Figure 1. Corn plants prematurely killed due to stalk rot. Notice the tan color of the stalks on the left compared to the health stalk with still green roots on the right. Courtesy: Emmanuel Byamukama
Stalk rots are one of the late season diseases corn growers need to be aware of. Stalk rots can lead to lodging and lodged plants pose a challenge to corn harvesting. Areas which experienced heavy rains and nutrient leaching (like nitrogen) may find stalk rots as a common problem this year. With South Dakota high fall winds, it is important to scout corn fields for stalk rots and then make corn harvesting decisions based on findings in order to avoid heavy corn lodging.
Types of Stalk Rots
The most common stalk rot found while scouting corn was Fusarium stalk rot (caused by Fusarium spp). Plants with this stalk rot tend to have stalks with no rind discoloration but plants die prematurely (Figure 1). When the infected plants stalks are split open and shows disintegrated pith which may or may not be discolored. Other stalk rots found include Gibberella stalk rot (caused by Gibberella zeae) and anthracnose stalk rot (caused by Colletotrichum graminicola) (Figure 2). Plants with Gibberella stalk rot tend to have pink discoloration of the pith and black raised spots outside the lower nodes. Plants with anthracnose stalk rot have a shiny black color on the outer stalk and can be found on the lower nodes and top nodes late in the season.
Figure 2. Common stalk rots: A) Gibberella stalk rot (notice the pink discoloration and disintegration of the pith), and B) Anthracnose stalk rot (notice the black discoloration of the rind). Courtesy: Emmanuel Byamukama
Early Harvesting Considerations
While stalk rots cannot be managed at this point in the season, a few things can be done to minimize the grain loss from symptomatic plants. Scout the field to assess the level of stalk rots. A push method, where a corn plant is pushed gently to about 45° to the ground, should be used. Plants which spring back up have a healthy stalk and plants that crumble and don’t return may have stalk rot (Figure 3). The push method should be done on at least 50 plants (10 plants for 5 random stops within the field) and if 10% or higher of the plants crumble, early harvesting should be done to avoid lodging.
Figure 3. Assess corn stalk rot by the push test. If the plant does not return to an upright position, it may have stalk rot. Courtesy: Emmanuel Byamukama
Managing Stalk Rots for Future Seasons
- Practice crop rotation to break the disease cycle. All stalk rot pathogens survive on corn residue, therefore rotations will reduce inoculum in the field.
- Select hybrids with good ratings for stalk rot resistance/tolerance.
- Avoid high planting population.
- Maintain good soil fertility and improved soil drainage to reduce risk for stalk rots to develop.