Leaf Senescence in Corn: How Many Yellow Leaves Are Normal?

A modern 110-day corn hybrid in central Iowa produces about 19 leaves but can only maintain 12-14 leaves on the plant. The first leaves begin senescing around the V5 stage, and by silking (R1) approximately 6-8 bottom leaves have already senesced (Figure 1). From R1 to R5, leaf senescence progresses slowly, with about 2-3 additional leaves senescing. Most leaves are rapidly senescing near physiological maturity (R6) or black layer. This pattern is normal and reflects how corn maintains a productive canopy during grain filling while recycling nutrients from older leaves to developing kernels.

Figure 1: Leaf number production and senescence of a 110-day corn growing in central Iowa. Data are averages over two years and several hybrids. 

Many farmers become concerned when they see senesced leaves near the bottom of the plant at silking. However, the position of the senesced leaves is more important than their number. The lower canopy receives very little sunlight, and these leaves are generally small, so they contribute little to green canopy cover, light interception and photosynthesis (Figure 2). In contrast, the ear leaf and two leaves above and below the ear are the largest, intercept most of the incoming sunlight, and provide most of the carbohydrates needed for grain filling.

Figure 2: Green and senesced leaf area index of a 110-day corn growing in central Iowa. Data are averages over two years and several hybrids. 

People often assume that leaf senescence equals nitrogen deficiency. However, this is not always the case as leaf senescence is a natural process, though several factors can accelerate it such as shading, water stress, foliar diseases, and hybrid genetics, along with nitrogen deficiency. Modern hybrids generally maintain green leaf area longer than older hybrids. 

When should you worry?

Normal senescence progresses from the bottom upward. Concern is warranted when the middle canopy leaves begin senescing before the dent stage (R5), or when foliar diseases cause premature leaf death, as occurred in many Iowa fields last year. Early loss of green leaf area shortens the grain-filling period, reduces photosynthesis, and ultimately lowers kernel weight and grain yield.

Bottom line is that seeing senesced leaves near the bottom of the plant at silking is completely normal. Those leaves have already done their job. The leaves that matter most are the middle canopy leaves. 

For additional information on maize leaf development, canopy senescence, and recent advances in maize breeding, see the references below

Darra, N., Danalatos, G.J.N., Ferela, A., Saenz, E., Trifunovic, S., Kosola, K.R., Tao, N., Vartorelli, F., Schnable, P.S., Vyn, T.J., & Archontoulis, S.V. 2026. Light interception and radiation use efficiency in maize – Quantifying breeding and plant density effects since 1980. Field Crops Research, 347, 110651. https://doi.org/10.1016/j.fcr.2026.110651

dos Santos, C.L., Miguez, F.E., King, K.A., Ruiz, A., Sciarresi, C., Baum, M.E., Danalatos, G.J.N., Stallman, M., Wiley, E., Pico, L.O., Thies, A., Puntel, L.A., Topp, C.N., Trifunovic, S., Eudy, D., Mensah, C., Edwards, J.W., Schnable, P.S., Lamkey, K.R., Vyn, T.J., & Archontoulis, S.V. 2023. Accelerated leaf appearance and flowering in maize after four decades of commercial breeding. Crop Science, 63, 2750–2762. https://doi.org/10.1002/csc2.21044.

dos Santos, C.L., Abendroth, L.J., Coulter, J.A., Nafziger, E.D., Suyker, A.E., Yu, J., Schnable, P.S., & Archontoulis, S.V. 2022. Maize leaf appearance rates: A synthesis from the United States Corn Belt. Frontiers in Plant Science, 13, 872738. https://doi.org/10.3389/fpls.2022.872738 

Kalogeropoulos, G., Elli, E.F., Trifunovic, S., & Archontoulis, S.V. 2024. Historical increases of maize leaf area index in the U.S. Corn Belt due primarily to plant density increases. Field Crops Research, 318, 109615. https://doi.org/10.1016/j.fcr.2024.109615.

Kalogeropoulos, G., Saenz, E., Danalatos, G.J.N., Baum, M.E., Ferela, A., Trifunovic, S., & Archontoulis, S.V. 2026. Four decades of crop improvement decreased specific leaf nitrogen and reshaped canopy trait profiles in maize. Field Crops Research, 340, 110387.