Suburban organic gardeners in Illinois usually protect their Brassica crops (kale, collards, cabbage, etc.) from cabbage moths and their caterpillars. But, brace yourselves for a new Brassica family pest challenge – the tiny Swede Midge fly. There are conventional toxic pesticide sprays that do control and prevent swede midge that we can’t use in our organic gardens. Deep Roots consulted with the Chicago Botanic Garden Plant Information Service about the best solution.

Protect Your Collards, Kale & Cabbage from Pests

The swede midge fly (Contarinia nasturtii), an invasive pest from Europe, has begun wreaking havoc on brassica crops. including radish, horseradish, rutabaga, turnip, rapeseed (canola), arugula, bok choy and Chinese cabbage. Crops that are most damaged include common favorites such as broccoli, cauliflower, cabbage, kale, kohlrabi, collards and Brussels sprouts.

Swede midge are very tiny lightweight flies that can spread long distances by the wind. Their life cycle is between May to October in Zones 5 and 6 (Chicagoland area). The first year or so of its presence often goes unnoticed, but un-recognized populations can quickly build up and devastate brassica crops. There are conventional toxic pesticide sprays that do control and prevent swede midge that we can’t use in our organic gardens.

Understanding the swede midge life cycle is helpful

We expect the swede middle will find our collards kale and cabbage. Once the damage is visible there is no way to save the plant. Cut down the plant stem at the soil and put in the garbage – not the compost bin.

The fly’s life cycle repeats about 5 times every growing season. Adult flies live for a few days, just long enough to reproduce and lay 2 to 50 eggs on the newest growth points of a Brassica host plant. The emerging larvae (maggots) feed by secreting digestive enzymes, damaging the plant’s growing points and causing deformities or preventing proper head formation.

After the maggots are well fed and fully grown, they dive into the top inch of soil to pupate – transform back into a fly. They emerge from the soil as adult flies within a week or two, depending upon soil temperature and moisture, and start the cycle over again. But if buried below 2 inches, the pupae can survive for two years and can emerge if digging or tilling brings them higher up at a later time.

Identifying swede midge damage

In the worst cases, damage to single-stemmed heading brassica crops such as broccoli, cauliflower and cabbage looks as if the plants have been pinched back, preventing a single large head from forming. Because feeding damage can vary greatly depending on where the larvae feed on the plant and on the stage of plant development, it can be confused with many other issues.

Eat the unaffected collard, kale and cabbage leaves

This method has been approved by the Chicago Botanical Garden Plant Information Service (847-835-0972). If a collard, kale and cabbage plant is infested with swede midge, you might still consider eating the unaffected leaves, but it's essential to take a few precautions. Make sure the leaves are thoroughly cleaned and cooked to minimize any potential risks associated with the infestation. Here are some steps to consider if you want to eat the unaffected leaves:

1. Inspect the whole plant: Carefully cut off any infected stems or parts.

2. Inspect the leaves: Carefully check the leaves for any signs of damage or presence of larvae. The larvae are very small and might not be immediately visible to the naked eye.

3. Wash thoroughly: Even if some leaves appear unaffected, wash them thoroughly in water, possibly with a mild soap solution, to remove any larvae or eggs that might be present.

4. Cook the leaves: Cooking can help ensure that any remaining insects or pathogens are killed. It's generally safer to eat cooked leaves than raw, especially if there's a chance they've been exposed to pests.

5. Monitor the plant: Keep an eye on the plant for further signs of infestation. If the infestation is severe, it might be better to remove and destroy the affected plant to prevent the pests from spreading.

6. Remove a plant without pulling the root in order to keep the healthy soil microbes in the soil. Not disturbing the soil as much as possible is a basic principle of our regenerative gardening method. Pull out the roots of only root crops like beets.

Our recommendations to successful organic food harvest

Until agricultural scientists find an effective and simple way to organically and safely prevent or control swede midge. You won’t know if swede midge has already infected your soil before you plant. Deep Roots have suggestions for the 2024 growing season.

1. Protect a few collards, kale and cabbage plants with bug netting. See below details for a few options and links to videos.

2. It’s risky to buy seedlings from a garden center since they could be already infected by swede midge. Only buy them if they have been stored indoors.  Deep Roots is growing collards from seed indoors and can share some  seedlings.

3. DON’T grow brassica crops this year. Substitute other leafy greens and veggies. Two suggestions

   -Deep Roots is growing Red Malabar Spinach from seed to share with local gardeners.This leafy green veggie looks and tastes similar to spinach, but grows well through the warm summer season.
   -Buy Swiss Chard seedlings at garden centers. It grows through spring and summer. Eat the leaves and the stems. We usually add the leaves to a salad and make hummus from the stems.

Make physical barriers with bug netting:

You won’t know until you try to grow Brassicas if your soil is already infected. If your soil is NOT already infected, physical barriers are a crucial defense mechanism. Cover your brassica plants with fine insect netting throughout the growing season. Place small groups of Brassica family crops under bug netting bags, or cover your whole bed with bug netting.

Deep Roots Project keeps a large supply of bug netting sheets and bags. We will sell them from our online store. Contact support[at]deep-roots-project.org.

• Bug netting bags protect small groups of plants in a raised bed: Bags can be different heights. Learn more details in this video: Growing Georgia Southern Collards Greens
  -Tall brassicas (like kale, collards): Since these plants can grow 4 to 5 feet tall, use larger bug netting bags designed for big fruiting plants. Support the netting with 2-3 wooden stakes inside the bag to prevent it from resting on the plants and potentially damaging them. Use garden staples to hold down the bottom of netting.
  -Short Brassicas (like cabbage): Use smaller bug netting bags suitable for their height. Or place sheets of bug netting on the plants supported by sticks,

• Bug netting on a cloth grow bag: Plant 2-3 collard plants in a cloth grow bag. Support the netting with a wooden stake or a wire hoop placed inside the bag to prevent it from resting on the plants. But something soft at the top the stake so it doesn’t poke a hole in the netting,

• Bug netting supported by hoops: Cover your entire bed with a sheet of fine bug netting supported by hoops. You can use various materials for the hoops. The hoops can be pushed into the soil or attached to the raised bed frame. Learn more details in this video: How to Make Hoops for Raised Beds (4 Ways)

• Bug netting attached to a hinged hoop house: Another option is to hinge a wooden rectangle to the top of your raised bed. Attach the hoops to the rectangle. Learn more details in this video: How to Build a Hinged Hoop House

Other Brassica Family Pests

Please see our Brassica Family Pests and Diseases post for information about other Brassica family pests.

“Grow Your Own Food” blog posts

See the full list of our Grow Your Own Food blog posts. Each post is assigned ”tags” which are under the post title. If you need a quick answer to a gardening question give us a call or send a text to our customer support team – support[at]deep-roots-project.org AND 708-655-5299.

Deep Roots online store

See our online store for details about prices, ordering and delivery of raised beds, planter boxes, microbe-rich compost, worm castings, leaf mulch and more. We don’t sell traditional soil, since we use 100% compost as our growing medium. Our online store has 2 sections – (1) raised beds and planter boxes and (2) compost, worm castings, fertilizer.

Please contact our customer support team before placing an order online so we can assist you with the details and answer your gardening questions. You can pay by credit card in the store or by check.

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