Whitefly management on poinsettia for fall 2013
Strategies to control whiteflies on poinsettia that have developed resistance to some insecticides include using clean cuttings, scouting and insecticides or biocontrol strategies.
Some growers had difficulty keeping whiteflies under control on their poinsettia crop last fall. This is most likely because of high levels of resistance to pyrethroid and nicotinoid insecticides, including some products that we have used extensively in previous years like imidacloprid. Here are some tips from Michigan State University Extension to help manage whiteflies in fall 2013.
Start with clean cuttings
Dip your cuttings in a solution of Botanigard, a fungal pathogen of whiteflies, and buprofezin, an insect growth regulator, just before planting. Both are safe to handle and are not harmful to poinsettia plants. This will help reduce the number of whitefly larvae coming in on your cuttings, and will give you a cleaner start.
Monitor whiteflies with yellow sticky cards. Change cards once per week and record the number of whiteflies found on each card. Use at least one card per house or one per 2,000 square feet.
Insecticide products most likely to work on resistant whiteflies
Several nicotinoid insecticides are labeled as a soil drench for whitefly control. Whitefly resistance to imidacloprid is widespread, and unfortunately, resistance to other nicotinoid insecticides is also becoming common. Among the systemic products available to use as a soil drench, whiteflies are least likely to be resistant to Safari, although Q biotype whiteflies may be resistant to Safari.
We have more choices when considering what to use for foliar sprays. Consider using three of the following products, spraying once per week when unacceptable numbers of whiteflies are found on sticky cards, by rotating to a new product each week. That way, if one does not work well, the other two may carry you through the fall.
- Orthene 97
Another strategy that has shown to be effective by research conducted by Raymond Cloyd at Kansas State University is to rotate materials like Distance, Endevor and No-Fly (this product requires relative humidity above 70 to 75 percent to be effective) as foliar sprays on the cuttings, and then apply the Safari after potting as soil drenches. Wait as long as possible to apply the Safari so it holds through bract coloration.
What about biological control?
You may have seen an article in the July issue of Greenhouse Grower Magazine about using biological control for whiteflies on poinsettia. More growers are experimenting with biological control and some have been successful. In the article, it recommends that growers begin releasing two parasitic wasps species, Encarsia formosa and Eretmocerus mundus, immediately after sticking cuttings. Unfortunately, the cost of releasing both wasps at the recommended rate may be three or four times the cost of spraying once per week. Also, if the cuttings have insecticide residue on them, which is likely, they may be toxic to the parasites.
For growers in Michigan, 95 percent of our whiteflies on poinsettia are Bemisia tabaci – sweet potato whitefly or silverleaf whitefly. Only Eretmocerus mundus will work on Bemesia tabaci, so for poinsettias, you may only want to release E. mundus and not E. Formosa, which only works on greenhouse whitefly.
If you decide to use biological control, I suggest starting slowly, maybe with one house, until you feel more confident. Very few growers in Michigan have relied on biological control of whiteflies on poinsettia in the past, but more are experimenting and this could change in the future.
Note: More information is available on the Wall Chart, “Insect Controls for the Greenhouse Industry,” MSU Extension Bulletin E-2696.
Dr. Smitley's work is funded in part by MSU's AgBioResearch.