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A wetter-than-normal season in the Midwest is starting to be reflected in corn growth in southern Iowa, and, according to Iowa State University (ISU) plant pathologist Alison Robertson, “It seems to be getting worse.”
Within the past week, several cases of corn seedlings with symptoms of post emergent damping off have been reported. Corn planted in May that should be at a V3 to V4 growth stage, are only measuring at stage V1 to V2 upon arriving at the ISU Plant and Insect Diagnostic Clinic.
The stunted growth is directly related to soil that is heavier, wetter and has a higher clay content, which means that other areas experiencing abnormally high precipitation will likely see similar effects. Mark Carlton, Field Agronomist in Iowa’s southern counties, said that corn planted around May 15 is at the highest risk due to immediate rainfall, compared to seedlings that received four to five dry days first.
Carlton said that as much as ten to 15 percent of corn in southern Iowa is being affected by damping off. Those fields being severely affected will suffer a 40 to 50 percent loss in yield potential from replanting.
“This is the third or fourth year in a row we’ve seen significant rates of damping off,” Carlton said. The two biggest reasons for the increase are soil pathogens that defeat fungicides, and rotation no longer serving as a successful control method.
The pathogen responsible this year for damping off in southern Iowa fields is known as Pythium, which thrives in soil conditions that are cool (below 55 F) and saturated. Fusarium, anhydrous, ammonia injury, wireworms and cold injury may also play a role. Seedling susceptibility to fungal infection increases the longer the seed sits in the soil, and the more stress germinating corn undergoes.
Survival of young corn seedlings depends on a healthy kernel and mesocotyl, which should stay white and firm through growth stage V6. The developing corn seedling relies on the mesocotyl as a “pipeline” of nutrients from the kernel and seminal roots, to the seedling stalk and leaf tissues. Damage to these areas before the nodal root system is mature results in stunted, weak or even dead seedlings.
Though there is no current prevention for damping off, Carlton suggests applying a fungicide to crops and improving drainage as much as possible.