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Radish Maggots – Getting to the Root of the Problem

May 12, 2010

For those of you who have brushed off the idea that crop rotation is important, I’ve got a story to tell that may change your mind.

Maggot Infested Radish

Maggot Infested Radish

Sure, it’s fun to dabble with a veggie garden space. It seems easiest to build a raised bed and just mix in a few of your favorite summer veggies and see what happens. For a few years growing a mix of cucumbers, tomatoes and kale in the same bed may work out great. But woe to the gardener who does it for long. Read on to learn from my early mistakes that hearken back to years when being enslaved to a high-tech desk meant my forays into veggie garden were haphazard at best. The cumulative effects of my dabbling left me with quite the scare and a big chore to get to the root of the issue.

Here’s the deal: when we bought our house years ago one of our first gardening projects was to dig out one section of grass and install two raised beds for veggies. Yay for us, right? Well, we did a few things right and several things wrong. Here we go with a few true confessions & video evidence of the investigation getting to the root of the problems:

Right: We did build the beds out of clear, 2×10 cedar. Those boards, now over 10 years old are just now beginning to decay.

Right: We did amend the sandy native soil with composted mulch over the years – ranging from Cedar Grove Compost to Fertil-mulch to Chicken ‘n Chips to cover crops like vetch and fava beans to Zoo Doo to our own worm mulch to applications of freshly, brewed compost teas.

Raised Beds Planted with Radish & Beet & Marigold

Raised Beds Planted with Radish & Beet & Marigold

Right: We did install drip irrigation to make our watering life easier.

Right: We did install hoop houses to extend the growing season.

Right: We did do soil testing to determine nutrient info, pH detail and even texture detail, but see the “wrong” section on this subject, too!

That all sounds great, right? But now for the wrongs…

Wrong: We did use fast release, synthetic liquid fertilizers in the beginning and then migrated to slow release synthetic fertilizers and finally we moved to slow release natural organic fertilizers.

Wrong: We didn’t test the soil at a lab for true analysis for many years. After doing so, we found that our potassium rates had accumulated to very high levels. So much for using general fertilizers and hoping for the best!

Wrong: We did not rotate crops in the beginning. Like many who dabble in veggie garden but don’t have the time, knowledge or inclination to manage a good set of rotating crops, we threw in a cucumber here and a tomato there.

We’ve seen the decline in crop performance over the years. And, this spring, I began to see what I believe to be the build up of crop pests that can occur due to poor land management. (To be honest, these problems can happen even if you are doing things right, but I only have myself to blame here.)

The first thing I noticed was what appeared to be tunnels under the soil level. Yet, the root crops weren’t crashing. Nothing from down under was demolishing them. Yet, if I put weight on certain areas of the soil, it would simply collapse. And, no mounds or exit holes appeared. It was a bit of a mystery.

Given that my crops were failing and I feared an infestation of a hard-to-eradicate pest, I decided to dig out the entire bed last weekend and perform a full soil exchange. First, I began by pulling out all the radishes, which were filled with larvae that was tunneling and destroying my food. As I began to look more closely, I realized these pests had no front legs, which wireworm has. Instead, they appeared to be radish maggot — yuck!

Tree Roots Throughout the Veggie Bed

Tree Roots Throughout the Veggie Bed

So, the good thing – no wireworm. The bad thing – a different pest that attacks tuberous crops like radish and turnip as well as brassicas like cabbage, cauliflower and broccoli. Plus, this larvae is laid by a tiny fly — something hard to keep off crops even when using floating row covers. They’re so tiny, they can slip through the fluttering cloth or even lay larvae in the soil near crops that the larvae will later attack.

Because this bed may have had a significant infestation and because of the tunnel mystery, I continued to dig, exposing yet another root of the problem — this time tree roots! Our neighbor’s lovely Sorbus had apparently sent out roots over the years — perhaps even before we installed our raised beds. And, those roots had found a source for life-sustaining summer water — our irrigated raised beds. The roots had growth throughout the bed, which answered why it seemed we could never irrigate this particular bed sufficiently. So, after I dug out a large portion of the bed, Bob cut back the roots, following them as far back as he could in our yard, away from the raised beds themselves.

Divided Bed After Roots Removed & Soil Exchanged

Divided Bed After Roots Removed & Soil Exchanged

Although the raised bed had been partially planted with radish and partially planted with beet, we decided to install a new cedar board in the middle of the box and only exchange the soil in 50% of the bed. We’re leaving the beets to grow. It may be a mistake, but for now, it doesn’t appear that the maggots have infested these. I’ll be watching them closely, and we may exchange the remainder of the soil later if the issue continues. As for the soil we removed, I’ve placed it on a tarp in the hot sun to, ideally, cook the livin’ daylights out of anything in it.

Now, as for the bed itself, it does have a crop rotation plan that began with last year’s crops and continues into the foreseeable future. Whether I can keep out a tiny fly or not is always a question. Whether I’ll put down materials at the base of each seedling to keep the fly from laying its egg near the base of each plant is also a question. With seedlings this is definitely an option; with sown seed crops like radish, I’m not so sure.  Have a good suggestion? Please let me know!


  1. We rotate everything in the vegetable garden every year. No problems so far. Sorry, I’ve no suggestions regarding your radish issue. Hope you can get to the bottom of it.

  2. […] This post was mentioned on Twitter by gardenmentor and Todd Inman, Todd. Todd said: Garden Coach Providing Free Garden Help | GardenHelp.org: Sure, it's fun to dabble with a veggie garden space. It … http://bit.ly/9WscNL […]

  3. rhaglund says:

    2 months later…we’re now harvesting beets from the side on which we did not exchange the soil. So far, they’re great! I did, however, notice that tree roots are heaving in the raised bed next door to this one – ugh! That bed’s full of blueberries & strawberries. More work ahead…

  4. Jerry says:

    The best way to control tree roots is to dig a trench between the garden and the tree. The trench should be at least 24″ deep so you cut the roots going to the garden. Do this near as far from the garden as possible to delay how long it takes for new roots to grow back. You could also install a sheet of plastic or roofing paper in the trench before refilling it to provide a partially effective root barrier.

  5. rhaglund says:

    Jerry, thanks for writing in. I don’t know that I agree with your methods, but thanks for sharing!

  6. […] vegetable beds. I disliked it for all the tenacious seedlings it gave me to pull. It frustrated me by sending strong roots into my vegetable beds, draining much needed moisture from my food crops. And, mostly, it made me sick when it bloomed […]

  7. […] vegetable beds. I disliked it for all the tenacious seedlings it gave me to pull. It frustrated me by sending strong roots into my vegetable beds, draining much needed moisture from my food crops. And, mostly, it made me sick when it bloomed […]

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