Crown rot in corn is caused by various species of Fusarium and Pythium, which are commonly found in soils throughout most corn-growing regions in the United States.

Crown rot in corn is caused by various species of Fusarium and Pythium, which are commonly found in soils throughout most corn-growing regions in the United States. The crown of the corn plant is the top of the root system, where the stalk begins. It contains vascular tissue critical for transporting water and nutrients from the roots to the rest of the plant. Conditions that cause crown rot, wet conditions, and tight-textured or compacted soils are more prevalent in the Eastern Corn Belt than in areas further west.

Infection occurs when pathogens enter via the root system of the corn plant from the V2 to V7 growth stages after the seed treatment fungicides have dissipated. The disease initially causes the internal crown tissue to have a brown, discolored appearance compared to the normal white-green coloration of a healthy crown. 

There are few external symptoms of early infections. Where external symptoms are present, plants may be stunted or exhibit symptoms resembling nutrient deficiencies like yellowing or even browning of the lower leaves. Plants may also appear wilted or even die with severe early infections. Infected plants often outgrow the infection due to the generation of additional nodal roots that renew access to moisture and nutrients, albeit, with a reduced vascular system.

Symptoms during the late vegetative and early reproductive stages resemble early-season symptoms. Plants may exhibit no outward symptoms of the disease, and may appear to have grown out of any early symptoms; however, the crown infection continues to progress. When the corn plant reaches the grain fill stages, the reduced water and nutrient uptake throughout the season begins to take its toll, and continued uptake at these stages is severely limited. Plant stress is further compounded by nutrient remobilization throughout the grain fill process.

Ultimately, the plant succumbs to premature death or PMD. PMD typically results in smaller ears and lower test weights. Additionally, lodging may occur as the stalks become weak due to the infection of the crown area and require higher rates of nutrient remobilization than in a healthy plant.

FIELD CONDITIONS FOR INFECTION AND DISEASE PROGRESSION

Pathogens that cause crown rot are most prevalent in high moisture environments as wet soils during the early vegetative stages favor infection. Compacted soils, soils with tight textures, and soils containing high magnesium levels are all situations that favor disease development. Watch for disease development where waterlogged soils or ponding occurred in the early corn growth stages (V2-V7), especially in clay-texture soils. 

Once infected, PMD onset may be earlier in stress situations, like drought and high heat, where water and nutrient uptake may already be limited. Additionally, the effects of PMD may be exacerbated in late-planted corn, since shorter days following pollination challenge carbohydrate and photosynthate production throughout grain fill.

Due to the lack of early external symptoms, it is important to be aware of the weather, field conditions during the early growth stages, and hybrid susceptibility. If conditions have been favorable for infection, it is important to scout early. To assess crown rot, dig up a plant and carefully split the stalk down the middle. The crown will express the earlyseason symptoms previously discussed. Crown rot may be more prevalent in persistently wet areas of fields, making those plants more prone to infection. Additionally, not all plants may be infected, and adjacent symptomatic and asymptomatic plants are common.

 Strobilurin (QoI) fungicides have limited efficacy on some Pythium
species. It is not possible to determine the causal pathogen of crown rot
without lab testing, so choose a fungicide with an alternative mode of
action or multiple modes of action.

Row cultivation on corn that is beginning to show infection may be beneficial as it pushes the soil around the crown up and stimulates nodal root development. Improving drainage and minimizing compaction will also help to reduce the high moisture areas that are conducive to infection. Harvesting fields early that are known to be infected will help to minimize losses from lodged corn, which may be greater than the additional drying costs associated with early harvest.