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There are numerous stalk rots that affect corn in mid- to late-season. Weather, nutrition and genetic disease tolerance all play major parts in the disease cycle. Plants move nutrients from the stalks to the ears during grain fill. High yields mean heavier ears. These two phenomena combined can make stalk quality issues a problem even in very high-yielding areas.

Disease: Anthracnose

• Signs and Symptoms: Stalk: black, shiny lesions, often blotchy in appearance, easily crushed. Nodes: Discolored Pith: Disintegrated. Plant: Causes top dieback and premature death 
• When to Scout: R5 - R6
• Conditions Conducive for Infection: Cloudy days with high humidity; plant stress following pollination; reduced tillage.
• Management Strategies: Plant hybrids with some resistance; reduce plant stress and wounding; rotate crops 

Disease: Bacterial Stalk Rot

• Signs and Symptoms: Stalk and Rind: darkbrown, water-soaked lesions; soft, slimy tissue; foul odor; twists during lodging. Plant Tips: Slimy and rotten; may die prematurely. 
• When to Scout: V2 - R6
• Conditions Conducive for Infection: Hot, humid periods 
• Management Strategies: Avoid overhead irrigation with pond/surface water; provide adequate field drainage; avoid common stressors, including insect damage 

Disease: Charcoal Rot

• Signs and Symptoms: Pith: disintegrated and covered in silver-black fungal structures (“charred” appearance). Stalk and Roots: May be covered in black fungal structures. 
• When to Scout: R5 - R6
• Conditions Conducive for Infection: Hot and dry conditions (soil temperatures >90°F), especially near plant maturity; corn on corn rotations
• Management Strategies: Irrigate during hot, dry seasons; avoid common plant stressors (heavy foliar disease, nutrient imbalances, etc.) 

Disease: Diplodia Stalk Rot

• Signs and Symptoms: Stalks: brown/black fungal structures embedded in the rind (not easily scraped off) on either side of nodes; can be easily crushed. Pith: disintegrated. But vascular bundles remain intact 
• When to Scout: R5 - R6
• Conditions Conducive for Infection: Warm, moist conditions 2-3 weeks following pollination; corn on corn rotations
• Management Strategies: Rotate crops; plant hybrids with some resistance; till infected residue into soil; avoid plant stress and wounding 

Disease: Fusarium Stalk Rot

• Signs and Symptoms: Pith: disintegrated with salmon-pink discoloration. Leaves: dull green. Can exist on healthy plants and become problematic when the weather changes 
• When to Scout: R5 - R6
• Conditions Conducive for Infection: Dry conditions before silking followed by warm, wet conditions after silking (80-100°F); environmental or physiological stress
• Management Strategies: Reduce plant stresses; control foliar diseases; provide adequate field drainage; avoid high-nitrogen, low-potassium soils 

Disease: Gibberella Stalk Rot 

• Signs and Symptoms: Pith: disintegrated with pink-red discoloration. Stalk: small, black fungal structures (easily scraped off)
• When to Scout: R5 - R6
• Conditions Conducive for Infection: Warm, moist conditions during reproductive growth; environmental or physiological stress; insect feeding; alternate/overwintering hosts like wheat, rye, barley
• Management Strategies: Avoid wheat-corn rotations; avoid plant stress and wounding 

Disease: Pythium Stalk Rot

• Signs and Symptoms: Pith and Rind: soft, brown, and water–soaked. Leaves: green even after lodging. Stalk: twists during lodging
• When to Scout: V2 - R6
• Conditions Conducive for Infection: Hot, wet, and humid conditions
• Management Strategies: Avoid overhead irrigation with pond or other stagnant water; provide adequate field drainage; avoid common plant stressors 

Disease: Cannibalization

• Signs and Symptoms: Stalk: hollowed out. Pith: disintegrated, soft. Leaves: usually show N deficiency
• When to Scout: R5 - R6
• Conditions Conducive for Infection: Wet conditions favoring N loss OR dry conditions restricting N uptake
• Management Strategies: Apply N later in the season; reduce saturated soils with drainage; irrigate in dry conditions 

Disease: Physoderma Stalk Rot

• Signs and Symptoms: Stalks: Black rings at lower nodes; easily snapped at nodes. Note: same pathogen that causes Physoderma Brown Spot on leaves 
• When to Scout: V5 - V9
• Conditions Conducive for Infection: Wet conditions during V5 to V8 and higher. Spores can live up to two years in the soil
• Management Strategies: Tillage and crop rotation  

Stalk Cannibalization:

In general, well-fed plants tend to be healthier and have fewer disease issues. Plants with inadequate soil fertility will cannibalize the stalk, leaving the stalk more prone to infection from stalk rots. Stalk cannibalization can mimic stalk rot disease because symptoms are weakened stalks and lodged corn. Adequate N and K are critical for stalk integrity especially in years with above average rainfall and consequently higher disease pressure. High kernel set triggers the need to pull nutrition from other parts of the plant to fill the kernels. High yield levels can increase stalk cannibalization and lead to higher lodging.

Above: Stalk pinching due to stalk cannibalization without the presence of stalk rot diseases.
Photo by Mike Hannewald

Residue Management:

Many common stalk diseases can overwinter on corn residue or other cereal crop residues. Heavy tillage can help to manage disease inoculum.

Harvest Order:

Work with your trusted Beck’s advisor to scout prior to harvest to get a plan in place for harvest priority. Often the benefits of early harvest and the use of drying systems outweigh the headaches and yield loss of allowing corn to dry in the field and risk stalk rots.

Planning for the Future:

Select hybrids resistant to common stalk rots, keep in mind ratings may not be available for all common stalk rots. Planting a wider range of maturities can also spread out maturity and help to manage risk of infection opportunities for your whole operation. Traited hybrids provide good protection against insect pests and reduce overall stress during the growing season. Many stalk rots can be somewhat opportunistic on fields already compromised by physiological or environmental stressors.

For a video explaining how to evaluate stalk quality in your fields, click here. 

 

Click here for a downloadable version of this Agronomy Talk update