Two alternative strategies for looper management in greenhouse vegetables
Project Code: PRR06-930
Renee Prasad - E.S. Cropconsult Limited
To evaluate the efficacy of two biopesticides, Bacillus Thuringiensis (Bta) and Trichogramma sibericum, for loopers in greenhouse pepper, tomato and cucumber
Summary of Results
Cabbage looper (Trichoplusia ni) is a priority pest for greenhouse vegetable production. One reason for the priority status is that the integrated pest management (IPM) tool box for this pest is limited. Further, the performance of non-chemical tools for looper control is perceived to be inconsistent. As a consequence, some pepper growers have started to rely heavily on chemical insecticides for management.
Products based on the microbial agent Bacillus thuringiensis kurstaki (Btk) are available and used regularly in vegetable greenhouses. However, there are concerns regarding Btk -resistance development. Bacillus thuringiensis aizawai (Bta), which is a different Bt subspecies, has been used successfully to manage lepidopteran pests of field crops in the southern US, where alternating Btk with Bta has become standard practice for some growers (Rowell and Bessin 2005). Such a program could be an effective model for the greenhouse industry in Canada.
Adding another species of Trichogramma wasp (T. sibericum) may also enhance looper management by improving biological control. Currently, Trichogramma brassicae is the only commercially available egg parasitoid for loopers and its use is not widespread, in part because of the difficulty in demonstrating efficacy. In preliminary work (ES Cropconsult, unpublished) different Trichogramma species were observed to search in different areas of the crop canopy. These preliminary results suggest that a combination of Trichogramma species, rather than just one, may be the key to more effective looper egg parasitism.
The objective of this study was to investigate two additional tools - Bta and Trichogramma sibericum - that could be used to delay or reduce the number of insecticide applications applied to the vegetable greenhouse crops.
Bta trials were conducted with the product XenTari (Valent Biosciences, Libertyville, IL) which is commercially available in the US and used for Lepidopteran control in a variety of crops. Trials were conducted in a small research greenhouse and separate trials were conducted for tomato, cucumber and peppers. Plants were infested with looper larvae prior to being sprayed. Results on tomatoes and peppers indicated that XenTari was effective at reducing the number of live looper larvae, within 48-h of spraying. On cucumber, no effect was observed of XenTari on survival of looper larvae mainly because of the conditions of the trial.
Trials with T. sibericum were conducted in commercial pepper greenhouses. The study consisted of three treatments: T. brassicae alone, T. sibericum alone and T. brassicae and T. sibericum together. The main measure of efficacy for this trial was parasitism of sentinel Ephestia kuniella egg cards, which were located at varying distances from Trichogramma release points. Dispersal through the crop is a major factor limiting the success of Trichogramma wasps in controlling pests. By placing these egg cards at different distances from release points, the dispersal of wasps through the canopy could be measured. Overall, there were no differences among the three treatments in terms of dispersal through the canopy. Indeed the results indicated that dispersal through the canopy, for both species, is very limited with wasps generally moving vertically rather than laterally through the pepper canopy.
In summary, the results support the addition of Bta-based products like XenTari to the looper IPM tool box, with the caveat that operational issues such as the volume of water required to achieve proper coverage in commercial greenhouses and potential cross-resistance of Bta and Btk be addressed with further study. The results do not support further study with T. sibericum as it did not perform better than the commercially available T. brassicae. However, the results suggest that the efficacy of T. brassicae may be improved if the number of release points/unit area were increased.
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