Pythium, Rhizoctonia and Fusarium species
Symptoms
Figure 1 - Initial Pythium infection with sunken light tan tissue on hypocotyl and wilting.
Figure 2 - Initial Rhizoctonia root rot lesions are sunken, reddish brown and irregular shaped. Wilted plant is shown also.
Figure 3 - Initial Fusarium root rot lesions are reddishbrown and linear, while older lesions cover the roots and
hypocotyls.
Figure 4 - Fusarium wilt brown to orange discoloration of roots and hypocotyl. Discolored streaks extend upward in water conducting tissue (vascular bundles) to yellow, wilted leaves.
Factors favoring
- Contaminated seed and/or infested debris from previous seasons
- Low quality and/or old seed (more than 2 years after certification)
- Cool, wet conditions after planting, and/or factors contributing to slow emergence
- Soil compaction which reduces root growth, and crop rotation less than 3 years
- Cool temperatures with daily highs less than 77ºF [25ºC] favor Rhizoctonia and Pythium before flowering, and greater temperatures after flowering favor symptom onset of Fusarium diseases
Figure 1 - Pythium
Figure 2 - Rhizoctonia
Figure 3 - Fusarium
Figure 4 - Fusarium
Additional Resources
Photo credits
H. F. Schwartz, Colorado State University