Three-Leaf Dieback
Beginner
Scientific Names
Fusarium, Pythium, Penicillium
Identification
- Symptoms occur either before or shortly after emergence
- Young shoots and roots suddenly die off, resulting in poor stand establishment
- Three fungi are responsible:
- Penicillium occurs as a contaminant on the seed
- Pythium and Fusarium are common in most soils
- Penicillium occurs as a contaminant on the seed
Often Confused With
Wireworm
Seedcorn maggot
Fertilizer burn
Period of Activity
Plants are usually infected by die-back pathogens during the early growth stages. Infections are most common during cool, wet conditions when plants are slow to emerge and develop. Supersweet (sh2) varieties are most susceptible to three-leaf dieback.
Scouting Notes
Begin scouting when the plants are at the spike to four-leaf stage. While walking fields, look for wilted plants and/or gaps in the plant stand where the seedlings have failed to emerge. Dig around the seed trench to look for signs of decay on the roots, mesocotyl or the seed itself. Do a plant population count to determine if re-seeding is necessary.
Thresholds
None established. Fields with a plant population less than 11,000 plants per acre may require re-planting.
Advanced
Scientific Names
Fusarium, Pythium, Penicillium sp.
Identification
Symptoms occur either before or shortly after emergence. Infected seedlings appear stunted and weak. As the disease progresses the plants become yellow and wilted. Brown spots develop on the mesocotyl and the infection quickly spreads to the growing point. The young shoot and roots suddenly die off, resulting in poor stand establishment. Several different fungi are responsible: Penicillium occurs as a contaminant on the seed, whereas Pythium and Fusarium are common in most soils.
Often Confused With
Wireworm
Seedcorn maggot
Fertilizer burn
Biology
Pythium fungi are present in most agricultural soils, and are able to infect a wide range of crops. Pythium oospores are able to survive in dry soils for long periods of time, becoming active when the appropriate environmental conditions exist. Pythium also produces zoospores which are able to “swim” to the root surface, rapidly colonizing young roots.
Penicillium and Fusarium infections are spread to the kernels during harvest and may continue to survive during storage. Most sweet corn is produced in arid regions, where the risk of infection is reduced.
Period of Activity
Plants are usually infected by die-back pathogens during the early growth stages. Infections are most common during cool, wet conditions when plants are slow to emerge and develop. Supersweet (sh2) varieties are most susceptible to three-leaf dieback.
Scouting Notes
Begin scouting when the plants are at the spike to four-leaf stage. While walking fields, look for wilted plants and/or gaps in the plant stand where the seedlings have failed to emerge. Dig around the seed trench to look for signs of decay on the roots, mesocotyl or the seed itself. Do a plant population count to determine if re-seeding is necessary.
Thresholds
None established. Fields with a plant population less than 11,000 plants per acre may require re-planting.
Management Notes
- Planting into suitably warm soils and ensuring rapid germination is the best protection against three-leaf dieback.
- Use fungicide-treated seed and plant only once the soil has reached an appropriate soil temperature based on the type of sweet corn grown. Supersweet (sh2) varieties will not germinate at soil temperatures lower than 18°C (65°F). Sugar enhanced (se) varieties require temperatures greater than 16°C (60°F). Under cool soil conditions, plant only normal (su) varieties.
