Protecting the upper canopy in a corn crop is an essential step toward maximizing yield potential.
Removing the upper canopy leaves reduced yields by 21% and 31% at the R3 and R1 timings, respectively.
Upper canopy leaf removal at R1 timing increased lodging by roughly 4 times (38-41% lodging).
Corn plant leaves harvest sunlight for energy to use with water, nutrients and carbon dioxide to ultimately produce plant dry matter.1 Early in the growing season the process is slow, but as plant size increases, the rate of dry matter accumulation increases. The interaction between plant leaves and grain is ultimately how yield within the plant is produced and is often referred to as a source-sink relationship.2 Energy is “sourced” through photosynthesis in leaves and eventually “sinks” into developing grain kernels.
Environmental stresses that minimize leaf development will reduce photosynthetic efficiency. This reduces the overall source of energy and has an impact on the sink, or grain development. Leaf damage from hail or disease can quickly minimize the leaf source and result in sugars being moved from lower stalks or roots in efforts to meet the sink demand for developing kernels. Sourcing sugars from stalks rather than leaves can often result in weakening of the stalks and potential lodging. Protecting the upper corn canopy is an important management consideration when deciding on fungicide application and timing.
Leaf Defoliation Trials
Trials were established at Clinton, IL, Slater, IA, and Seward, NE, to determine the effect of leaf removal on grain yield and stalk quality at 2 different timings. 2 hybrids with similar maturities were selected to determine if hybrids differed in response to leaf removal.
Replicated treatments included an untreated check (no leaf removal), ear leaf plus 1 leaf above and below removed, all leaves below the ear leaf removed, and all leaves above the ear leaf removed. Leaf removal treatments were performed at the growth stage timings of R1 (silk emergence) and R3 (milk stage), which occurs about 20 days after silking. To assess stalk strength, a push test was conducted on 10 plants per plot, recording the number of plants that were weak enough to break at harvest time.
Figure 1. Treatment photos: Upper canopy removed (A), ear leaf plus 1 leaf above/below removed (B), lower canopy removed (C) and normal canopy (D).
Yield and Lodging Response
Yield reductions were observed at all leaf removal timings and positions. In general, all sites responded similarly and were averaged together in results shown (Graph 1). Removal of lower and mid canopy leaves at the R3 timing resulted in similar yield loss ranging from 6-8% for both hybrids. Earlier removal of the mid and lower leaves at the R1 stage similarly showed 6-7% yield loss with Golden Harvest® corn hybrid G10L16, although Golden Harvest corn hybrid G10D21 lost 11-13% yield potential at the same timings. The most severe yield loss occurred through removal of the upper canopy with G10L16 and G10D21 both losing 20-22% at R3 timing and 31% at R1 timings. Removal of lower canopy or mid canopy reduced yields similarly, although not to the magnitude of removing upper canopy leaves, highlighting the importance of protecting the upper canopy. G10D21 was more sensitive to lower and mid canopy leaf removal at R1 timing as compared to G10L16.
Graph 1. Hybrid yield response to leaf removal position and timing
Leaf removal impact on stalk strength was also monitored as reductions in photosynthesis often reduce late-season standability. Leaf removal of mid and lower canopy at R3 timing had little influence on standability for either hybrid, although lodging doubled when upper canopy leaves were removed (Graph 2). Removing leaves earlier in the grain fill process (R1) had a greater effect on standability with all 3 removal positions. Hybrids also responded differently to the area where leaves were removed. Standability of G10L16 worsened to 30-38% lodging across all 3 timings. Lower leaf removal at R1 did not affect G10D21 standability, although it worsened when mid (23% lodging) and upper (41% lodging) leaves were removed.
Graph 2. Artificial stalk lodging resulting from leaf removal position and timing These trials illustrate how hybrids can respond differently to stress, such as leaf removal. Overall, the yield potential of G10L16 was less influenced by leaf removal. However, to maintain yield, it likely reallocated sugars more aggressively from lower stalks, resulting in greater potential to lodge. G10D21 was more sensitive to R1 leaf removal, as shown with yield loss results. However, other than the most severe scenario of R1 removal of upper canopy, G10D21 standability results were less impacted.
Factors that Reduce Source Strength
Weather events that reduce leaf area can reduce source capacity significantly, especially when occurrences happen early in the reproductive stages. Leaf photosynthesis can be reduced several ways:
- Reduced leaf number and size
- Early drought
- Nutrient deficiencies
- Loss of physical leaf area
- Hail
- Root lodging
- Insect damage
- Disease lesions on leaves
- Reduced photosynthesis efficiency
- Excessive cloud cover for multiple days
Irrigation, good nutrient management and protection of upper canopy leaves with fungicide can improve plant photosynthetic efficiency and help improve sugar supply to develop heavier kernels that improve yield potential and test weights.
To learn more about the Golden Harvest Agronomy in Action corn photosynthesis response trial, watch this video.
References
1Ritchie, S., J. Hanway, and G. Benson. 1997. How a corn plant develops. Iowa State Cooperative Extension Service Special Report No. 48.
2Smith, M, I. Rao, and A. Merchant. 2018. Source-sink relationships in crop plants and their influence on yield development and nutritional quality. Frontiers of Plant Science. December 20, 2018.
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