Aphids on Kale: Identifying Cabbage Aphid and Managing Heavy Infestations
The cabbage aphid (*Brevicoryne brassicae*) is the primary aphid on kale and other brassicas. It is significantly different from aphids on other vegetables in one important way: it secretes a waxy coating that makes it more resistant to water blasting and soap sprays than other aphid species. A.
—- title: "Aphids on Kale: Identifying Cabbage Aphid and Managing Heavy Infestations" slug: aphids-on-kale hub: problems category: "Problem-by-host" description: "The cabbage aphid attacks kale in dense, waxy colonies that resist water blasting. Here's how to identify it, assess damage, and choose controls that work." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 7 scientific: "Brevicoryne brassicae" —-
The cabbage aphid (Brevicoryne brassicae) is the primary aphid on kale and other brassicas. It is significantly different from aphids on other vegetables in one important way: it secretes a waxy coating that makes it more resistant to water blasting and soap sprays than other aphid species. A gardener who has successfully managed aphids on roses or tomatoes with a water hose will find that the same technique is less effective on a dense, waxy cabbage aphid colony on kale.
Identification
Per UC IPM, cabbage aphids are:
- 1.5–2.5mm long
- Gray-green to powdery gray in color (the waxy bloom gives them a dusty appearance)
- Found in dense, compacted colonies on undersides of leaves, inside leaf folds, and on developing heads
- Distinguished from other brassica aphids by their waxy grayish appearance
Colonies are typically found on the undersides of lower leaves first, then spread upward as the plant is increasingly colonized. The waxy coating that coats both the aphids and their eggs makes them resistant to physical removal.
Ants attending colonies indicate high honeydew production and active, feeding colonies. Inspect undersides of all kale leaves when ants are observed.
Life Cycle
Per Cornell Cooperative Extension, cabbage aphids overwinter as eggs on plant debris and weedy hosts in the brassica family. Spring populations build through rapid parthenogenetic reproduction — females produce live young without mating. In warm weather (70–80°F), a generation completes in 10–12 days.
Two population peaks typically occur in the Northeast:
- Spring: As temperatures warm in April–May; populations build on spring kale plantings
- Fall: More severe infestations on fall kale and overwintering kale; populations peak in September–October before cold terminates them
Fall infestations tend to be heavier because natural enemy populations (ladybeetles, parasitic wasps) have declined by late season. Per Penn State Extension, this is a consistent pattern across the mid-Atlantic: fall brassica aphid populations are more persistent than spring populations.
Damage Assessment
Per Penn State Extension, cabbage aphid feeding causes:
- Yellow, distorted leaves at infestation sites
- Curled or folded leaf margins (aphids shelter inside the folds)
- Honeydew and sooty mold accumulation
- Premature leaf senescence under heavy pressure
On kale grown for harvest, the more immediate consequence is palatability: aphids inside leaf folds are difficult to wash off, and dense colonies covering leaf surfaces make the leaves unpleasant to eat even when the structural damage is minor.
Heavy infestations on young transplants or plants under 6 inches can stunt growth significantly. Established plants with multiple leaves tolerate moderate infestations without yield loss.
The Waxy Coating Challenge
Per Clemson HGIC, the waxy secretion on cabbage aphids serves as a physical barrier. Water blasting — effective for removing 70–90% of aphids on roses or tomatoes — removes far fewer cabbage aphids because the waxy coating adheres to leaf surfaces and the colony structure.
insecticidal soap must penetrate the wax to kill aphids on contact. To improve penetration:
- Use soap at the higher end of the recommended range (2–2.5% potassium salts of fatty acids)
- Add 0.5% isopropyl alcohol to the spray mix to break down the waxy surface (check product compatibility first)
- Ensure complete coverage, including inside leaf folds where colonies shelter
Even with optimized soap application, 100% kill of a dense, established colony is unlikely in a single application. Per UC IPM, 2–3 applications at 3–5 day intervals are typically necessary to collapse a cabbage aphid colony.
Management Methods
Early Detection and Removal
Weekly inspection of leaf undersides starting at transplanting allows catching colonies when small. A colony of 10–20 aphids can be crushed by hand or removed with a water blast. A colony of 1,000+ aphids requires chemical control.
Insecticidal Soap
Per Clemson HGIC, insecticidal soap at 2% concentration is effective on direct contact with cabbage aphids when coverage is thorough. Apply in early morning; spray under and between all leaves. Repeat at 3–5 day intervals.
neem oil
Per NC State Extension, neem oil (azadirachtin-based products) disrupts aphid molting and reduces reproduction. Useful as a supplement to soap application in heavy infestations. Apply no more than every 7 days.
