Native to Central America, poinsettia (Euphorbia pulcherrima) has become one of the most beloved holiday plants in the United States. With dramatic red bracts and crisp dark green leaves, poinsettia cheers us as the days grow ever shorter. (Bracts are small, leaflike structures often positioned beneath a flower and can appear to be petals. They are different from the normal leaves of a plant.)
Americans can choose from among dozens of varieties to raise their holiday spirits. And we do. According to the U.S. Department of Agriculture (USDA) National Agricultural Statistical Service Census of Horticulture, retail sales of poinsettias reached more than $215 million in 2019.
The USDA’s National Institute of Food and Agriculture (NIFA) supports poinsettia production via the IR-4 Project. Established in 1963 by USDA, the IR-4 Project ensures that specialty crop farmers have legal access to safe and effective crop protection products. The IR-4 Project operates as a unique partnership between NIFA, USDA’s Agricultural Research Service, State Agricultural Experiment Stations, the U.S. Environmental Protection Agency, the agrochemical industry, commodity groups, and growers.
In recent years, additional partnerships have been formed with USDA’s Foreign Agricultural Service, which supports international specialty crop export activities; USDA’s Animal Plant Health Inspection Service to work on selected invasive species; and the U.S. Department of Defense’s Deployed Warfighter Protection Program to provide regulatory support for public health pesticides.
Breeding and Production
During the last 180 years, horticulturalists and breeders have developed new varieties with special characteristics. Beyond the traditional red, available bract color now includes white, cream, and pink solids, along with various speckles and patterns. Bract shape has also developed over time from a simple leaf shape to twists and ruffling. One of the most desirable traits discovered early last century – enhanced branching after pinching – is now known to be caused by a phytoplasma (an intracellular parasite).
Even with the breeding programs to develop new colors and forms, production practices are still rooted where poinsettias originated. Poinsettia plants require special production methods to encourage the bracts to change color in time for holiday cheer. Growers must provide shorter days by drawing black cloth over the plants to simulate a longer period of darkness. Even a small flash of light during the night can inhibit the transformation.
IR-4 Research
Poinsettias are prone to multiple bacterial and fungal diseases, including bacterial canker; bacterial stem rot; botrytis flower blight and stem canker; powdery mildew; Phytophthora root and stem rot; Pythium root rot; Rhizoctonia root rot; leaf scab; and Thielaviopsis root rot. There are multiple insects and mites that can cause damage to poinsettia, including fungus gnats, whiteflies, western flower thrips, broad mites, Lewis mites, aphids, mealybugs, and scales.
Of the various diseases and pests affecting poinsettia during production, IR-4 has worked to develop efficacy information on some key problems: Phytophthora root rots, Pythium root rots, bacterial diseases, Botrytis, Q and B biotype whiteflies, mealybugs, scale, and western flower thrips. In addition, IR-4 has conducted 40 crop safety trials to determine whether products may be applied to poinsettias without injury or without leaving unsightly residues.
With IR-4 data, the following products have been registered:
- Bacterial diseases*: Regalia, ZeroTol
- Botrytis*: Botector, Broadform, Mural, Orkestra, Regime, Spirato, Stargus
- Phytophthora & Pythium*: Heritage, Insignia, Rootshield Plus, Segway, Subdue Maxx
- Mealybugs and Scale: Aria, Altus, GrandEvo, Sarisa, Ventigra
- Thrips: Altus, Aria, Grandevo, Hachi-Hachi, Mainspring, Overture, Pedastal, Safari, Xxpire
- Whiteflies*: Aria, Grandevo, Pedestal, Rycar, Xxpire
Source: nifa.usda.gov