Stalk and root rot diseases of corn are a common problem and appear at varying degrees of severity each year. Most stalk rots are caused by opportunistic pathogens that infect the plant after being weakened by preexisting plant stress. Stressors that predispose plants to stalk rot infection include:
- Nutrient deficiency
- Saturated soils
- Droughty soils
- Soil compaction
- Foliar leaf disease
- Leaf area loss due to hail or insect damage
How Plant Stress Can Open the Door to Stalk Rot Pathogens
- Plant stress often reduces photosynthesis causing the plant to pull carbohydrates from the root and lower stalk area to support grain fill.
- The weakened stalk area becomes more vulnerable to colonization by stalk rot pathogens.
- Weakened vascular tissue in the stalk can no longer transport water or carbohydrates effectively, resulting in premature death and shortening of the grain fill period.
- Yield may be impacted by both a reduction in grain density and potential harvest losses due to weakened stalks.
- Upon premature plant death, secondary pathogens begin to colonize dead plant material, making diagnosis of causal pathogens even more difficult.
The Importance of Identifying Stalk Rot Pathogens Prior to Harvest
Identifying stalk rots in the field can be challenging because symptoms often appear late in the season and may not be obvious until damage has already occurred. Growers should watch for premature plant death, especially when individual plants turn brown while neighboring plants remain green. Discoloration at the lower nodes, ranging from gray to dark brown or black, is another common indicator, and internally affected stalks may appear to be hollow or shredded. The following descriptions can help distinguish between specific stalk rot you may be seeing in your field:
Timing Tips for Stalk Rot Scouting
Scout fields in late August through September using push or pinch tests to identify weakened stalks and prioritize at-risk fields for harvest before lodging occurs. Two simple field checks can provide a clearer picture of stalk health. The push test involves leaning plants to about a 30-degree angle and observing whether they turn upright, failure to do so indicates compromised integrity. The pinch test, which involves squeezing the lower internode, can also reveal weakness if the stalk collapses easily. Regular scouting in late august through September can prioritize fields before harvest begins.
Management Tips for Stalk Rot
- It is important to understand which pathogen caused the stalks to rot in order to manage for that pathogen in future growing seasons.
- It is difficult to predict areas of disease pressure due to variability of environmental conditions year by year, making management complex.
- Hybrids vary in susceptibility, so ask your seed advisor or agronomist for information on hybrid susceptibility for fields with known history of the disease.
- Crop rotation and tillage may help reduce disease development and pressure.
- Minimize plant stress through recommended populations, adequate soil nutrients, and proper soil drainage to help reduce the risk of stalk rots.
- To help protect against diseases and insects early in the season that can contribute to stalk and crown rots, consider using a seed treatment such as CruiserMaxx® Vibrance® Corn seed treatment.
- A fungicide application of Trivapro® or Miravis® Neo fungicide at VT or R1 may reduce foliar disease severity, maintain photosynthesis during grain fill, and improve overall plant health.
- Scout fields in late August through September to assess stalk strength and determine which fields should be harvested first.