C.O.R.N. Newsletter: 2020-22

As temperatures remain hot for much of the state, corn continues to put on leaf collars and is approaching the start of flowering. Corn is a plant that has separate male (anthers on the tassel) and female (silks in the ear) flowers, and it is critical that the timing of flower emergence and activity overlap (sometimes referred to as the ‘nicking’ period) to ensure good pollination and kernel set. Another term used for flowering synchrony is the ‘anthesis-silking interval,’ which is the time from pollen shedding to silk emergence.

The start of pollen shed from the anthers on the tassel is called ‘anthesis’ and can occur before the plant reaches the VT growth stage. The VT growth stage is defined as “plants with all branches of the tassel fully visible, extended outward, and not held in by the upper leaves.” Many modern hybrids begin shedding pollen while the tassel is still emerging from the surrounding leaves.  

Silk emergence signals the start of the R1 growth stage, which is defined as “one or more silks extending outside the husk leaves of the ear.” In many modern hybrids, we will actually see silks emerging prior to the tassel being fully emerged. This leads to a negative anthesis silking interval (silk emerges before pollen shedding), which is one way breeders have improved yields in modern hybrids. Shortening the time from anthesis to silking increases the likelihood of pollination and has helped increase yield over time. High temperatures and low moisture levels may lengthen the anthesis-silking interval compared to normal conditions, but both anthesis and silking last for approximately six days and occur throughout the day, so poor nick is not usually a common occurrence. Planting multiple hybrids in a field that vary slightly in their relative maturity or days to flowering can also help reduce the likelihood that the nicking period is missed.

Both high temperatures and moisture can also affect pollination success. It is recognized that temperatures above 90 degrees F can cause pollen to be non-viable, but much of the pollen shed in corn occurs in the morning hours before temperatures climb to these levels. Additionally, new pollen is made each day during this phase. The longevity of the pollen shed at lower temperatures can also be affected by the relative humidity. Pollen sheds from the plant with a moisture content of 50-65%, and can lose viability once the moisture content drops to 30%. In low relative humidity and high temperature conditions, this can happen more quickly. Moisture stress can slow the rate of silk elongation as this is driven by turgor pressure. Low relative humidity in combination with high temperatures can cause silks to desiccate and can reduce pollination success, but this may not be a major issue given the silks are close to the stalk and in the middle of the canopy where relative humidity tends to be greater than outside the canopy.

Sources

Abendroth, L.J., Elmore, R.W., Boyer, M.J., and Marlay, S.K. 2011. Corn growth and development. Iowa State Univ. Ext. PMR 1009.

Aylor, D.E. 2003. Rate of dehydration of corn (Zea mays L.) pollen in the air. J. Exp. Bot. 54:2307-2312.

Fonseca, A.E. and Westgate, M.E. 2005. Relationship between desiccation and viability of maize pollen. Field Crops Res. 94:114-125.

Pilar Herrero, M. and Johnson, R.R. 1980. High temperature stress and pollen viability of maize. Crop Sci. 20:796-800.