- Brevicoryne brassicae (cabbage aphid)
- Myzus persicae (green peach aphid)
- Lipaphis pseudobrassicae (turnip aphid)
IDENTIFICATION
Aphids are very small, soft-bodied pests. They have an oval to tapered body shape and two distinctive cornicles at the posterior end. The cornicles secrete different types of pheromones as well as a waxy substance that deters predators.
- Wingless cabbage aphids (B. brassicae) are nearly completely covered with grayish-white wax, which can be used as an identifying characteristic.
- Wingless green peach aphids (M. persicae) are light green. They tend to be less damaging in cole crops, but have a host range of over 300 different plants.
- Turnip aphids (L. pseudobrassicae) can be a problem in brassica seed crops, collards, and kale. They are also known to feed on cucurbits and solanaceous vegetables.
LIFECYCLE
Aphids overwinter as eggs in temperate climates. The rest of the year, they have a unique mode of reproduction that produces winged females (alate) and wingless females (apterae). Immatures are called nymphs and there are multiple overlapping generations per year. Populations usually occur as a mix of nymphs, winged, and wingless forms, as seen in the image below and this video.
DAMAGE & MONITORING
Aphids feed by piercing-and-sucking. This can cause localized wilting and yellowing of leaf tissue. Stunting of plants is common when infestations are high. Aphids are plant disease vectors and can transmit more than 15 important plant viruses, including mosaic viruses.
- Begin scouting new plantings immediately, because once infestations occur, they are hard to control.
- Walk fields and pull 10 leaves from a few different spots, examine
- Look on upper and lower leaf surfaces and in leaf folds of developing heads.
- Aphids can also occur on stalks and especially in leaf axles.
- Note the occurrence of aphid “mummies” – tan-colored, ‘puffy’ shells of an aphid mean that it has been parasitized by a beneficial wasp. If there are more mummies than aphids, it means that natural enemies are abundant and actively working to help control aphid populations; consider this before making a spray application.
MANAGEMENT
Biological: ‘Aphid wasps’ are tiny (2-3mm) parasitoids. When a female wasp lays eggs in the aphid’s body, larvae hatch and develop inside. The wasp larvae develop inside the aphid, which kills it. You may have seen aphid “mummies” – this tan-colored papery shell means that a beneficial wasp is developing within the aphid. A hole in the shell means the wasp has completed development and hatched out. Learn to recognize aphid mummies!
General predators such as ladybugs, lacewings, and syrphid fly larvae feed on aphids as well. Lacewing larvae are called ‘aphid lions’; estimates suggest that each larvae can consume 200 aphids per week.
Green lacewing larvae sometimes cover themselves with debris and are called ‘trashbugs’ – how fun would it be to see this ?
Cultural: Insecticidal soaps can be effective and should be timed accordingly to prevent damage to beneficial insects. Dislodging aphids with a strong stream of water can be useful in gardens. Crop rotation and removing debris post-season are both important strategies.
Chemical: Insecticides are important tools for commercial growers. Common options include cyantraniliprole, chlorantraniloprole, and spirotetramat. Surfactants must be used due to the waxy nature of both the pest and the crop hosts. Bt is ineffective on aphids, but using it for other brassica pests early in the season can help preserve natural enemies, which then persist to help control aphids. For more information, consult the PNW Insect Management Handbook
REFERENCES:
1. Jahan, Fatemeh et al. 2014. “Biology and life table parameters of Brevicoryne brassicae (Hemiptera: Aphididae) on cauliflower cultivars.” Journal of insect science vol. 14 284. doi:10.1093/jisesa/ieu146.
2. University of Minnesota factsheet
3. CABI factsheet for farmers
4. Review article of aphids in vegetable crops in India – new (2020)