CO-Horts Blog

Tuesday, August 31, 2021

Cabbage Pests

By Yvette Henson, San Miguel Basin Extension

It’s been a tough gardening year.  My seedling plant starts got damping off disease, resulting in the loss of most of them.  I also had fungus gnats in the soil my seedlings were growing in.  The cabbage seedlings that survived damping off, got aphids.  Before planting them, I rinsed them in soapy water and removed aphids by rubbing them off.

Cabbages usually grow well in my 8,400’ mountain garden and although I’ve never had much of an issue with aphids, this year there have been quite a lot.  The hot weather may have contributed to this.  However, the cabbages have grown and so I haven’t done much about the aphids except try to keep the plants as stress free as possible by watering them well.  I give them a light fertilization with a complete fertilizer like 5-5-5 at planting and again every 4-5 weeks.  The cabbages I have harvested, I’ve soaked in salty water and the aphids came off in the water.   Purple cabbages are reportedly less susceptible to aphid infestation than green cabbages so if you have problems with aphids, try growing purple cabbages. 

Aphids and cast skins on cabbage leaf
(there's even a mummified aphid)

I’ve had infestations in the past of imported cabbage worms (Pieris rapae) on my cabbages and other brassicas, so I’ve kept an eye out for the adults-- white butterflies with purplish-black spots on their wings but haven’t seen any flying around.  I also haven’t seen any of the velvety green caterpillars with a single yellow stripe down their backs and two broken lines along their sides on my plants. They overwinter in an inch-long chrysalis that matches whatever it is on.  They can have several generations a year.
Imported cabbage worm

I cover most of my raised beds with row cover fabric held up and off the plants by hoops made from recycled irrigation tubing. This can deter the cabbage worm butterflies (and other pests) from being able to lay their eggs on the plants. 

Cabbages growing in a raised bed with row cover fabric on hoops

This year, although I haven’t seen any imported cabbage worms, the row covers didn’t prevent cabbage looper moths (Trichoplusia ni) from finding a way inside the cover to lay their eggs on my cabbage plants. Unlike the adult imported cabbage worm, which is a butterfly, the adult stage of the cabbage looper is a brown moth.  The caterpillars are green with several light lines down their back and sides.  The easiest way I’ve found to distinguish them from the imported cabbage worm is their distinctive “inch worm” crawl.   They overwinter in a white webbed cocoon on the undersides of the leaves, in plant debris or the soil.  They also can have several generations a year.
Cabbage Looper and feeding damage on Cabbage Leaf

Both Imported cabbage worms and cabbage loopers feed on the leaves.   They can do quite a lot of damage, making the plants unsightly and weakening them.  Cabbage worms sometimes bore into the heads.  It’s unappetizing when you boil a cabbage and several caterpillars float to the top of the hot water.  

 You can treat the plants when the caterpillars of both cabbage worms and cabbage loopers are young with Bt, Spinosad or some other insecticide (follow the label) but don’t use a broad spectrum pesticide that can harm beneficial insects. Because I usually have less than a dozen plants, I simply check the undersides of the leaves each time I water the plants and remove them by hand. Covering with row cover does prevent at least some of the adults from getting in and laying eggs.

Even though my gardening year got off to a rough start and my cabbages have been infested with aphids and cabbage loopers, I have still had a good harvest of some nice cabbages.  

Savoy cabbage harvested August 25, 2021



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