Which Pesticides are Effective for Whitefly?

Efficacy trials are key to keeping growers informed about which chemicals currently work and which don’t for Bemisia whitefly. 

Entomologists at the University of Maryland and Delaware recently did such a study, and included newer pesticide registrations. If you missed the article in the July issue of Grower Talks magazine, keep reading for the link to their results and a Canadian take on the study.

Done on poinsettia with the less-resistant (but still challenging) Bemisia “B” type (aka the Middle East-Asia species), Dr. Stanton Gill and his team tested a plethora of chemicals.

These were applied according to company-recommended rates and application dates.

Below is a summary of their final sampling date in October to get a sense of  how their treatments panned out at the end of the season. Most chemicals were applied in late August.  You can see their full methods and results here.

*At high curative rates.  When lower rates were applied preventively, there was very little suppression compared to the control treatment (water).

Here, “excellent” control refers to the pesticides that achieved only 1 or 2 adults/2 leaves on average and fewer than 20 nymphs/2 leaves.  Although this may seem high, keep in mind this was done in a research greenhouse with plants artificially infested with whitefly.

Generally, their results support what we are seeing in Canada in terms of  Bemisia chemical control in poinsettia with available products in “regular” (i.e. low pressure) years.  The additional registration of Ventigra in time for the 2019 poinsettia crop could be a promising alternative if your biocontrol program gets off track in early or mid-September (see this article on the “tipping point” when it comes to Bemisia biocontrol).  However, as a foliar, contact insecticide, good coverage of the crop with Ventigra will be key.