The never-ending rains and flooding of this season have provided each of you with a host of challenges along the way. The excessive moisture has led to many issues that are obvious and easily detected – compaction, nitrogen (N) deficiency, foliar diseases, weed issues, etc. However, a potential lurking issue may be just at your feet or, more importantly, just below the soil surface.

Saturated conditions during the early vegetative growth stages has led to the development of some crown rots in corn. Crown rot infections are caused by both fusarium and pythium species. These fungi enter the plant via the root system during periods of prolonged wetness, predominately between V2 and V7. Because these fungi persist in higher moisture environments, these infections are more prevalent in wetter soils, tighter clay soil textures, higher magnesium soils, and ponded areas of fields. While these infections occur early in corn development, they can persist much longer, and the visual signs are not as easily detectable until later into the grain fill period.

The crown of a healthy corn plant will be a white-green color with a firm flesh. A fusarium or pythium infected plant will have a crown that is tan or brown in color. The crown area serves as the highway in which moisture and nutrients extracted by the root system can then be mobilized into the stalk. Often, after initial infection, the plant continues to grow and develop due to the generation of new nodal and brace roots. These new roots continue to provide access to additional sources of moisture and nutrients. However, the infection continues to develop as well, and as the plant becomes more stressed due to the remobilization of nutrients during grain fill, the plant experiences premature death (PMD).

In addition to the infection, the later-planted corn will be under compounding stress this year due to the fact that daylength during the grain fill period will be shorter in September. PMD impacts yield as a result of smaller ears and lower test weight. PMD also often leads to stalk lodging or breakage at the soil level (crown region) or just above.

White fungicide seed treatments do protect against fusarium and pythium species, the treatment does not persist long enough to protect corn from these crown rot diseases. Although some hybrids are more susceptible than others, it’s important to note that currently there are no hybrids completely resistant to these fungal pathogens.

Management Strategies to Mitigate Crown Rots and PMD

For some, it may be to late to take management steps in order to avoid the impact of PMD for 2019. However, for others, fungicide applications post-tassel are still an option.

1. Fungicide treatments made between VT and late brown silk timing can help reduce the effects of PMD by reducing stress, decreasing ethylene production, and simply keeping the plant alive longer.
2. While no fungicides are completely systemic (xylem & phloem mobile), anecdotal evidence suggests fungicide applications made approximately between the V5 to V7 growth stages can help minimize crown rots and PMD. If applied later (V8 and beyond), no adjuvants containing NPE should be used with the fungicide treatment as they can lead to arrested ear development. This includes adjuvants that are within many post-emergence herbicides (Ex: Roundup PowerMAX).
3. Row cultivation on corn that’s just beginning to show crown discoloration may be beneficial. Moving soil up around the crown can also promote nodal root development and lessen the impact of early crown infection.

It comes as no surprise that a delayed planting season typically translates into a later harvest season as well. This will be a season many will likely never forget. However, I’d encourage you to make observations now and take the necessary steps to avoid prolonging the coming harvest season.

~Luke Schulte, CCA – Field Agronomist