTIRE canopy is important to final yield, even as late as the R5 stage of crop development.
Growers should proactively protect healthy leaf area with fungicide applications when there is a risk a foliar disease infestation reaching an economic level.
- Some diseases, such as tar spot, have a two-week incubation period and can develop very rapidly. It is important to recognize and consider this in a scouting and treatment plan.
- If enough leaf area is lost prior to grain physiological maturity, it can lead to solubilization and remobilization of the carbohydrates in the stalk. This can result in poor late season stalk integrity, stalk lodging and harvest issues.

Key Findings