How Poinsettia Diseases Can Ruin the Holiday

Poinsettia are holiday decorations in public and personal spaces. No holiday décor is complete without at least one. However, numerous plant diseases can act as a Grinch to steal holiday cheer. Proper plant selection and maintenance are important for a disease-free poinsettia that will last well into the New Year.

Poinsettia Selection

Inspect all plant parts prior to purchase. Development of disease symptoms may occur over long periods of time. Early symptoms are easy to overlook as they are often small and underdeveloped.

Assess bracts (colorful, flower-like structures) and leaves for spots and damage. These spots can be the start of diseases, such as scab and Botrytis blight. Both of these diseases can cause tan to gray-brown spots on bracts and leaves (Figure 1) and ultimately result in plant dieback and defoliation.

Stems can also become infected by disease-causing pathogens. Bacterial diseases (such as, bacterial soft rot and bacterial canker), as well as, fungal diseases (Botrytis blight, scab, and Rhizoctonia root and stem rot) can damage stems. Lesions often develop on stems near the soil line (Figure 2). Since stem infections limit the plants ability to move nutrients and water throughout the plant, symptoms such as wilting, dieback, and defoliation may be observed.

If plants can be removed from the pot, inspect roots for damage and decay. Pythium root rot, black root rot, and Rhizoctonia root and stem rot can all impact roots. They result in blackened, fragile roots that are unable to support the plant (Figure 3). When roots are damaged, upper plant parts cannot be supported, resulting in wilting and dieback.

Figure 1: Leaf spot symptoms caused by scab. (Photo: John Hartman, UK)

Figure 2: Stem lesion caused by bacterial stem canker disease. (Photo: Cheryl Kaiser, UK)

Figure 3: Blackened, rotted roots as a result of black root rot disease. (Photo: Cheryl Kaiser, UK)

Plant Maintenance & Disease Management

  • Maintain plant health and vigor with proper nutrition, light, and watering practices.
  • Water at the base of the plant to avoid splash.
  • Remove plants from decorative pot covers. These may hold water.
  • Drain saucers immediately after watering. Do not allow plants to sit in water. Overly wet soils can lead to root rot disease issues.
  • Remove and destroy any leaves or plant parts that are dead, discolored, or deteriorating.
  • Avoid crowding. Space plants to increase air circulation.
  • Dispose of any plants that show disease symptoms.
  • Once plants become infected, management options are limited.
    • Root and stem rots cannot be treated or cured.
    • Leaf spots and blossom symptoms can be managed by removing infected plant parts and maintaining plant health. The life the plant can often be extended through the holiday season.
    • If disease is severe, the plant should be discarded, especially in situations where additional plants are at risk for infection.

Additional Resources

  • Poinsettia Diseases (PPFS-GH-06)
  • UK Plant Pathology Extension Publications (Link)

 

By Kim Leonberger, Extension Associate and Nicole Ward Gauthier, Extension Plant Pathologist

 

 

 

Posted in Ornamentals