Q-Biotype Whitefly Update

September 2, 2005 - 11:34

The following information about the most recent Q-Biotype whitefly came from a letter sent to propagators by Craig Regelbrugge, senior director of government relations for the American Nursery and Landscape Association (ANLA) and Lin Schmale, senior director of government relations for The Society of American Florists (SAF).

As we are all aware, growers in the United States have been battling the B biotype of the silverleaf whitefly (Bemisia tabaci) since its introduction in the late 1980s. This biotype caused significant losses for several years, but has been more manageable since the mid 1990s when several new insecticide classes were introduced. However, earlier this year, discovery of the Q biotype silverleaf whitefly was reported from Arizona and, subsequently, from other states as well. The Q biotype could pose a significant threat to the ornamentals industry, as well as the U.S. cotton and vegetable industries because it is less susceptible to many of the insecticides that growers currently rely on to manage the B biotype.

Although the Q biotype has been established in the Mediterranean basin and central Europe for many years, this biotype had not been previously reported in the United States. A national, USDA-coordinated survey is currently underway to estimate how widely this pest is distributed. However, it is very important at this time for growers to be especially observant of whiteflies in their greenhouse crops and ask for expert advice if they are having trouble controlling them.

Currently, it is uncertain whether the level of resistance observed in the laboratory studies to date is great enough to cause an obvious reduction in field performance when insecticides are applied according to the label. Greenhouse trials are currently underway at the University of California to help answer this question, and to determine which insecticides are most effective against the Q biotype. Results from these trials will be posted at: http://www.mrec.ifas.ufl.edu/LSO/bemisia/bemisia.htm. Other information on whitefly management is also available at that Web site.

Whiteflies have a very wide host range and can potentially impact many ornamentals crops, as well as cotton and vegetable crops. However, because poinsettia is one of the host species and the industry is entering the poinsettia season, now is an important time for growers to pay particular attention to whiteflies on their poinsettia crops.

Greenhouse trials will not be complete until after many growers have initiated whitefly management programs. Therefore, at the request of SAF and ANLA, university and industry experts have developed a “Best Guess” pesticide program for the Q whitefly on poinsettia. To get a copy of this program visit the Web site above. Please be aware that this program may change based on the outcome of greenhouse efficacy trials and may not apply to all populations of Q biotype whiteflies.

It is important for growers to place currently available information about the Q biotype into context. On the one hand, there is no reason to panic. Decreased susceptibility does not mean an insecticide will completely fail to control the Q biotype. Producers of floral and nursery crops have been managing the Q biotype in Europe for many years — and are still in business. In addition, a couple of newer insecticides have recently been registered that have been quite effective against the Q biotype in Europe.

A whitefly control problem does not necessarily mean a grower even has the Q biotype. A lack of control is most often due to factors other than insecticide resistance (ex. poor spray coverage), or you may have a population of the B biotype that is developing resistance. And go back to the basics; scouting is essential to the success of any pest management program (see below for additional comments on scouting). Good sanitation is key. Get rid of weeds, old “pet plants” and anything else that might serve as a refuge for the insects you’re trying to get rid of. And remember the importance of rotating chemicals for different classes of action.

On the other hand, growers should also not be complacent about the Q biotype and assume that their current management program will be effective, especially if they are relying on just one or two products. It is likely that ongoing greenhouse trials will demonstrate that certain insecticides are less effective against the Q biotype than they are against at least some populations of the B biotype, especially with respect to the length of residual control.

SAF and ANLA strongly recommend that growers who experience unexpected difficulty in controlling whiteflies should contact their local county adviser, extension agent, propagator’s advice team or submit a sample for biotyping. This step should be taken early in the crop cycle before whiteflies become established and spray coverage becomes an issue.

A list of laboratories that can biotype whiteflies is listed with the Best Guess information. Growers should contact one of these labs prior to shipment of samples, to make sure correct sampling and shipping procedures are followed. The results will be proprietary to your business and will remain confidential, if you so request.

If you have questions or concerns, visit the Web site above, established by Lance Osborne, University of Florida. Or contact your local pest adviser or your propagator. More updates will continue as the season progresses.

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