Fainting “Freedom Red”? Wilting “Whitestar”? Potential causes of Poinsettia collapse, solutions, and the importance of testing.

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Wilting  of a poinsettia plant on a bench of otherwise healthy plants could be Pythium root rot. But then again, it might not…

From now until mid-November is when you’ll most likely see plant losses in poinsettia due to severe wilting. These losses can be considerable: anywhere from 2-15% in Niagara operations in past years.  Pythium may be considered the most “likely” culprit in Poinsettia in this area, but this isn’t always the case, and misdiagnosis can mean wasted fungicide applications. Read on for a list of likely suspects and appropriate control measures.

Common Culprits:

The below chart can help serve as a guide to what could be causing your poinsettias to wilt on the bench.  This poinsettia diagnostic key from NC State may also help narrow down the issue.  Unfortunately, many root rot diseases have extremely similar symptoms, and many are almost impossible to properly differentiate correctly without further testing.

Pathogens like Pythium and Fusarium – being opportunistic and ever-present in the greenhouse environment – can also commonly co-occur with other diseases, masking what actually started the problem.

In all cases, once you suspect one of these diseases, it’s best to have the pathogen confirmed at least once by DNA analysis by sending it Lab Services at the University of Guelph or another facility, or by having an OMAFRA agent send in samples for you (a free service if the answer isn’t readily apparent after an on-farm visit).

Timing
Symptoms*
Likely Culprit
Response**
Can occur at any stage of production but may not show up until November
The base of infected stems appear soft and wet. Roots are brown and water soaked. Under dry conditions, the internal pith of the lower stem is brown when cut; the stem has a gray canker.
Phytophthora root/stem rot (Phytophthora nicotianae or drechsleri)
Rogue infected plants. Clean tools, keep hose ends off the ground. Apply a fungicide to protect plants, e.g. Truban (etridiazole), Torrent (cyazofamid). Control of this pathogen is difficult; exclusion is key; consider treating water source.
Can occur at any stage of production
Early in the season, rooted cuttings are stunted, yellow, and wilting. Roots are dark brown and can look “wet”; the outer layers of root tissue strip off leaving a bare strand of inner vascular tissue exposed. Later in the season, lower leaves yellow and drop; plants are stunted.
Pythium Root Rot (various Pythium species)
Rogue infected plants. Clean tools, keep hose ends off the ground. Do not over-water or over-fertilize plants. Apply a fungicide to protect plants: e.g. Subdue Maxx (metalaxyl) or Truban (etridiazole)
Often kills plants immediately after transplant; if disease progresses slowly than may not die until November
Early in the season, cuttings wilt and yellow. Roots are rotted. Lower stems below ground may have a shredded appearance. Later, lower leaves may yellow and fall off; plants flower prematurely, and die. Sunken dark brown cankers on stem may reach slightly above soil line. Brown lesions visible on roots.
Rhizoctontia wilt (Rhizoctonia solani)
Rogue infected plants. Clean tools, keep hose ends off the ground. Do not over-fertilize. Apply a fungicide to protect plants, e.g. Heritage (azoxystrobin).
September to October, usually
Plants may be stunted; will wilt suddenly and die; may defoliate. Roots and crowns may develop brown-black discoloration and become soft. Rotted areas may develop cream-orange, wet-looking, spore masses.
Fusarium wilt (Fusarium oxysporum)
Rogue infected plants. Clean tools, keep hose ends off the ground.  Apply a fungicide to protect plants, e.g. Senator (thiophanate methyl) or Medallion (Fludioxonil).
Late in Season under cooler weather conditions
Roots turn black. Plant wilt. Longitudinal splits form at the stem base at and below soil line. Leaves yellow and fall.
Black Root Rot (Thielaviopsis basicola)
Rogue infected plants. Clean tools, keep hose ends off the ground.  Apply a fungicide to protect plants, e.g. Senator (thiophanate methyl) or Medallion (Fludioxonil).
* Symptom list adapted from Penn State, NC State, and Texas A&M Extension
** Other fungicides may also be effective; these are only some suggestions. Always check the label before applying.

Phytophthora crown rot. The pathogen is Phytophthora drechsleri, which causes a root rot that may extend upwards into the lower stem. It is not possible to distinguish this injury from that caused by Pythium aphanidermatum, which is also commonly found on poinsettias. Photo and info courtesy of Cornell Cooperative Extension.

 

Stem lesion on a Rhizoctonia-infested plant.

 

Other problems not included in the above chart, like leaf yellowing, curling or overall stunting, are likely due to nutrition issues.   Check out this previous post on poinsettia nutrition and ask yourself if the problem is widespread (likely nutritional) or with a more patchy distribution (diseases tend to hit a group of plants in the crop).

Poinsettia Nutrition Infographic

Common nutritional problems of poinsettia. Problem photo credits: Brian Whipker (NC State University).

Planning for Next Year: Prevention

Experiencing significant losses from one of the above culprits this year?  Or have a smaller issue year after year that just won’t go away? Then it’s likely time to consider a preventative application on the entire crop next year.  Diseases like Pythium and Fusarium are especially hard to control once symptoms actually appear.  Getting on top of the problem early is always a better choice, both efficacy-wise and pocket-book wise.

Drenching fungicides while the poinsettias are still in the trays is an effective option.  Although some growers are hesitant to apply fungicides to poinsettia at this stage due to fears  this may delay rooting (especially when grown in Oasis strips), this appears to be unfounded for most fungicides (see this study).  My own studies in a commercial poinsettia crop are currently showing good disease control and good root quality with this method.  I’ll report back more on this in December.

Microbial fungicides like Actinovate, Cease, PreStop, Rootshield, Taegro and Trianum (drenched on cuttings, and then again at potting) are also a potential option. The beneficial organisms they contain occupy the space where pathogenic fungi would normally grow, and also actively fight them off.  They can also help improve rooting.  

Microbial fungicides also tend to be more “general” than most chemical fungicides we have available, and are therefore able to fight multiple plant diseases that affect poinsettias under the right conditions (e.g. Fusarium, Botrytis, Rhizoctonia).  Their use may help mediate potential calamities from misdiagnosis and incorrect fungicide selection.

 

 

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This entry was posted in biopesticides, diseases, Fungal diseases, Fungicides, Poinsettia, Pythium, Thielaviopsis and tagged , , , , , . Bookmark the permalink.

One Response to Fainting “Freedom Red”? Wilting “Whitestar”? Potential causes of Poinsettia collapse, solutions, and the importance of testing.

  1. I am happy that I found your post while searching for informative posts. It is really informative and quality of the content is extraordinary .

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