What to do now
Mildest step first.
- Check the crown and the undersides of young leaves twice a week.
- Snap off heavily infested leaves and bag them; squash small colonies.
- Knock the rest off with a strong stream of water every few days.
- Leave bronze, puffed-up aphid mummies alone; wasps inside them kill more aphids.
How to recognize them
Cabbage aphids feed only on cabbage-family plants, including kale, collards, broccoli, Brussels sprouts and wild mustards. UC Statewide describes them as greenish-gray with a white, waxy coating, living in dense colonies on the youngest leaves and deep inside heads. The Pacific Northwest handbook notes the turnip aphid looks very similar but lacks the waxy bloom. North Carolina State Extension says both are most common in cool, dry weather and, because they feed on the undersides of leaves, often go unnoticed until numbers are high. Infested leaves crinkle, cup and curl, and heavy feeding can stunt or kill small plants. For aphids on other crops, see the general aphid page.
Why sprays miss
Leaves curl around the colonies as the aphids feed, and UC IPM notes that this, along with the dense, waxy masses, makes them hard to reach with sprays. A quick pass over the top of a kale plant leaves most of a colony untouched in the crown and under folded leaves. NC State advises covering plants completely, especially the undersides of leaves, because aphids shelter in pockets, crevices and buds, and says repeated applications are usually needed. Whatever you use, aim it into the center of the plant and up under the leaves, not just across the top.
Water, picking and natural enemies
Start without sprays. The Pacific Northwest handbook says home gardeners can often get effective control by washing aphids off with a strong stream of water; repeat every few days while they're active. NC State suggests squashing small colonies, or breaking off infested leaves and taking them out of the garden. Then look for help. UC IPM lists the parasitic wasp Diaeretiella rapae, lady beetles, syrphid fly larvae and fungal diseases among the cabbage aphid's natural enemies. Parasitized aphids turn into bronze or tan, puffed-up mummies, NC State notes; leave those on the plant. UC also cautions that natural enemies may not keep up when colonies are large or deep in the plant. Go easy on nitrogen: the PNW handbook notes aphid numbers tend to be higher on heavily fertilized crops.
Using insecticidal soap
Insecticidal soap kills the aphids it wets, but UC IPM rates it as only partial control on cabbage aphids and warns that higher concentrations can injure leaves, especially on Brussels sprouts and cabbage, so use the lower rate on the label. Spray in the cool of the evening, wet the undersides and the crown thoroughly, and repeat as the label allows. NC State lists insecticidal soap, pyrethrin and neem oil as organic options; check each label for how long to wait before harvest. The PNW handbook notes that most aphid sprays also kill natural enemies, so if mummies and lady beetles are increasing, hold off.
Washing the harvest and cleanup
Cabbage aphids are unpleasant but harmless to eat. NC State suggests washing harvested leaves under running water, or soaking them in soapy water and then rinsing with clean water, and notes the leaves are safe to eat even if a few aphids remain. After harvest, UC IPM advises destroying crop leftovers and removing related weeds such as wild mustards, which keep aphids going between crops. NC State adds that where winters are mild, cabbage aphids survive the cold, most often on collards, so a fall outbreak can keep growing for weeks unless natural enemies are already present.
Read the whole label first: it must list your crop, and its directions (amount, timing, gear, bees, days before harvest) are the law. If this page and the label differ, follow the label.
- KaleThe cold-weather workhorse that improves when everything else quits.
- Collard GreensThe heat-tolerant brassica that gets Southern gardens through the summer.
- BroccoliA cool-season brassica that heads up for a short window and then turns on you.
- Brussels SproutsA 100-day commitment that tastes best after the first hard frost.
- CabbageA long-maturing head that splits if you water it wrong at the wrong time.
- I have aphids on multiple plants — do I need to spray everything?Aphid outbreaks often crash on their own once lady beetles, parasitic wasps, and other natural enemies find them — water sprays and patience are often more effective than pesticides.
- How do I deal with cabbage worms on my kale and other brassicas?Bt kurstaki (Bacillus thuringiensis var. kurstaki) sprayed on the leaves is the most targeted control for cabbage worms — hand-picking and row cover are also effective without any spray at all.
- What is eating holes in my kale and cabbage leaves?Small round shot-holes suggest flea beetles; ragged large holes with frass (dark green droppings) point to cabbage worms (imported cabbageworm) — check both sides of leaves to identify which you have.