Widespread Aphid Infestations In Winter Canola Across Western Kentucky
ZENAIDA VITORIA, FELIPE BATISTA AND DR. RIC BESSIN
PRINCETON, KENTUCKY
We visited five commercial canola fields in Graves and Marshall counties) and a research field in Caldwell County last week and observed turnip aphid populations at different infestation levels from field to field. Most canola fields are at 50-90% flowering stage at this time in western Kentucky (Figure 1). Turnip aphid reproduces rapidly and mainly attacks rachis and peduncle of the inflorescences, developing pods, and upper stem. This pest can potentially compromise canola yield when severe attacks take place at this vulnerable stage.
We observed infested plants distributed all over the field, on the edges and at any point inside the field. Heavy turnip aphid infestations can cause wilting of floral meristems and prevent further development of new flower buds (Figure 2 – red circles). Therefore, it is possible to spot damaged plants in the distance. Regular field scouting is key to detecting aphid infestations before they reach damaging levels.
Aphids Identification
Three aphid species are commonly found in canola: turnip aphid (Lipaphis erysimi), green peach aphid (Myzus persicae), and cabbage aphid (Brevicoryne brassicae). All may occur on leaves and racemes.
- Green peach aphid: pale green, around 1/8 inch, long and slender cornicles (2x cauda length), typically found on underside of leaves, colonies more scattered.
- Cabbage aphid: dark green, 1/12-inch, thick white waxy coating, short cornicles (shorter than cauda), dense colonies, usually found on upper leaves surface and racemes.
- Turnip aphid: dark green, 1/16-inch, light waxy coating, medium cornicles (1.5x cauda length), dense colonies, present mainly on racemes (Figure 3).
Scouting and decision-making recommendations
- Regularly visit the canola fields to scout for aphid populations.
- Walk the field in different directions, look out for wilted, yellowish, and stunted plants. The presence of honey dew, ants and sooty mold are also signs of aphid infestation.
- Look for aphids on inflorescences, they are visible with the naked eye. Clusters of turnip aphids are visible on the inflorescences and developing pods (Figure 3). Turnip aphids also dwell on the lower leaf surface, which would be an important place to check during rosette stage.
- Compare level observed to the Economic threshold.
Scouting should be based on visual inspection across multiple areas of the field, estimating the percentage of infested plants. The threshold for turnip aphid on canola is around 20% of plants infested with colonies of 25 or more aphids. If aphids are present but below threshold, increase scouting frequency to monitor population growth (twice a week if infestation is close to threshold).
Management
In most fields, infestation levels ranged from low to moderate and a significant presence of natural enemies was noted, including lady beetles (Figure 4), syrphid larvae (Figure 5), and parasitoids (both wasps and aphid mummies) (Figure 6). These beneficial insects help to slow population growth, reducing or delaying the need for insecticide applications. Unnecessary insecticide applications should be avoided when populations are below thresholds, especially considering the presence of active natural enemies in all evaluated fields.
If the infestation reaches 20% of plants, treatment may be necessary. Formulations with flonicamid or sulfoxaflor are reported to be more selective to preserve aphid natural enemies. Avoid applying pyrethroids for aphid control, as they are often more toxic to beneficial insects than to the target pest and may lead to aphid resurgence or secondary pest outbreaks. Always follow label directions and consult your local extension agent before making insecticide applications. ∆
ZENAIDA VITORIA, FELIPE BATISTA AND DR. RIC BESSIN
UNIVERSITY OF KENTUCKY