|The DNA analyzer at BCMAL was used to obtain genetic sequence information from Bemisia samples.
Photo courtesy BCMAL
In the final analysis, the season was by no means disastrous in terms of whitefly, but growers did have to give some thought to their control and it was relatively easy to find whiteflies in November. At about this time in both British Columbia and Ontario, we decided to sample whiteflies from greenhouse crops and test them for biotype. The Plant Diagnostic Lab of the B.C. Ministry of Agriculture and Lands had recently gained access to a new molecular (DNA) diagnostic test from an ARS-USDA lab.
Whiteflies were collected from 10 greenhouses in Ontario and sent to B.C. for testing. Molecular analysis revealed the presence of Q biotype in eight of the 10 greenhouses sampled. In B.C., whiteflies were collected from two poinsettia greenhouses and both were positive for Q biotype. The findings are not surprising. Indeed it would have been unusual had we not found Q. There were already reports from the U.S. that Q biotype had been found in poinsettia in a number of states earlier in the season, and since Canada gets its cuttings from the same sources as most U.S. growers, the results were expected.
|Tracy Hueppelsheuser (left) and Lisa Wegener in the BCMAL diagnostic lab.
Photo courtesy BCMAL
conducted in the U.S. a few years ago indicated that Q biotype is resistant to the neonicotinoids (Intercept, Tristar), and the insect growth regulator Distance (which was only registered in Canada in early 2007) and Talus (which is not registered in Canada).
So what products does that leave us with? Dyno-Mite, based on the experiences of Ontario growers, still works well. Forbid (which was registered in mid-2007) is apparently still effective and is recommended in the U.S. for control of Q. A few growers used it in Ontario in 2007 and it appeared to work quite well. Other registered products such as Enstar II may still be useful although there isn’t much data available to confirm this. The concern with Q is that it will develop resistance to these newer pesticides, especially if too much reliance is placed on them. For products not yet registered in Canada, resistance may develop in propagating countries before we ever get a chance to use them.
The other option open to growers is biological control, which is equally effective against B and Q biotypes. Trials in commercial greenhouses in Ontario in the last few years have demonstrated that biocontrol can be very effective using the parasitoid, Eretmocerus mundus. Other parasitoids such as Encarsia Formosa and Eretmocerus eremicus can also be useful in controlling greenhouse whitefly if present in the crop. In 2006, nine out of 12 greenhouses using biocontrol grew the crop successfully without insecticides. In 2007, the success rate was eight out of 11. In greenhouses where the cuttings came in with few or no whiteflies, the success rate was even higher.
|Graeme Murphy, OMAFRA|
Graeme Murphy is the greenhouse floriculture IPM specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs at Vineland.
Tracy Hueppelsheuser is an entomologist with the British Columbia Ministry of Agriculture and Lands. Lisa Wegener is a research pathology assistant with the British Columbia Ministry of Agriculture and Lands.