Friday, October 5, 2007

Organic Gardening Techniques Don't Always Work

I have not written about garden insects much this year like I did last year. Largely it is because last year's menaces did not repeat this year. I guess the Tomato Hornworms really were killed by the braconid wasps and the Blister Beetles really were chased away by their dislike of the horseradish plants. In both cases nature ran its course and I benefited from natural organic remedies without using any unnatural chemicals or poisons.

I really do believe in gardening organically. There is no room in my garden for chemical pesticides or fertilizers - Period. However, I'm not one to preach about it and I don't pretend that if you stay organic you will never have any problems. Sometimes it is quite the opposite and you have to be willing to lose an entire crop at times. That was the story this year with my broccoli.

Cabbage worms by the dozens destroyed all of my Spring broccoli, and it looks like my Fall broccoli will suffer the same fate. We only planted two plants this spring since we had so much last year that we couldn't eat it all. Since there were only two plants, I thought I could control the worms by hand-picking every day. After all, if you've ever looked up what to do about insects in an organic gardening book, most of the time it says to simply had pick them and destroy. This seemed easy at first because many of the worms are large and easy to see.

Of course, hand picking them all is easier said than done! The problem is that they start out so small and grow so fast. They are also very good at hiding right in front of you. Here's an example; how many cabbage worms do you think are on these two plants?

Would you believe 15? I know that it is too hard to tell from a little picture so lets zoom in and look at only 1 plant.

Now how many do you see? Seven, right? Does this help you see them?

And this picture was taken after I had already removed five or six worms! I thought I was finished until I looked closer.

Notice that I'm counting one that I already squashed on the raised bed wood on the lower left. I know it is a bit gross to discuss, but it was very interesting to see what happened when I distingished the worms in this way. As soon as I would kill a worm on the wood, an ant would come along and take the body.

It was fascinating to watch. Every cabbage worm carcass was dutifully carried away, each by a single ant.

That is a good illustration as to why I don't want to spray poisons on the plants to kill the pest insects. In this case, the spray would have killed these ants too. Chemical pesticides are not only bad for us to consume, but they kill or drive away earthworms and beneficial insects. To me, even though I lost this battle and got no fresh broccoli, it is worth it to maintain a safe and healthy soil and micro-climate.

As for the Fall broccoli, they too are infested with cabbage worms. Usually Fall broccoli is safe from the cabbage butterfly and worm but this year it is still hot in October - a record high 90 degrees as I write this! Next year I will cover all of my brassicas with poly-spun row covers to keep out the butterflies. This year I will continue to fight a losing battle and keep hand-picking the worms. At least it feeds the ants I guess.

It's really too bad that I have to kill these worms. They are actually kind of cute.

What am I saying?! They are garden pests and they are killing MY organic broccoli! That is a punishable offense indeed.



Hi Marc,

I have two suggestions about the cabbage worms. First is they are laid by butterflies or moths, and you can cover your plants with netting to keep them off.

I am a 100% organic gardener too, and in fact I don't use it myself, but many gardeners have good luck with Bt. Most people consider Bt organic. It is harmless to everything except caterpillars. Bt is a type of bacteria that damages the gut of caterpillars.

Since Bt is a bacteria that occurs naturally anyway in small quantities, so using it in your garden is not a lot different from say buying a box of ladybugs to eat aphids. Bt is harmless to humans, and you can use it all the way up until harvest. The only annoying thing about it is you have to reapply it after it rains, because it easily washes off.

We were talking about this a month or two ago on Skippy's Garden.

Anyway, good luck with the broccoli!

Robin (Bumblebee)

Yep, I agree with Marc. The netting over the row works nicely. I also find that I can grow broccoli, cabbages and such in the fall without the problem of bugs. They just attract too much attention from unwanted creatures in the summer months.

--Robin (Bumblebee)


Sometimes we have to loose a plant or plants that year due to bugs. I guess it comes with being organic gardeners.

Have you tried BT Marc?


HI Marc.

