Poinsettia Insights

Nancy Rechcigl

Known for their vibrant colors and festive spirit, poinsettias are the crown jewel of the holiday season. However, for ornamental greenhouse growers, poinsettias are one of the most time-sensitive and challenging crops. As growers move past the halfway point of the production cycle, greenhouse teams are entering a critical late-season period where attention to detail can make or break the quality and attractiveness of the finished crop. 

This season has brought a variety of challenges—from unexpected disease pressure to subtle pest outbreaks—that have kept growers on high alert and underscored the need for adaptive management strategies.

Poinsettia canker
At this stage of production, with the fundamentals well-established, growers are typically focused on managing whiteflies. But this year, disease pressure has emerged as the most significant threat to poinsettia plant health. Poinsettia cankers have been observed across multiple crops, caused by two notable bacterial pathogens:

• Curtobacterium flaccumfaciens pv. poinsettiae (formerly known as Corynebacterium poinsettia) is a gram-positive bacterium that often develops slowly and can remain latent until later stages of production.
• Pseudomonas viridiflava, responsible for “Greasy Canker,” is a gram-negative bacterium first reported in poinsettias in 1979. This pathogen produces elongated, dark streaks on stems that appear greasy under high humidity, typically at sites of injury, such as pruning wounds or leaf removal points.

While Curtobacterium is typically blamed when we see cankers, this year diagnostic tests have indicated Pseudomonas “Greasy Canker” is also present. Both pathogens can cause severe blight on leaves, buds and bracts, rendering crops unsaleable if left unchecked.

Poinsettia with Pseudomonas viridiflava.

While disease progression may slow under lower humidity and cooler temperatures, both pathogens require prompt action. Management strategies include removing and discarding infected plant material, thoroughly sanitizing benches and greenhouse surfaces, and applying a copper-based product in rotation with a fungicide solution, such as Postiva fungicide.

Postiva delivers broad-spectrum, long-lasting protection against challenging ornamental diseases such as these. Its unique active ingredients are quickly absorbed, forming a rainfast barrier that prevents new infections and slows disease spread, helping you maintain crop quality through the late season.

Powdery mildew
Powdery mildew remains a persistent challenge in late-season poinsettia production, rapidly developing on leaves, stems and bracts. Early symptoms appear as small, chlorotic spots that quickly expand into white, powdery fungal colonies, reducing photosynthesis, distorting plant tissues and diminishing overall crop quality. Over time, affected leaves yellow, brown and drop, and if left unchecked, the disease can spread rapidly through the canopy, severely impacting marketability.

This pathogen is particularly problematic for poinsettia crops grown in cooler regions and, unlike many foliar diseases, can thrive even under relatively low humidity. For this reason, vigilant scouting is critical for early detection and control. 

Preventive fungicide applications are also essential. Periodic treatments with effective products such as Mural fungicide help keep poinsettias protected from start to finish, even during shipment. Mural delivers broad-spectrum control against tough foliar and root diseases, including powdery mildew. With strong systemic activity and reliable performance at low use rates, it’s a versatile tool to maintain crop health and quality late in the season.

Pseudomonas viridiflava streaking. 

Botrytis
No poinsettia season is free from the threat of Botrytis, a persistent late-season threat that can impact crops from propagation through shipment. This disease thrives in cool temperatures and high humidity, producing light brown, V-shaped spots on foliage and bracts. Its presence is easily recognized by the abundant gray, fuzzy spores that develop under humid conditions. Once established, Botrytis can spread quickly throughout the canopy, affecting both living and senescent tissues and compromising overall plant quality.

Effective late-season management relies on reducing relative humidity through careful heating and venting, combined with timely applications of protectant fungicides such as Palladium fungicide. With its dual active ingredients, Palladium delivers systemic protection against key foliar and stem diseases like Botrytis, offering preventive and curative control plus up to two weeks of residual activity.

Lewis mites
This year, outbreaks of Lewis mites (Eotetranychus lewisi) have once again been observed in some poinsettia crops. These mites are more difficult to detect than two-spotted spider mites because of their smaller size and the subtle damage they cause. Like spider mites, they feed primarily on the undersides of foliage, causing faint stippling that’s far less noticeable. Over time, affected leaves turn chlorotic, which can easily be mistaken for nutrient deficiency.

Lewis mite on poinsettia. 

Unlike spider mites, Lewis mites produce little to no webbing and their bodies display several small spots rather than the two large spots typical of spider mites, making scouting even more critical. Careful examination of the undersides of leaves, especially those showing early chlorosis, is essential for early detection. Prompt action allows growers to control populations before they cause significant crop injury.

For management, applications of Avid 0.15EC miticide/insecticide are highly effective and safe to use, even on bracts in color. Avid also delivers broad control of other key mites and insects, helping reduce tank mixes and simplify greenhouse pest management.

Integrated solutions for late-season success
By integrating preventive products early and maintaining vigilant cultural practices, such as sanitation and regular scouting, you can protect poinsettias when they’re the most vulnerable and ensure strong, market-ready crops through the late season. 

In addition to high-performance products, Syngenta provides industry-leading technical support to help you optimize crop management from propagation through shipment. For detailed guidance on late-season poinsettia pest management, including recommended use rates and application strategies, visit GreenCastOnline.com/Ornamentals. GT

Nancy Rechcigl is Technical Field Manager for Syngenta Ornamentals. 

Performance assessments are based upon results or analysis of public information, field observations and/or internal Syngenta evaluations. All photos are either the property of Syngenta or are used with permission. 

© 2025 Syngenta. Important: Always read and follow label instructions. Some products may not be registered for sale or use in all states or counties and/or may have state-specific use requirements. Please check with your local extension service to ensure registration and proper use. Avid®, GreenCast®, Mural®, Palladium®, Postiva® and the Syngenta logo are trademarks of a Syngenta Group Company. All other trademarks are the property of their respective third-party owners.