Even with adequate moisture and timely silking, heat alone can desiccate silks so that they become non-receptive to pollen. While this is a bigger problem when humidity is low, it is apparent that it is happening this year, especially on hybrids that silk quite early relative to pollen shed. Even with dew points in the 70s, when temperatures reach the high 90s to the100s, the heat can still desiccate silks and reduce silk fertility.
Heat also affects pollen production and viability. First, heat over 95°F depresses pollen production. Continuous heat, over several days before and during pollen-shed, results in only a fraction of normal pollen being formed, probably because of the reduced sugar available. In addition, heat reduces the period of pollen viability to a couple hours (or even less). While there is normally a surplus of pollen, heat can reduce the fertility and amount available for fertilization of silks. It’s been shown (Herrero and Johnson, see Resources) that prolonged exposure to temperatures reduced the volume of pollen shed and dramatically reduced its viability.
For each kernel of grain to be produced, one silk needs to be fertilized by one pollen grain.
- Senescence and Receptivity of Maize Silks by Paolo Bassetti and Mark Westgage, Crop Science, 33: 275-278. Abstract
- High Temperature Stress and Pollen Viability of Maize by Maria Pilar Herrero and R.R. Johnson, Crop Science 20: 796-800. Abstract