Controlling whiteflies on poinsettias has been challenging since sweetpotato whitefly, Bemisa tabaci, first appeared in Florida in 1986 and then began to appear in greenhouses soon after. It was found to be a new, more insecticide-resistant strain, termed ‘B-biotype,’ with a broader host range than the usual B. tabaci. In 2004 an even more resistant strain, the Q biotype, was found in the US on poinsettia. Initially, these two biotypes were thought to all belong to the same B. tabaci whitefly species but researchers now think they comprise a complex of 20 different species that you can’t distinguish by appearance alone although they may even be found together in the same greenhouse. Recently, Canadian researchers found in greenhouses using biological controls that the more susceptible B biotype is capable to displacing Q in greenhouses using biological controls, which is good news for those of you using natural enemies for whitefly management.
The Q biotype has developed resistance to a number of commonly used pesticides including pyriproxyfen (Distance), buprofezin (Talus), pyridaben (Sanmite), and abamectin (Avid) with reduced susceptibility to the group 4A neonicotinoid insecticides; (imidacloprid (Marathon and many generic products), acetamiprid (TriStar) and thiamethoxam (Flagship). It appears to still be susceptible to dinotefuran (Safari), another neonicotinoid, however.
This season, some growers have applied Kontos (spirotetramat), early as a soil drench with good results. (It’s too late now). Although systemic, Kontos is very water insoluble and slow acting so it is best used preventively. As a rule insecticide drenches tend to be long-lasting (4 to 6 weeks) and Kontos is most effective against immature stages of whiteflies.
Some growers have also applied the new insecticide, Rycar (pyrifluquinazon) with good results. In recent trials as a foliar spray, it has provided excellent control of Bemisia B biotype as long as there was good coverage. In trials there was no phytotoxicity to poinsettias using sprays. It works on contact and also has translaminar activity.
XXpire WG, a new product, is a mixture of spinetoram and sulfoxaflor. While spinetoram is similar in many ways to Conserve in what it controls, sulfoxaflor, represents a completely new mode of action for greenhouse growers. Although it is a ‘Group 4’ material like the neonicotinoids and controls many of the same pests, it is not a neonicotinoid and is only labeled for use as a foliar spray. According to Rutgers IR-4 WF efficacy data, it exhibited excellent control of Bemisia (B biotype) especially eggs and immatures.
Mainspring (cyantraniliprole) is labeled for both foliar and systemic use. In research trials, it has provided excellent control for Bemisia whiteflies (B biotype) but less so for greenhouse whiteflies. However, Mainspring is best applied early so the whiteflies don’t establish on the poinsettias and efficacy against whiteflies on poinsettia may be improved by addition of a wetting agent (like CapSil). Spray residues on bracts are noticeable so growers would be advised to conduct their own small-scale trials. Drenches in containers will be long lasting. Mainspring is also compatible with at least some biocontrols (Amblyseius swirskii and Eretmocerus).
Judo (spiromesifen) provides excellent control of Bemisia Q and B biotypes and has performed consistently well against established populations. It is labeled as a foliar spray and has translaminar activity and also controls various kinds of mites, but as with other materials where foliage is dense, good coverage will improve results. We are not aware of any reports of injury to bracts from applications of Judo.
Safari applied as a soil drench or foliar spray has been very effective against either biotype. Expect 4- 6 weeks residual with drench applications and Safari is suggested where end-of-season treatments are needed. Wholesale growers should consider treatment soon. According to IR-4 data, it has been among the best performing products. Safari is highly water soluble and taken up into the foliage as plants grow. Drenches will not be effective on plants with unhealthy roots. Some growers have found removing lower leaves that are heavily infested will help reduce infestations and help improve coverage when sprays are applied. (Do not confuse empty pupal cases with other immature stages.) Old lower leaves that curl under can harbor large infestations of whiteflies. As bracts turn color, poinsettias become more sensitive to spray injury. In addition to Safari, in past years some growers have used, pyridaben (Sanmite), and acetamiprid (TriStar) as foliar sprays in bract stage without causing any noticeable damage on poinsettia varieties such as ‘Freedom’, ‘Prestige’ and ‘Monet’.
Pesticide applications to poinsettia bracts are risky for several reasons. Differences in cultivars, culture and environmental conditions may increase or decrease bract sensitivity to pesticides and unlike lower leaves, which can be removed, bracts need to remain and appear ‘perfect’ at sale. If you are inexperienced with using a particular pesticide, always test a small portion across varieties before treating your entire crop. Be sure to follow label directions exactly. See the company's website to read any technical bulletins about the product or call the company's technical representative before using a product for the first time.
After the poinsettia season is over, be sure to thoroughly clean your greenhouse: remove all poinsettias and weeds so the whiteflies do not have host plants to feed on. Careful attention to proper sanitation is needed to prevent whiteflies from becoming established on spring plants.
If you plan to grow poinsettias next year, consider using biological controls against whiteflies.
Resources
Are All Whiteflies the Same? By Andrew Frewin and Graeme Murphy (Grower Talks)
Whitefly Efficacy Summary 2014 – Rutgers IR-4 Program
Whitefly Trouble in Poinsettia Production by Ron Valentin, Biobest (Greenhouse Product News)
Additional Studies from the North American Poinsettia Trials, Jim Barrett, University of Florida and John Dole, North Carolina State University (Greenhouse Product News)
Originally posted Oct 8, 2014 by
Leanne Pundt, UConn Extension, Dan Gilrein, Cornell Univ., LI Horticultural Research & Extension Center, Tina Smith, UMass Extension
Updated Oct. 15, 2015