Pyrethrin (Botanical Insecticide)
Pyrethrin (derived from chrysanthemum flowers, distinct from synthetic pyrethroids) provides rapid knockdown of aphids with short residual activity. Per UC IPM, pyrethrin kills aphids and most beneficials on contact but breaks down within 1–2 days, allowing natural enemy recolonization. It is the most effective fast-acting botanical option for heavy infestations.
Resistant or Tolerant Varieties
Per Cornell Cooperative Extension, some kale varieties show lower aphid susceptibility than others due to leaf surface wax chemistry. 'Lacinato' (Dinosaur kale) and flat-leaved varieties tend to be less preferred by cabbage aphid than heavily curled varieties like 'Winterbor'. Less leaf surface for colony establishment on smoother leaves is one reason.
Cultural Controls
- Remove plant debris from previous brassica crops that harbors overwintering eggs
- Rotate brassicas to different beds each year (reduces local aphid overwintering egg population)
- Delay fall kale planting by 2–3 weeks to miss peak aphid flight periods in early September
Natural Enemies
Per Penn State Extension, key natural enemies of cabbage aphid include:
- Diaeretiella rapae (a parasitic wasp specific to brassica aphids) — very effective; parasitized aphids become golden-brown mummies
- Ladybeetles and lacewing larvae
- Parasitic fungi (Pandora neoaphidis) cause population crashes in humid conditions
Mummified aphids (gold-brown, swollen) indicate Diaeretiella rapae is active. At this point, reduce soap applications — the biological control is working and intervention may be counterproductive.
Common Problems
| Symptom | Cause | Fix |
|---|---|---|
| Dense gray-green colonies inside leaf folds | Established cabbage aphid colony | Soap at 2–2.5%; repeat 3x at 3–5 day intervals |
| Soap spray not killing aphids | Waxy coat repels water-based sprays | Add 0.5% isopropyl to spray; ensure complete coverage |
| Yellow, distorted leaves at growing tip | Heavy aphid pressure on new growth | Act immediately; young tissue most vulnerable |
| Gold-brown mummified aphids | Diaeretiella rapae parasitism | Reduce spraying; allow parasitism to proceed |
| Heavy infestations only in fall | Later natural enemy decline + aphid reproduction | Use floating row cover over fall kale; plant later to miss peak flight |
Frequently Asked Questions
Is kale with aphids safe to eat after washing?
Per Cornell Cooperative Extension, kale from aphid-infested plants is safe to eat after thorough washing in cold water with gentle agitation. The waxy coating on cabbage aphids means they do not penetrate leaf tissue. However, dense colonies inside curled leaves may be difficult to remove completely even with thorough washing. Soaking leaves in cold salt water for 5–10 minutes encourages aphids to release and float free.
Why do my fall kale plants always get worse aphid problems than my spring plants?
Per Penn State Extension, this is a consistent observation across the mid-Atlantic: natural enemy populations that reduce summer aphid pressure (ladybeetles, parasitic wasps) decline by late September, leaving fall brassica crops more vulnerable. Fall planting timing — waiting until late August rather than early August — can reduce aphid severity by placing the crop's early growth period after the peak aphid flight window.
Can I use floating row cover to exclude aphids?
Per UC IPM, lightweight row cover (0.9 oz/yd² or 1.5 oz/yd²) provides physical exclusion of winged aphids. Apply immediately after transplanting and secure all edges to the soil. Row cover does not prevent aphids that were present on the transplants themselves — inspect transplants before covering. See also: Aphids on Tomatoes and Aphids on Roses.
When should I remove heavily infested leaves rather than spray?
Per Clemson HGIC, when more than 50% of a leaf surface is covered by an established colony and the plant has other healthy leaves, removing and bagging the infested leaf is more efficient than repeated spray applications. Do not compost heavily infested material in a cold pile — a hot compost pile (140°F+) kills aphids and eggs; a cool pile does not.
—-
Recommended gear: Best Floating Row Covers for Pest Exclusion (2026) — our buyer's guide covering picks for every budget, ranked by Extension publication consensus and personal use.
Sources
- UC IPM — Aphids
- Penn State Extension — Aphids
- Cornell Cooperative Extension — Vegetable Pest Management
- NC State Extension — Integrated Pest Management
- Clemson HGIC — Aphids