Saturday, May 25, 2013

How to Control Cabbage Root Maggots (and other pests) without Pesticide

A cabbage, in it's natural, home-grown garden environment is truly a thing of beauty.  Unlike the neatly trimmed green orbs we find in the grocery store, in their natural garden state they more resemble a giant green rose.  Some can grow as much as 3' across.  They range in color from pale green to blue-purple.
Nutritious and versatile, both Western and Eastern cultures have grown cabbages for thousands of years.  I suppose I could blather all day about cabbages and their many cousins:  broccoli, kale, turnips, radish, cauliflower, kohlrabi and even arugula but what I really want to offer up here in this post is help for the home  grower.

Can you see the tree frog?.....  They love to hide in cabbages.

 Cabbages and most all brassicas are a host to many pests.  The worst of the lot (at least here on the West Coast) are Cabbage Root Fly Maggots and Cabbage Moths.  Though I learned a fair amount of gardening skill from my grandparents, one thing I no longer do is douse any of my plants with any sort of pesticide.  I don't even use bacillus thurengiensis, which is a natural bacteria that will kill caterpillars, but is indiscriminate and will kill ANY caterpillar--even those who pose no threat to your cabbages.

The most insidious pest I have encountered here in the Portland area is the Cabbage Root Fly Maggot.  These little red-eyed bastards will come along in the Spring and then again in the Fall to lay their eggs at the base of the stems of cabbages and other brassicas.  Though the adult flies themselves never take a single bite of the plant which they choose to lay eggs on, the tiny little oblong white eggs will hatch within days into little hungry maggots who will munch away at the roots of the host plant until there is nothing left.  When I first encountered a very bad infestation out on Sauvie Island, I was actually lifting wilted cabbage starts out of the ground that had absolutely no roots left.

The tiny eggs of a cabbage root fly, on my finger tip. 

Eggs, found where they were laid by the adult.  These will hatch in 2-3 days and burrow down to start eating first the fine rootlets and then the main stem.  Maggots will increase in size 20x or so from egg stage before entering pupae stage.

I recall my initial research of how to control cabbage root maggots was pretty dismal.  I think there was one, fairly benign pesticide which was supposed to work okay but I didn't use it (I no longer recall the name).  In one of my gardening books I found a description of how to use cut-out disks of tar paper that you would slit one side and slip it around the base of the stem of the plant to serve as a shield against the hatching maggots (which can't burrow through the tar paper). At first, the tar paper method sounded great but it didn't really work well for a couple of reasons.  First, we must have a particularly crafty strain of Cabbage Root Flys here around Portland, as I found fly eggs UNDER, not on top of the tar paper.  Some of the flies had actually crawled under the paper and deposited eggs on the soil, thus rendering the paper pretty much worthless as a shield.  Secondly, I found that the tar paper collars were restrictive for the cabbage plants, which didn't seem to grow as well with the collars around them.   I think it makes their roots too hot and dry.  So, after some thoughts on my own, I came up with an idea of covering the entire plant.

There are many kinds of crop covers such as Remay, and such out there that can achieve adequate protection for brassicas with the added bonus that it will protect them from ALL flying insects.  However, after trying them out I found them fussy and fiddly to deal with.  They wound slump in the rain, blow off in the wind and were generally a big pain in the ass to deal with when I needed to get under them for weeding and fertilizing.  They also had a tendency to get really HOT and if you have much experience with growing brassicas you will know that HOT is not your friend.

So, I came up with this idea--I took some screen door mesh, folded it this way and that and produced free standing "tents" that would not blow away in the wind, sag in the rain or retain heat.  An added bonus is that you can also reused them year after year.

Newly planted starts with covers.

Same plants, a few months later, covers removed.  These are now large enough to handle a few bugs.

Now, of course this method of covering the young brassica starts isn't as attractive as an uncovered garden with pretty rows of plants.  But, the nice thing is that by the time the starts grow large enough (and beautiful and pest-free) the cabbage root flys have usually dissipated with the warmer weather.  Also, a half grown cabbage can actually stand to endure a few lingering root maggots as the plants are now large enough with roots deep enough to withstand some chewing.

So, my fellow cabbage lovers......if you have happened upon my barely-read-by-anyone blog seeking help with your battle with root maggots, below is a basic "how to" for making covers.

  1. Get yourself some metal screen mesh.  It needs to be metal so that it will hold it's shape.  Aluminum is okay but the old-timey steel mesh is the best.  It should be at least 36" wide.
  2. Cut a length of screen to cover 3-6 plants.  I plant my cabbages about 18" apart, so if I want a "tent" for four then I need 72" plus another 20" so that the ends can be crimped together.  Also bear in  mind that the longer you make your tent the more difficult and unwieldy it will be to get it in position over your plants.
  3. Fold the screen lengthwise into thirds.  Then lightly fold lengthwise in half (this forms the peak of the tent).
  4. While folded in half, crimp together the ends of the tent.  I do this by folding 1/2" forward and then back on itself 3-4 times and then using pliers to crimp the fold solid.  If you're nor already wearing gloves at this point, I would now put them on.  The ends can also be sewn shut with wire.
  5. To get the tent to stand up, you will first need to fold down last  3-4" of the ridge on either end. Then stand the tent up in position and work it this way and that until it stands open on it's own.
So, there it is.  A final tip for using your tent:  If your ground is lumpy or uneven and you have gaps under your tent, don't ignore them, as flies will find a way in.  Simply hill up a little dirt where needed.  

I've been using these covers for three or four years now.  I've since found that they also work well for covering beets and chard if you are troubled with leaf miners.  They also offer some protection from

Happy cabbages....

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