Fourth International Bemisia Workshop International Whitefly Genomics Workshop
Biological Control of Whitefly in Poinsettia in Ontario, Canada
1 Ontario Ministry of Agriculture, Food and Rural Affairs, Vineland, Ontario, Canada. Correspondence: graeme.murphy@omafra.gov.on.ca
2 Eco Habitat Agri Services, Puslinch, Ontario, Canada
3 Plant Products Co. Ltd. Brampton, Ontario, Canada
4 Global Horticultural Inc. Beamsville, Ontario, Canada
5 Koppert Canada Limited, Scarborough, Ontario, Canada
This presentation describes the results of biological control trials in 13 commercial poinsettia crops in 2006 in Ontario, comparing treated and untreated crops, the use of eggplants as trap plants/banker plants and their impact on the efficacy of biological control. These trials were a cooperative venture among government extension services and industry representatives (including major biocontrol producers, biocontrol distributors and private consultants). In preliminary trials in 2005, whitefly biological control programs were established in 3 commercial poinsettia crops in Ontario, Canada. Trap plants (tomato and eggplant) were used to investigate whether these had potential as either monitoring tools or as banker plants to enhance the regular introductions of insectary-reared insects. Parasitoid wasps, (Eretmocerus mundus and Encarsia formosa) were released to control Bemisia tabaci (= B. argentifolii) and Trialeurodes vaporariorum respectively. Two rates of introduction were used. A high rate of Er. mundus was released in two of the three greenhouses, at a total of approx. 20/m2 (approx. 2/ft2) over the life of the crop. In the same two greenhouses, En. formosa was released at a total of 10/m2 (approx.1/ft2) over the life of the crop. A lower rate of introduction was used in the third greenhouse, with Er. mundus and En. formosa being released at about one third of the rate described above. At one of the two greenhouses using the high rate of introduction, good control was achieved with no insecticides being applied and only 2% of plants at shipping showing any evidence of whiteflies. In the other two greenhouses, whitefly populations started to build up towards the end of the crop and by mid-October, growers at both facilities began a clean-up spray program using pyridaben. Insufficient introduction rates of parasitoids were considered to be a contributing factor to the whitefly increase in one of these greenhouses, and in the other, there was evidence of pesticide residues as a limiting factor in success. The trap plant trial demonstrated considerable potential as a monitoring tool. Eggplant was significantly more attractive than both poinsettia and tomato to both species of whitefly. Tomato was more attractive to T. vaporariorum than poinsettia, but not as attractive to B. tabaci. As a banker plant, the trial was less successful, with limited reproduction and colonization of the parasitoids, especially Er. mundus. This may have been due to the fact that commercial cultivars of tomato and eggplant were used, which led to management problems in controlling height and vigour. Growers approached this by using strategies such as pinching and excessive use of growth regulators, both of which could have reduced whitefly populations and consequently parasitism. The other issue to note with the use of eggplant is that it is also very effective as a trap plant for thrips, aphids and mites. To respond to these concerns, predatory mites (Amblyseius cucumeris) were released preventatively on the trap plants and biocontrol agents for aphids and mites were used as necessary. In 2006, the program was expanded to include a major Ontario propagator of poinsettia cuttings. Er. mundus and En. formosa were introduced from February to July at a total rate of 15/m2 (approx.1.5 /ft2) and 7.5/m2 (approx.0.75/ft2) respectively. Until the beginning of June, less than 2% of stock plants were found infested with whiteflies. However, during the month of June this increased to 10%, due in large part to an influx of whiteflies from an adjacent area of the greenhouse where overwintering houseplants had been housed. While not a large infestation, low numbers of whiteflies were found on a large number of plants in a localized area, skewing the final count of infested plants. Encouraging levels of parasitism of B. tabaci and T. vaporariorum by Er. mundus and En formosa respectively were evident. Additionally, 13 growers of finished poinsettias agreed to use biological control on their whitefly in the 2006 season (from August-November). Treated crops ranged in size from 1100 m2 (12,000 ft2) to 13,500 m2 (150,000 ft2) with a mean of 4100 m2 (46,000 ft2). A program of introductions was developed based on that used by the successful grower the previous year, with a safety factor of 50% higher introductions built in. Thus, the growers in 2006 worked with total introduction rates of 30 Er. mundus and 15 En. formosa per m2 (approx. 3 and 1.5 per ft2 respectively). It was calculated that this would result in a final cost to growers of less than $0.10/pot (based on a 15cm pot), a cost that is competitive with the use of pesticides. Introductions were weighted towards the beginning of the crop with proposed introductions of Er. mundus at 3/m2/week (approx. 0.3/ft2/week) for 6 weeks, followed by 2/m2/week (approx. 0.2/ft2/week) for a further 6 weeks. Not all growers committed their whole crop to biological control, which allowed comparisons between treated and untreated areas. Eggplants (using a dwarf variety, Stokes Seeds, cv Baby Bell) at a rate of 1/100 m2 (approx 1/1000 ft2) were used by some of the growers as trap plants/banker plants. In some cases, the whole crop was interplanted with eggplants, and in others, some areas were left untreated, again allowing for comparisons. Results from these trials are presented and discussed in relation to the potential for biological control in commercial poinsettia crops.
|
PREVIOUS Effects of SB Plant Invigorator® on Bemisia tabaci Development in Tomato Plants |
NEXT Establishment and Impact of Exotic Aphelinid Parasitoids in Arizona: A Life Table Approach |