Description and Symptoms
These stalk rots are not common in Iowa. They can occur any time during the season, particularly if conditions are very wet. They cause decay of the first internode above the soil. The rind and the pith become soft, brown, and water-soaked. Decayed tissue sometimes has a strong odor. The stalk typically twists and falls over, but the plant may remain green for several weeks because the vascular tissue is not destroyed. Plants affected by bacterial stalk rot have a foul odor. Some hybrids are more susceptible than others.
The best time to scout for pythium stalk rot is during extended periods of hot, wet, or very humid weather. Incidence may be higher with overhead irrigation, especially when pond or stagnant water is used. Pythium stalk rot is rarely seen in Iowa and can cause premature death at any growth stage.
• Target fields that have had significant foliar disease.
• Target hybrids with low stalk rot and/or standability scores.
• Evaluate at least 100 plants per field (20 plants in 5 locations).
• Use the "push test" or the "pinch test" to determine standability. If 10 to 15 percent of plants lodge or are rotted, schedule an early harvest.
Photo by Alison Robertson