Aphids, or plant lice, are nearly always a problem, here in San Jose, California. This is particularly true when it comes to cabbage aphids.
Cabbage aphids (Brevicoryne brassicae) can wipe out a cabbage crop before it ever gets started. Native to Europe, this pest of cole crops is now found throughout the United States.
Vulnerable young cabbages
Cabbage aphids feed on the youngest, most tender parts of new cabbage, broccoli, Brussels sprouts, kale, and cauliflower. These pests love to feed on the innermost parts of cabbage and Brussels sprouts heads. Large colonies can stunt or even kill young plants. Heavy aphid feeding causes leaves to curl up, providing the pests with even more protection.
Cabbage aphid description
Like other aphids, cabbage aphids are soft-bodied sap-sucking pests that can reproduce at an alarming rate. While cabbage aphids are actually grayish-green, they look powdery blue to grayish-white because of a waxy covering. They are not difficult to see, since they live in dense colonies that can cover stems, new leaves, and entire plants practically overnight. Here in California, these pests produce live offspring year round.
What’s really amazing about these pests is that they produce an enzyme, in their head and throat muscles, that gets combined with defensive chemicals (glucosinolates) from their host plants, to create a "violent chemical reaction" that releases mustard oil. This “walking mustard oil bomb” defense is particularly effective against ladybug larva.
Controlling cabbage aphids
Prevention is key to cabbage aphid control. My cauliflower plants, which had been protected under row covers, were left untouched, while my cabbages and broccoli were hit hard. Once aphids are seen, you can often use a strong spray from the garden hose to dislodge them. If that doesn’t work, insecticidal soaps can provide some control. Since soap may be phytotoxic, especially on cabbage and Brussels sprouts, it is a good idea to apply them on a foggy day. Also, remove any weeds in the mustard family from the area. Cabbage aphids can hide out in the mustard and then return to your garden. Pesticides can be used, as a last ditch effort, but aphids are developing resistance to these chemicals and that can be a dangerous spiral.
Another problem with using pesticides against cabbage aphids is that those same chemicals also kill beneficial, predator insects, such as lady beetles, parasitic wasps, and the syrphid fly (hoverflies). These helpful insects are natural predators of caterpillars, imported cabbageworms, diamondback moths, loopers, and armyworms, which can cause other problems for your cole crops.
Monitor your plants every couple of days and be on the lookout for cabbage aphids!
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