Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
Over the past week, post-emergent damping off of corn has been present across the state. In most cases, this damping off has been caused by Pythium sp. Symptoms can include stunted, slower growing plants, to severely infected, dead plants (Figure 1). Infected plants typically have brown, rotted roots and mesocotyl. In severely infected plants, the top of the plant may be completely separated from the root system, resulting in plant death (Figure 2). Damping off from Pythium is common in low field areas that hold more moisture, but wet, cool spring conditions have favored development across entire fields this season.
Figure 1: Damping-off of corn caused by Pythium
Pythium is a soilborne fungal-like organism that is able to survive in the soil for many years as oospores. Under favorable environmental conditions, the oospores are able to germinate and produce small zoospores that swim in soil water following root exudates to infect emerging seedlings. Once root systems have developed, seedlings can usually survive mild to moderate Pythium infections. Seed treatments with oomycete activity can provide some protection for 10-14 days after planting, and can be helpful for improving seedling emergence and reducing pre-emergent damping off. This year most issues have occurred as post-emergent damping-off. Multiple species of Pythium are able to infect corn, with each species having a different optimal temperature. We are currently collecting samples to identify which species have been involved in infection this year.
Figure 2: Corn seedling with damping-off caused by Pythium