Management of onion thrips with biopesticides
Project code BPI09-020
Jeff Tolman & Heather Peill - Agriculture and Agri-Food Canada
This project is part of the North American Free Trade Agreement Biopesticides Initiative for demonstration and efficacy testing of biopesticides against onion thrips (Thrips tabaci) in Canada. A comparable project was undertaken through the IR4 program under the lead of Silvia Rondon (Oregon State University)
Summary of Results
This project was part of the North American Free Trade Agreement Biopesticides Initiative for demonstration and efficacy testing of biopesticides against onion thrips (OT; Thrips tabaci) in Canada. A comparable project was undertaken through the United States IR4 program under the lead of Silvia Rondon (Oregon State University).
OT are serious pests in onions and are widely distributed in Canada and the United States. They can cause significant economic damage by piercing the leaves and feeding on plant chlorophyll. Infested onion plants are also more susceptible to secondary infections.
OT have many natural enemies, which include ladybird beetles, minute pirate bugs, lacewings, spiders, and predacious and parasitic wasps. The fungus Entomopthora thripidum also infects OT, providing some natural control. However, these measures are effective only when the OT population is low. Chemicals such as pyrethroids and organophosphate insecticides, while efficient in controlling the pest, have disadvantages that include concerns about environmental safety and human health (organophosphates), and incompatibility with natural enemies (pyrethroids).
The development of alternative control measures is therefore crucial for managing OT populations in a safe and environmentally sustainable way. In this context, the present study evaluated the performance of several biopesticides for controlling OT attacks in dry bulb onions. Additional reduced-risk products were also evaluated.
Eleven different treatment schedules were assessed, using various combinations of the following agents: Botanigard ES (Beauveria bassiana conidia 11.3%), Delegate WG (spinetoram 25%), Entrust Naturalyte Insecticide (spinosad A/D 80%), Surround WP (kaolin 95%), Trilogy (neem oil extract), Requiem 25 EC (Chenopodium ambrosioides extracts 25%), Movento 240 SC (spirotetramat 22.4%), Carzol SP (formetanate hydrochloride 92%), Ripcord (cypermethrin 400 EC), Cyazapyr (cyantraniliprole 100SE), and Malathion (malathion 500EC).
The trial was conducted on a commercial dry bulb onion field in Berwick, Nova Scotia. Initial treatment applications were made in early July 2009, when the surrounding field reached an OT level of 1 per leaf. Subsequent applications were determined weekly by OT counts. When specific treatment plots reached the threshold of 1 OT per leaf, the next scheduled application was made, except for two of the treatments which received weekly insecticide applications. OT levels were monitored throughout the growing season in each treatment plot to identify decreases in populations. In late July and August, OT feeding damage from the inner 4 leaves of 5 randomly selected plants per treatment plot was rated on a 0-5 scale where 0 = no feeding damage, and 5 = total leaf surface showing signs of OT feeding.
The largest reduction in OT numbers and feeding damage was achieved with a weekly schedule of Movento, Carzol, Cyazapyr and Delegate, closely followed by a weekly schedule of Ripcord, Carzol, Cyazapyr and Malathion. Four applications of Delegate over the 7 week spray period also significantly reduced OT numbers and leaf feeding damage. Entrust applications in combination with Requiem provided some significant control, but was inconsistent throughout the season. A schedule of Botanigard and Delegate only provided one significant reduction in OT population near the end of the growing season. Weekly applications of Botanigard, Surround, Trilogy or Requiem alone, as well as a combination of Botanigard and Surround, provided no reduction in OT population or leaf feeding throughout the course of the trial at the tested rates of these products.
The results of this study suggest that Entrust, Delegate, Cyazapyr and Movento may have potential as reduced-risk pesticides for controlling OT in commercial dry onion fields. For more information about this study, please contact Heather Peill.
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