Preventing poinsettia problems

Photos: Jim Barrett

When poinsettia season comes, that also means the arrival of pests and diseases that affect the popular holiday crop. In the realm of insects and diseases, two of the most common poinsettia problems for growers are whitefly and Botrytis.

Whitefly

The two most common whitefly species in the greenhouse are the sweetpotato or silverleaf whitefly (Bemisia tabaci), and the greenhouse whitefly (Trialeurodes vaporariorum), says Dr. Lance Osborne, professor of entomology at the University of Florida. However, there are two unique types of B. tabaci (B- and Q-biotype) that need to be managed differently.

The B. tabaci B-biotype whitefly uses its piercing-sucking mouthpart to remove fluids from the plant and turn it white, Osborne says. Adults and immatures produce honeydew, which makes the plant sticky if it is not humid in the greenhouse. If it is humid, sooty mold can grow on the honeydew. Another issue with B-biotype whitefly is that customers simply do not want to see it on their plants.

The B. tabaci Q-biotype whitefly does not turn plants white like the B-biotype does, but it does have a high resistance to pesticides, Osborne says. “The difference between B- and Q-biotypes really is, Q is much more difficult to control because of its tolerance to pesticides,” he says. “If we screw up and make a resistant B, then I’d say that the B would probably be more important than the Q.”

The greenhouse whitefly was one of the major pests on poinsettia before the B-biotype of B. tabaci arrived in the 1980s and Q-biotype in the 2000s, Osborne says. “It doesn’t cause quite the same issues as the Bemisia does, but it can feed on [the plant], debilitate it, produce honeydew and sooty mold, and people don’t want to see it,” he says.

Osborne says he has evaluated the effect of Rycar®, a SePRO product with the active ingredient pyrifluquinazon, for managing the Q-biotype, and he was impressed. “It’s one of the few tools that we recommend for Q-biotype that wouldn’t be a neonicotinoid,” he says. “Because of issues with pollinators and neonics, we have done quite a bit of research and found that we have a small list of non-neonics that actually manage the Q-biotype.”

That’s a benefit that hasn’t been lost on Evan Jones, head grower at Spring Creek Growers Nursery in Waller, Texas. Jones uses Rycar in a rotation with other chemistries, including SePRO's insect growth regulator Talus®. Although he does use a neonicotinoid drench in managing whitefly, Jones says he likes Rycar because it’s good on bee health and is specialized. “You just really want to go after one target, and with poinsettias, it’s primarily whiteflies,” he says.

While Osborne saw results with Rycar on the Q-biotype, Jones battles with the B-biotype. “I haven’t seen the Q-biotype yet,” Jones says. “It’s really hard to determine if you have it or not. I don’t think we’ve seen it. But it’s always a concern, because it’s much more difficult to control than the [B-biotype].”

Three years ago, Metrolina Greenhouses’ research and development department worked with SePRO to test Rycar for whitefly, and it has since implemented it into its IPM program for poinsettia production, says director of growing Ivan Tchakarov, who calls Rycar a “golden tool” for the business.

Additionally, Metrolina Greenhouses uses cultural practices to combat whitefly, including regular scouting and managing screens and vents, Tchakarov says.

Overall, the industry has done well in managing whitefly, Osborne says. “If you’re bringing in poinsettia, you stand the risk of getting any one of the three types of whitefly,” he says. “Growers need to really inspect their material — they need to probably isolate it somewhere before they put it into their greenhouses.”

Botrytis

Another culprit for problems on poinsettia is the fungal disease Botrytis, explains Mark Brotherton, portfolio leader at SePRO. This disease thrives on dense-canopied plants such as poinsettias that hold a significant amount of moisture.

Growers can reduce the potential of Botrytis by following a few crucial steps, Brotherton says. “Culturally, ways to provide an unfavorable environment for Botrytis development are to have properly spaced plants, good ventilation, low humidity, avoid excess watering — and that includes avoiding watering late in the day or at night,” he says. “Water does not evaporate at the same rate during those parts of the day.”

From a chemical perspective, the SePRO fungicide Decree®, with the active ingredient fenhexamid, has been a standard for Botrytis control, Brotherton says. “It provides preventative and curative control, and the appealing part, especially on poinsettias, is that there are no crop safety concerns,” he says. “Decree also leaves no residue, which is very important throughout the crop but especially when the bracts break color and are ready to sell. Customers do not want spots on the bracts.”

Decree offers an effective late application because of the little amount of residue that it leaves, Brotherton says. It is the only ornamental fungicide in Fungicide Resistance Action Committee (FRAC) Group 17, and it should be used as part of a rotation with other fungicides to limit the potential of building resistance.

Tchakarov says he uses Decree as part of a weekly rotation.

Growers should start their programs before the onset of conditions that are favorable to Botrytis, such as cool weather and the development of dense foliage, Brotherton says. “It’s a lot easier to prevent diseases then it is to curatively get rid of them.”

In a variety of circumstances, growers can avoid whitefly and Botrytis issues on their poinsettia crops by consulting with other growers, researchers and technical experts; performing proper cultural practices; and using tried-and-true products from trusted companies. — Patrick Williams

*Always read and follow label directions. Rycar and Talus are registered trademarks of Nichino America, Inc. Decree is a registered trademark of Arysta LifeScience North America, LLC.