Are crown rot and PMD looming in corn?

By Luke Schulte, Beck’s Hybrids

As I write this, the rain continues to inundate many corn and soybean fields throughout the state. Unfortunately, many Ohio farmers will likely find their corn crop in one the following scenarios:

1. Those that could plant early but have since endured saturating rains.
2. Those that were unable to plant early, but due to the calendar, may have had to push field conditions rather than wait for an ideal planting situation.

Either scenario presents the increased potential for the corn root system to be exposed to infections that challenge staygreen and natural maturation.

Crown rot in corn results in plants that prematurely die. Not only does this affect final yield but often standability is impeded as well. Crown rot is caused by various species of Fusarium and Pythium, which are commonly found in our soils. The crown area serves as the “highway” for transporting water and nutrients from the roots to the remainder of the plant. These fungal pathogens enter the root system when conditions are persistently wet between the V2 and V7 growth stages. The disease initially causes the internal crown tissue to have a brown, discolored appearance compared to the normal white-green coloration of a healthy plant. Externally, infected plants often don’t show symptoms or have only minimal evidence of infection. However, if infection is significant, plants may appear stunted or even exhibit browning of the lower leaves. Infected plants often appear to outgrow the infection due to the generation of additional nodal roots. These newly formed roots provide access to additional moisture and nutrient reserves and the plant survives, albeit with a reduced vascular system.

Despite the fact that the plant appears to recover, the infection continues to persist and develop. This infection disrupts the transport of moisture and nutrients from the roots throughout the plant. Plant stress is compounded by nutrient remobilization throughout the grain fill process. Ultimately, the plant succumbs to a premature death (PMD). The impact of PMD typically results in smaller ears and lower test weight. It also often leads to stalk lodging at the soil level (crown region) or just above.

Wet soils during the early vegetative stages (V2-V7) favor infection. Compacted soils, tight-textured soils, greater than 20% base saturation magnesium levels, and sidewall compaction are all situations conducive to infection.

Since many times external symptoms can be lacking, awareness of field conditions and weather patterns is critical to identifying crown rot in the field. If conditions have been favorable for infection, early scouting becomes more critical. While there are no hybrids immune to crown rot, hybrids do vary in susceptibility. To assess for crown rot, dig up a plant and split the stalk down the middle to visually detect discoloration of the crown area. Keep in mind, not all plants may be infected; therefore, it is important to split multiple plants in a given area. While the current commodity market does not welcome unexpected crop inputs, mitigation expenses will provide a benefit as well as a positive return on investment when infection is identified.