I have been struggling with the mysterious death of my broccoli, and then cabbage, for a few years now. At first, I thought the ants had to be doing it, since they were the only thing I could see. Finally, this year, I learned about cabbage maggots. I had no idea that there is a whole category of root maggots from flies that lay their eggs at the base of plants for the larva to feed off of the roots. Understandably, this either kills the plants outright, or stresses them in ways that make them vulnerable to other pest and diseases.
Everything I read and see about cabbage maggots fits with what is happening to my plants. The main things that threw me off from finding this before were:
- no one mentioned the leaves turning purple, like many of my plant leaves do
- I could not see any insects in the soil, other than ants and pill bugs
- nothing I did seemed to help
I made a short video showing what has been going on with my broccoli and cabbage so far this spring. I dug around many plants trying to find the cabbage maggots, and I think I found a few of them once in the soil, but I couldn’t get a photo of them. There were not any actively on the roots of any of the plants at this time that I could see. Since it has been about 3 weeks since I began seeing plants suffer, that makes sense according to their life cycle. (see links below)
Below are a few very helpful links for learning about cabbage maggots. The highlights are:
- the cabbage fly looks very much like the common housefly
- eggs are laid at the base or in cracks near the plant after it is 2-3 weeks old
- the maggots live and feed for about 3 weeks
- the worst infestation (and damage) usually occur in spring, because they prefer cool, moist conditions
- they are not easily affected by pesticides, prevention is the best cure
Canola Council of Canada (scroll to nearly the bottom for specifics on the cabbage maggot)
After doing research about these pests, I have some hope that the broccoli I planted a couple weeks ago will fare better. The thing with cole crops is that once the heat hits (like, next week) there will be serious infestations with aphids. The younger plants may be more vulnerable to that.
I have tried row covers before, to keep off cabbage moths, but found the covers to be tedious. I couldn’t weed easily, I couldn’t evaluate the plants, and the moths still got under them! I will consider a different sort of protective collar around the seedlings next year. I may research oil or vaseline at the base of the plants to smoother the eggs. Whatever I do, it needs to be done before I begin to see damage to the plants, because then it is too late, unless the ants harvest enough of them to save the cabbage and broccoli.