Description of the Pest
European asparagus aphid is a small, blue-green to gray-green aphid about 0.06 inch (1.5 mm) long. It is often covered with a powdery wax. Unlike most aphids, the cornicles of European asparagus aphid are reduced to practically invisible openings on the abdomen. The cauda, a projection at the very rear tip of the abdomen, is relatively long compared with other aphid species, and has sides that are nearly parallel. The antennae are short.
The wingless forms of the aphid likes to feed where the needles of the fern attach to the petioles. Their small size and coloration make them difficult to spot even upon close examination. Winged forms in very large numbers may appear as a large cloud. The aphid overwinters as eggs that have been deposited on the old fern or in cracks in the soil.
Damage
European asparagus aphid is an economic problem primarily in the southern Sacramento Valley and the northern San Joaquin Valley. Damage from European asparagus aphid comes mostly from the toxin it injects into the plant when feeding. The toxin causes shortened internodes on subsequent growth, resulting in a tufted appearance that is called bonsai growth. While other factors can cause a limited amount of this type of growth distortion, heavy European asparagus aphid infestations produce this distortion profusely. Heavy populations also produce massive amounts of honeydew that may attract ants.
Feeding by European asparagus aphid causes more damage to the subsequent year’s crop because it compromises the vigor of the crown. After 1 or 2 years of feeding by this aphid, the asparagus crown weakens and dries out. The toxin may also delay the bud break in spring, only to then cause an eruption of small spears. The damage is especially pronounced on newly established or weak plantings, and in seedling beds.
Management
Clean fields of crop debris and conserve natural enemies.
Biological Control
Natural enemies, especially parasitic wasps and lady beetles, help control European asparagus aphid. Most parasitoids, such as Diaeretiella rapae, are most effective on heavy infestations, but only after the damage is done. A species of Trioxys imported and released to control European asparagus aphid has had little success to date. General predators, such as the convergent lady beetle, may feed on some European asparagus aphids, but the pest's rate of reproduction can overwhelm the predators’ impact. Encourage natural populations of parasitoids by delaying pesticide applications where possible.
Cultural Control
Mowing, chopping up, and then incorporating ferns during the dormant season may substantially reduce the number of eggs in the area.
Organically Acceptable Methods
Cultural and biological control, and sprays of mineral oil (narrow range oil) and pyrethrins are acceptable for use in a certified organic crop.
Monitor field edges regularly. European asparagus aphid populations start very slowly and in widely dispersed patches, then seem to nearly explode. Populations often begin near field edges, so monitor the edges regularly whenever fern is present. It is best to collect plant samples and then shake or beat them on a hard, light-colored surface (such as the side of a white 5-gallon bucket or hood of a pick-up) to dislodge both the aphids and their natural enemies. Visual inspection of the ferns is not reliable, even for experienced scouts.
No definite threshold has been established; any threshold will vary with the condition of the field and time of the season. Many infested plants indicate a worse problem than many aphids on a few plants. A small infestation earlier in the season is more likely to become a problem. Waiting to see plant distortion or large amounts of white cast skins under plants may allow numbers to reach damaging levels before the infestation is detected. Treat when numbers of aphids increase rapidly and there is not enough natural enemy activity to suggest that the aphids will be controlled in a few days.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites 4 | Predators 5 | Parasitoids 5 | Residue duration 6 | Leaching(fish) 7 | Adsorbed runoff(fish) 8 | Solution runoff(human) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
Assail 70WP | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
4A |
1.1–2.3 oz | 12 | 1 | Use a high-water volume spray to get goo... | broad | — | — | — | moderate | very low | very low | low | very low | low | 05/2025 | ||
|
|
Sivanto prime | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
4D |
7–14 fl oz | 12 | See comment | Use a high-water volume spray to get goo... | — | — | — | — | — | very low | low | low | very low | low | 05/2025 | ||
|
|
Organic JMS Stylet-Oil # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
UNM |
3–6 qt/100 gal water | 4 | 0 | Although narrow range oil (mineral oil)... | broad | low 13 | low | low | short | very low | low | very low | very low | very low | 05/2025 | ||
|
|
Seville | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
9B |
2.75 oz | 12 | 170 | Apply to asparagus ferns after harvest h... | narrow | low | low | low | short | very low | low | low | intermediate | high | 05/2025 | ||
|
|
PyGanic EC 1.4 II # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
1–4 pt | 12 | 0 | Air blast applications are more effectiv... | broad | — | moderate | moderate | short | low | low | high | very low | intermediate | 05/2025 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- # a b Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 ↩ Risk of harm to predatory mites. Toxicities are generally to western predatory mite, Galendromus occidentalis. Where differences have been measured in toxicity of the pesticide-resistant strain versus the native strain, these are listed as pesticide-resistant strain or native strain.
- 5 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 6 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 7 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 12 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
- 13 ↩ Rating depends on application rate used.
UC IPM Pest Management Guidelines: Asparagus
UC ANR Publication 3435
E.T. Natwick (emeritus), UC Cooperative Extension Imperial County
B.J. Aegerter, UC Cooperative Extension San Joaquin County (European Asparagus Aphid)
Acknowledgement for Contributions to Invertebrates
R.J. Mullen, UC Cooperative Extension San Joaquin County
W.E. Chaney (emeritus), UC Cooperative Extension Monterey County
C.F. Fouche, UC Cooperative Extension San Joaquin County
