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Unfortunately, poinsettia and sweet potato whitefly (Bemisia tabaci) go together like cats and fleas; if you have one, you’ll have the other. By this time (June) you should already be considering your whitefly management strategy. Here, we make a case for biocontrol as both a viable and economical way to control whitefly based on leading research supported by the American Floral Endowment (AFE) and many years of grower experience in Canada.

The Problem with Pesticides

Management of Bemisia whiteflies with pesticides can be difficult, if not impossible, in some years. This is because whiteflies that originate on cuttings (and those that fly in from field crops, as in the Southern US) have likely been exposed to multiple applications of several groups of pesticides before they even enter the greenhouse.

Overexposure to pesticides is a sure path to the development of resistance in whiteflies, especially in the whitefly species referred to as the “Q” type, which is common in poinsettia. For some good reading on B and Q type Bemisia (now officially called MEAM1 and MED, respectively) and the importance of rotating pesticides if you choose to manage whitefly chemically, see the article by J.C. Chong in the June 2018 edition of this newsletter.

However, pesticides aren’t the only option. An alternate management strategy we know works well in Canada for whitefly control is the use of preventative methods (i.e., cutting dips, outlined below) coupled with biocontrol. Compared head-to-head, this strategy has been shown to be just as effective as pesticides in years where there is little pesticide resistance in whitefly populations. 

In years where pesticide resistance is high, though, biocontrol is the only reliable method. Relying primarily on biocontrol to manage Bemisia in poinsettia has helped Canadian growers avoid anxiety and crop losses when chemicals start to fail.

Cutting dips

One of the main entry routes of whiteflies is on propagative material (cuttings). As we know, some years are worse than others, depending on the success of the whitefly control program at the propagator. The first step to a successful whitefly biocontrol program is reducing the number of whiteflies at the beginning of the crop. Otherwise, high whitefly numbers at the start of a production cycle may overwhelm the control capacity of biocontrol agents or significantly increase the cost of your biocontrol program as you add new natural enemies to control increasing numbers of whitefly “hot spots.”

Originally pioneered in Ontario, Canada, research has shown you can effectively reduce the numbers of whitefly at the start of your poinsettia program by dipping your unrooted cuttings in “soft” but effective insecticidal products upon receipt. These include insecticidal soaps, oils, and/or biopesticides. Not only does dipping provide full coverage, ensuring a high number of whitefly nymphs and pupae are killed, but the products used leave minimal residues and are compatible with biocontrol agents applied after the cuttings are stuck.

Research at the Vineland Research and Innovation Centre has shown that dipping unrooted poinsettia cuttings lowered Bemisia whitefly numbers on the cuttings by an impressive 70 percent. Best results were obtained against whiteflies using either of two dip recipes: 0.1% (v/v) SuffOil-X or a combination of 0.5% (v/v) Kopa insecticidal soap mixed with 1.25 g/L BotaniGard 22WP. Further greenhouse trials (Figure 1) demonstrated that dipping cuttings delayed whitefly population development on the plants, effectively setting back the clock by several weeks. This significantly improved the effectiveness of whitefly biocontrol programs thereafter, as it gave the biocontrol agents more time to start working.

The strategy of dipping cuttings to reduce incoming pest pressure in floriculture crops has now been adopted by 73 percent of commercial Canadian floriculture growers that grow from cuttings and is considered a critical tool when fighting difficult to control pets.

A few “Tips for Dips”:

  • Check product labels to ensure that dipping is included as an application method for your location.
  • Dip rates are lower than spray rates for soap and oil to prevent phytotoxicity. Test a small batch of cuttings before committing to a full dip program.
  • Total coverage of the foliage is required. Do not pack the cuttings too tightly and check for dry spots after the cuttings are dipped.

Figure 1. Average number of sweet potato whiteflies per poinsettia plant. In the dip treatment (solid yellow line), cuttings were dipped in insecticidal soap + BotaniGard 22WP. In the parasitoid treatment (blue line), parasitoids (Eretmocerus eremicus) were released weekly. The final and best treatment combined dips and parasitoids (dashed yellow line).

Choosing Biocontrol Options in Production:

After dipping, the next step in a successful biocontrol program is knowing which bios to use and when to use them. Unfortunately, there’s still no “one-size-fits-all” recipe for biocontrol of whitefly on poinsettia. However, many growers find success using one of the programs outlined below throughout production. One thing all three of these programs have in common is the use of multiple natural enemies to target multiple life stages of whitefly (Figure 2).

By Dr. Rose Buitenhuis, Senior Research Scientist Biological Control, Vineland Research and Innovation Centre, Vineland, ON, Canada, and Dr. Sarah Jandricic, Floriculture IPM Specialist, Ontario Ministry of Agriculture, Food and Rural Affairs, Vineland, ON, ,

Be sure to check out more of AFE’s research, watch Dr. Rose Buitenhuis’ recent webinar on Biological Control of Whitefly on Poinsettia, Dr. Sarah Jandricic’s session on Developing an Integrated Pest Control Program for Whitefly on Poinsettia and register for upcoming sessions