Finish strong

Some growers find sleep elusive during poinsettia season, especially as the bracts begin to change color. Concerns multiply as they reach the finishing stage, leading them to constantly question: “Have the right moisture, pH and EC levels been reached in the media? Is it time to spray calcium to aid bract development? Is the temperature too warm or too cool? What about the light level? Are the plants becoming too stretchy?” These questions add to existing worries about pests and diseases. However, growers can enjoy a good night's sleep knowing that there are answers and solutions available for these challenges.

Size management with plant growth regulators (PGRs) are critical to producing a desirable poinsettia crop. However, some aggressive varieties may get out of hand as soon as the PGR application stops at the end of growing stage. It’s a misconception that PGRs cannot be used in the finishing stage. Topflor (fluprimidol) from SePRO is an effective and economical alternative to Bonzi (paclobutrazol) for growth control in the finishing stage.

A drench (or controlled volume drip irrigation) of Topflor at 0.5 to 1 ppm can hold the growth for finish height (Fig. 1). Topflor also toughens up the stems and helps the plants stand up to abuse during packing and shipping.

Several pests and diseases can cause problems in a poinsettia crop. Biological control agents (such as Eretmocerus wasp for whiteflies), biopesticides (such as SePRO’s Obtego for various root diseases), and cultural management practices (such as proper plant spacing and throwing out infected plants) help to produce a clean crop.

At the finishing stage, watch for whiteflies, fungus gnats, shore flies, stem and root rots by pythium and rhizoctonia, botrytis, and powdery mildew. Occasionally you may see spider mites, mealybugs, soft rot by erwinia, and other diseases such as phytophthora and fusarium.

Fungus gnats and shore flies can be problematic from propagation to finish. Maintaining the proper moisture and fertilization level to prevent prolific (even if they are not visible) algal or fungal growth in the media is critical to combating fungus gnats and shore flies. Adult fungus gnats and shore flies are not difficult to kill — pyrethroids and other contact insecticides can do this job well. But infestation will not be eliminated unless the larvae in the media are also reduced. Drench or sprench the media surface with azadirachtin (Ornazin; IRAC UN), cyromazine (17), dinotefuran (4A), or the nematode Steinernema feltiae. Be patient — it will take a couple of weeks before the larvae are eliminated and the adults disappear.

When given time and opportunity to build up a population, whiteflies can be devastating at the finishing stage. Growers have successfully managed whiteflies with drench and spray of neonicotinoids, such as dinotefuran and imidacloprid, for decades. Neonicotinoids are still effective, but growers who want alternatives to a neonicotinoid drench are turning to cyantraniliprole (28), flupyradifurone (4D), or spirotetramat (23). For quick knockdown of whiteflies, good options are spray of abamectin (6A), acetamiprid (4A), cyantraniliprole (28), dinotefuran (4A), flupyradifurone (4D), pyridaben (21A), pyrifluquinazon (SePRO’s Rycar; 9B), spirotetramat (23) and thiamethoxam (4D). Rycar, which is capable of causing adult whiteflies to fall off the plants within hours of application, is particularly effective for cleaning a crop of whiteflies before shipping.

We are seeing more Lewis mite and mealybug (mainly citrus mealybug and striped mealybug; Fig. 2) infestations in the finishing stage. Akari miticide (fenpyroximate; 21A) is an effective solution for all life stages of Lewis mite, as well as other mite species. Ornazin, Rycar, and Talus (buprofezin; 16) are solutions for mealybug infestations. To find more insecticides and miticides registered for the management of spider mites, mealybugs, and other pests, visit www.sepro.com/bugposter.

Disease outbreak is intimately connected to how poinsettias are being grown. Overfertilization can cause salt stress and damage to roots, which allow pythium and rhizoctonia to invade the roots and basal stems. Both diseases are also more severe in wet media. High humidity, due to poor ventilation or close plant spacing, benefits botrytis and powdery mildew. Infected plants should be treated or removed quickly to prevent spread. It’s important to remember that proper environmental and production management are the first steps in preventing disease outbreaks. We recommend proper pathogen identification (by a diagnostic service) so the right fungicides can be selected.

Stem and root rots are best managed through drench or chemigation (if allowed) of fungicides. Fungicides in FRAC Group 1 (thiophanate methyl), 3 (such as mefentrifluconazole), 7 + 11 (such as boscalid + pyraclostrobin), 11 (such as pyraclostrobin), 12 (fludioxonil), 14 (pentachloronitrobenzene or PCNB), and 19 (polyoxin D zinc salt) are effective options for fungal stem and root rots caused by fusarium, rhizoctonia, and black root rot. On the other hand, fungicides in FRAC Group 4 (mefenoxam), 7 + 11 (such as boscalid + pyraclostrobin), 11 (such as fenamidone), 14 (such as etridiazole), and 21 (cyazofamid) are good options for pythium.

Decree (fenhexamid; 17) and Pipron (piperalin; 5) are the industry standards for preventive and curative management of botrytis and powdery mildew, respectively. Research also suggests that applications of fungicides in FRAC 7 (isofetamid), 7 + 11 (such as azoxystrobin + benzovindiflupyr), and 12 (fludioxonil) are effective in managing botrytis infection. For powdery mildew, other effective fungicides include members of FRAC 3 (such as mycobutanil), 7 + 3 (pydiflumetofen + difenoconazole), 7 + 11 (such as fluxapyroxad + pyraclostrobin), 9 + 12 (cyprodinil + fludioxonil), and M1 (such as SePRO’s Camelot O; copper octanoate), as well as potassium bicarbonate. Camelot O, CuPRO 5000, and Junction (all contain copper; M1) are excellent choices for managing soft rot caused by erwinia. These copper fungicides should be rotated with fungicides from other FRAC groups (such as forsetyl-Al) to avoid resistance development.

An over-riding question in pest management during the finishing stage is, “Is the pesticide safe to bracts?” Bract safety varies among pesticides, pesticide formulations, poinsettia cultivars, application methods and rates, and environmental conditions. Sometimes, the burn on leaf edges may not be due to phytotoxicity but deficiency of calcium or environmental damage.

There is not one single location that lists bract safety information for all pesticides. Carefully review the information on a product-by-product basis because not every product with the same active ingredient or within the same FRAC or IRAC group has the same bract safety profile. For example, Rycar is safe but afidopyropen and pymetrozine are not safe to bracts although these insecticides are in IRAC Group 9. Also, emulsifiable concentrate and oil suspension have a greater likelihood of damaging bracts than other formulations, even if the active ingredient is the same.

Although many of the products mentioned do not explicitly prohibit application to poinsettia, we recommend a small-scale test for bract safety whenever you are using a product on a cultivar for the first time. Spray or drench six to ten plants with the product at the desirable application rate, then observe for any damage or discoloration on bracts three to seven days later.

Finishing a poinsettia crop can be challenging. However, with proper management, careful attention to moisture, pH, and EC levels, and effective use of products, it's possible to mitigate many common challenges. Vigilance in applying proven solutions and maintaining best practices will enable growers to produce a healthy and desirable crop, and find peace of mind during the demanding poinsettia season.

Juang Horng (J.C.) Chong, PhD is the SePRO Technical Development Manager - Ornamental.