Early colonisation of canola by green peach aphid

Green peach aphid has arrived a little too early on canola grown from imidacloprid treated seed.

Green peach aphid (Source: cesar)

 

Last year cesar and CSIRO scientists confirmed the development of resistance to neonicotinoid insecticides in Australian green peach aphid (Myzus persicae, GPA) populations. The upside to this news was that the type of resistance detected was not the worst case-scenario. Essentially there are two main types of insecticide resistance that GPA populations can develop: target-site resistance and metabolic resistance. Target-site resistance is the real baddie as it results in complete insecticide ineffectiveness and control failures. This is the type of resistance that GPA has developed to synthetic pyrethroids (e.g. alpha-cypermethrin) and carbamates (e.g. pirimicarb). Metabolic resistance, on the other hand, is the lesser of two evils. When a population acquires this type of resistance, they can detoxify the insecticide and make it less effective. We have seen GPA develop metabolic resistance to organophosphates (e.g. dimethoate) and more recently, neonicotinoids (e.g. imidacloprid).

While it is difficult to predict what metabolic resistance to neonicotinoids means for canola seed treatments containing this mode of action, we anticipate a reduction in the length of protection that is offered. This season we have received reports of GPA colonising canola cotyledons grown from seed treated with imidacloprid from Deniliquin and Finley in the NSW Riverina. With the help of growers and agronomists we have received samples of these aphids which will be tested for their resistance status. We suspect they will be found with resistance to neonicotinoids.

Green peach aphid numbers are now likely to decline due to the increasingly cold and wet conditions in most regions. Insecticides should only be applied when necessary. Given the insecticide resistance issues affecting GPA, effective management begins with correct species identification. Cabbage aphid (Brevicoryne brassicae) and turnip aphid (Lipaphis erysimi) can be mistaken for GPA. Don’t hesitate to contact us if you require assistance distinguishing aphid species.

GPA are often confused with turnip aphid (left) and cabbage aphid (right) (Source: cesar)

 

To reduce the risk of insecticide resistance, rotate insecticides from different chemical groups, avoid the use of broad-spectrum insecticides, and apply appropriate insecticides only after careful monitoring. Growers and advisors are encouraged to download, and follow, the GPA Resistance Management Strategy to minimise the further development of resistance.

If you are a grower or agronomist and suspect a reduced level of efficacy in insecticide treated seed, we’d love to hear from you. 

For more information contact:

Dr Siobhan de Little, cesar

p: (03) 9349 4723

e: sdelittle@cesaraustralia.com