Poinsettia Biocontrol Update

July 16, 2013

Start with plants free from pesticide residues
Wholesale stock plants, cutting producers and rooting stations of poinsettias are encouraged to use IPM practices and pesticides that are compatible with biological control agents (BCA) or use BCAs during propagation.  To find out if a pesticide is compatible, use one of the on-line searchable side effect data bases available from suppliers. Click on "Side Effects" Enter product and natural enemy to search. Biobest Koppert

Note: Last year, Koppert, Canada collected leaf samples of cuttings that arrived at a few rooting stations in Canada. The samples were then sent to a pesticide residue laboratory in Holland. Test results revealed that 26 insecticides and 20 fungicide residues were detected on the cuttings. See the article recently published in GPN magazine: Whitefly Trouble in Poinsettia Production

When purchasing cuttings, know the pesticide and pest history of your cuttings to prevent failures using biocontrol due to pesticide residue.

Start clean, finish clean
Experience based upon case studies have shown that growers that have initial whitefly populations on less than 5-7% of their plants (total for all stages of development) are more likely to finish the crop with less than 20% infested plants, whether they use biological or chemical controls. Growers that start with higher than 5-7% of their plants with whitefly are likely to finish the crop with greater than 20% of infested plants. If growers have more than 20% infested plants, they may need pesticide cleanup treatments before shipment.

Ontario Case Study - Canadian growers and whitefly control:
In this study Canadian growers dipped rooted and unrooted poinsettia cuttings using Botanigard WP (not ES formulation) plus Rootshield to reduce whitefly infestations upon arrival to begin their biocontrol program with cleaner plants. The ES formulation of Botanigard is phytotoxic to poinsettias. Both pesticides are labeled for use for dipping (in US) and are safe to use with parasitic wasps for whitefly. The process of dipping plants has been very controversial due to the risk of spreading disease, and is not advised by plant pathologists. Growers try to minimize the risk for spreading disease when dipping by mixing separate solutions and dipping separate batches from different suppliers and never using left-over dip solution for treating plants.

To monitor for whiteflies, growers used whole plant observation, not just sticky cards. They inspected the undersides of leaves for the presence of late instar immature whiteflies or adults. Whole plant monitoring determines the % of plants on which live whitefly are found. If even a single whitefly is found on a plant, it is recorded as an infested plant.

In these case studies, the time taken for whole plant monitoring was similar to that needed to change and count sticky cards, especially in the first few weeks when the plants were smaller. However, sticky cards can be useful for detecting localized infestations, or help to detect where a population of whiteflies originate.

At least 100 plants per acre (more in smaller greenhouses) with a minimum of 10 plants per bay were inspected. Each variety of poinsettias variety was monitored.  Growers may want to monitor more plants for those varieties or shipments that are more prone to whiteflies, based upon their past experience.

Release Rates
In the Ontario project, the primary BCA for control of Bemisia tabaci (Sweet potato whitefly, including the Q biotype) was Eretmocerus mundus, or Eretmocerus eremicus at @ 0.3/ft 2/week for 12 weeks. After 6 weeks the program was assessed to decide whether further introductions were needed for the next 6 weeks. For Greenhouse whitefly, Encarsia formosa was introduced at half the rates of E. mundus and for the same duration.

New England note: Instead of identifying  whitefly species, some growers have been using a combination of the two parasitoids with mixed results. The immature stages are used to identify the species of whiteflies to be able to choose the most effective parasitic wasp.  It is best to identify the species and choose the most effective biocontrol agent for that species.

Thresholds at time of shipping
The monitoring program was generally finished in the first week of November. At that time, any crop with less than 20% infested plants did not receive pesticide treatments. In most cases, an infested plant might have only 1 to 2 adult whiteflies on a fully grown plant.  If growers found more than 40% infested plants, clean up treatments were applied before shipping. There was a grey area between these two levels, but from observation, most crops with between 20-30% infestation, were unlikely to need additional whitefly controls just before shipping.

See article: Refining Poinsettia Production (GPN magazine -Scroll down to pg 15) Biocontrol of Silver Leaf Whitefly for 2012 Research - Timing of Introductions, Rate of Introduction and Costs

Photos: Empty vs parasitized pupae, Parasitized sweet potato whitefly, Encarsia formosa adult, Eretmocerus eremicus adult

Tina Smith, UMass Extension, Leanne Pundt, UConn Extension with input from Sebastien Jacob and Ron Valentin, Biobest and Graeme Murphy, IPM Specialist, Ontario