Prepared by Dr. John Gavloski, Field Crop Entomologist, MAFRD Crops Knowledge Centre
Potential Risks (costs):
- Increase in selection pressure to develop resistant insect populations if technology is overused.
- Potential increase in secondary pest populations
- Potential non-target impacts of the insecticide
- Increased cost to producer
- Reduced injury to crop from economic populations of insects that may be managed by insecticide
- Potential increase in early-season vigour of the crop under some growing conditions.
When all components of the equation are considered, and the science to support all the components, a neonicotinoid-based seed treatment is most likely to be beneficial when there is a high risk of flea beetles (in canola), wireworms, or seedcorn maggots causing economic damage to the crop. Using neonicotinoids as “insurance” if the risk of damage by these insects is low, is not likely to be the most economical choice in most years.
Regarding the potential increase of secondary pests, this is probably of greatest concern in corn and soybeans in drier years, where neonicotinoid seed treatments can potentially increase the risk of spider mites (Henry and Szczepaniec. 2013. Ent. Soc. America Ann. Mtg).
Regarding potential vigour-effects of neonicotinoid seed treatments, there are studies that do show some increased early season-vigour, regardless of whether insects are present, and other studies where this vigour effect did not occur. So a potential increase in crop vigour may occur, but may be dependent on growing conditions. Using a neonicotinoid-based seed treatment for the primary purpose of increasing seedling vigour may not be the best use of the technology either economically or sustainably. In a risk/benefit analysis, the 4 potential costs mentioned above need to be weighed against a potential increase in early-season vigour when deciding on a seed treatment. The other factor, and possibly the most important in the equation, is what is the risk of insects that the seed treatment may control (in Manitoba this would be flea beetles (on canola) or wireworms or seedcorn maggots).
In Canola: There are currently no seed-treatment alternatives to neonicotinoid insecticides (Lumiderm is currently applied with a neonicotinoid seed treatment). Flea beetles are a chronic and potentially serious pest of canola. Thus neonicotinoid-based seed treatments will likely remain an important management tool until alternative seed-treatments are available.
In soybeans and corn: Reduction in damage by wireworms and seedcorn maggots may occur if populations are high. Reduction in risk from soybean aphids would also be a consideration in some parts of North America, but not likely in Manitoba because the residual effect capable of providing control reaches levels that would be ineffective at killing aphids between 35 and 49 days after planting (McCormack and Ragsdale, 2006: Crop Management; Johnson et al., 2008. J. Econ Entomol. 101: 801-809; Tomizawa and Casida, 2003. Ann. Rev. Entomol. 48: 339-364). So decisions on seed treatments in these crops in Manitoba, as well as other pulse crops, would most appropriately be based on the risk of wireworms or seedcorn maggot.
In Small grain cereals: Decisions on whether a neonicotinoid-based seed treatment should be considered in these crops in Manitoba would most appropriately be based on the risk of wireworms.
In Potatoes: Wireworms can be a big concern and some control of other insects such as Colorado potato beetles is possible. Neonicotinoids will likely continue to be used quite extensively until other seed treatment or in-furrow options are available. A cautionary note, however, that Colorado potato beetle resistance to neonicotinoids has been documented in some parts of North America (Szendrei et al. 2012. Pest management Science. 68: 941-94).
Through a responsible use program and careful attention to how seeds are applied, many of the risks of neonicotinoid insecticides can be minimized. What commodity groups, and possibly even the companies that market neonicotinoid seed treatments, need to be concerned with is the overuse of the products when risk of potential threats the seed-treatments can control are low, and that all efforts are made to reduce the drift of dust from seed-treatments when planting corn and soybeans.