I also was inundated with green worms on broccoli and kale earlier this year. I made hoops and covered both plots with garden fabric. My neighbors asked if I was expecting a frost soon (in August!!??), but I persisted. The caterpillars are laid by a pretty white butterfly, and I had many flying over my garden.

Anyway, the fabric worked great. I recommend it. In late September I noticed the butterflies were gone, so I have now uncovered the plants. No holes! The kale is delicious, but my broccoli has another month to grow.


Thank you all for the suggestions. I have used row covers in the past to keep out the butterflies but last year I had no problems with them so I guess I was over-confident this year. I have read about BT but have never tried it. I'm still a bit leary about it but Patrick, you have talked me into it. That at least might salvage this Fall's crop. Next year I will go back to using the row covers.


That's interesting that you call them 'cabbage worms'. They look like the caterpillars from the cabbage white butterfly. Is this just the same thing called different names across the ocean?



The cabbage white butterfly are also sometimes called cabbage moths.

I was having a hard time with this in my post too, because I think in part this might be a difference between north and south US, as well as American and UK English. I've completely lost track of what they are called where.


Excellent pictures! You should start a blog about how you have trained your ants to clean up your garden like that. Impressive. :)


Matron, do you call them cabbage caterpillars? That would actually make more sense because scientifically they are caterpillars and not worms. I've always heard this insect called a cabbage worm and my best garden insect guide, Garden Insects of North America, calls it a cabbageworm (Pieris rapae), the larva of the cabbage butterfly a.k.a. cabbage white.

Patrick, the book also mentions a related species, the southern cabbageworm (Pontia protodice) larva of the checkered white, which looks similar to the cabbageworm.

It is interesting that things are called by different names in different places. I guess thats why we need to refer to the Latin name if we want to be perfectly clear about what species of insect or flower we are talking about, but who actually does that?


According to Wikipedia:

The Cabbage Moth (Mamestra brassica) is a common European moth that is a pest to cabbage plants. This same article says the Small White butterfly is sometimes incorrectly called a Cabbage Moth in the US.

Small White Butterfly (Pieris rapae):

This is present almost everywhere in the world, and leaves 'caterpillars' on cabbage plants.

Large White Butterfly (Pieris brassicae):

Is common in parts of Europe, Africa and Asia. It also leaves 'caterpillars'.

The term Cabbage Worm:

is used by agriculturalists to describe the caterpillars above, as well as others.

Perhaps the names you use are not only dependent on where you live, but also if you are an agriculturalist or what kind of species you are talking about.

As far as I'm aware, Bt works for most caterpillars!


Great info Patrick!

I like the way you ended it too - as gardeners, maybe we don't have to care exactly what species of pest insect we are dealing with, as long as we know how to control them! In this case Bt is the answer for killing the existing problem and row covers are the answer to prevent future infestations.

Bare Bones Gardener
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Hey Marc! If I could jump in here... It may be too late, but i just discovered you!
I just wanted to remind you that BT kills ALL catapillars, therefore killing all potential butterflies that come in contact. That's why I use row cover. Here in TX. we grow broccoli in the fall, but we still get cabbage worms, and I hate picking those dadgum things off! You flip over a leaf and there are dozen of tiny little babies! Yuck. I wish I had your friendly ants... we have fire ants here and they'd carry ME off, if they could. :)
BTW - I'm an old KY. girl! I use to live in MT.Sterling many moons ago. I've still got family there.
Love the blog! Great pics too.


The grubs for the cabbage moth and cabbage butterfly are totally different...and the moth and butterfly are different. They are both common to Australia. I think gardenwiki shows the lifecyle photos.They are both pollinaters...

Its not entirely a negative as it will bring the lacewings and ladybeetles, parasitic wasps and suchlike if you want a more permanent solution for your garden.

I'm definitely with Curtis LOL. I'm thinking of interplanting flowers with vegies cottage-garden- style...not for the beauty, but for the predators who happen to be omnivores and must have nectar.


Yes, it is true that Bt will kill most common caterpillars.

Bt however works by damaging the gut of the caterpillar, so the caterpillar has to eat it first. If you put Bt on your plants, and a caterpillar comes along and doesn't eat them, the Bt won't harm the caterpillar.

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