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Canadian Organic Science Cluster Success Story: Managing a critical pest in Canada’s organic apple heartland
The rosy apple aphid is an important pest in organic apple orchards worldwide. The damage caused by this aphid not only affects the current year’s crop but also reduces the number of blossom clusters and consequently the crop on trees the following year. As a result growers experience economic losses that can reach up to $10,000 per acre in high value cultivars e.g. “Ambrosia”. Previous research on the control of rosy apple aphid focused on spring control using both conventional (chemical pesticides) and organic methods (dormant oil sprays). The latter were never very successful.
We designed a study to test if the application of fall (when the aphids return from their summer alternate host to the apples to lay their overwintering eggs) and spring sprays (when these eggs are hatching) of oils could be effective at reducing rosy apple aphid infestations. Researchers in Switzerland have developed a degree-day model for springtime rosy apple aphid phenology. This degree-day model for the spring and day length as a fall indicator were explored as possible tools that growers could use to effectively time both spring and fall sprays.
Oil sprays were applied sequentially both spring and fall over a six week period. Results from the first two years of trials show that based on timing, both fall and spring applications of oil can reduce populations of rosy apple aphids substantially when compared with controls. In the 2009/2010 trials approximately 90% fewer aphid-infested clusters were found in test plots with the most effective fall spray date. In the spring approximately 85% fewer aphid-infested clusters were found in test plots with the most effective spring spray date. In the 2010/2011 trials approximately 65% fewer aphid-infested clusters were found in test plots with the most effective fall spray date. In the spring approximately 75% fewer aphid-infested clusters were found in test plots with the most effective spring spray date. Previously, no controls had been targeted against the returning fall populations and the most effective spring sprays of oil were found to be those applied much earlier than the previously unsuccessful applications.
This is good news for organic apple growers. Until now there have not been any effective tools available for control of rosy apple aphids in organic apple orchards. We are now in our final year of trials and will be testing some combinations of fall and spring sprays as well. We have reported our results at meetings in British Columbia and at least a few organic apple growers in British Columbia and one organic apple grower in Ontario are going to use the degree day model to test spring oil sprays for rosy apple aphid this spring in their orchards.
© 2012, Organic Agriculture Centre of Canada (OACC)