Swede Midge Fly Management

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 non-toxic solutions.

Protect 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.

Swede midge is a pest in many parts of the northeastern United States, including New York, Vermont, and New Hampshire. It has also been found in Minnesota, Illinois, and Wisconsin. 

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.

Recommendations for 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 new growing seasons.

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.

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

   • Grow regular spinach which must be started from seed. Best to plant the seeds in November.

   • Grow Red Malabar Spinach from seed indoors to give it a head start. This leafy green veggie doesn’t look like normal spinach, but has a similar taste. Unlike normal spinach, it grows well through the warm summer season. Plant it when you plant summer crops like tomatoes. It’s a vine that winds around any structure, trellis or plant nearby. Give it a big tall trellis.

   • 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.

   • Beet greens look and taste like Swiss Chard. Direct sow the seeds in spring

   • Other veggies to try are:

     • Lettuce (various types, including romaine, butterhead, and iceberg)

     • Fresh herbs (cilantro, dill, parsley, chives, etc.)

     • Green onion

     • Leek

     • Chicory, Endive, Escarole, Radicchio

     • Fennel

     • French Tarragon

     • Asparagus

     • Celery

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.

• 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 about harvesting collard greens and protecting them with large 4 x 4 foot netting bags supported by garden stakes. Their system protects from cabbage worms and butterflies, since they haven’t yet been invaded by Swede Midge.
  -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 stones, wood or garden staples to hold down the bottom of netting against the soil.
  -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 or hoops made of bendable white PVC half-inch pipes, see our blog post Installing Hoops on Raised Beds.

• 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. Put 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) and see our blog post Installing Hoops on Raised Beds.

• 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

Order Bug Netting and Bags from Deep Roots

You can order bug netting and bags from Deep Roots. We have not yet added an online store page for netting. To order call, text or email our customer support team – support[at]deep-roots-project.org AND 708-655-5299.

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.

(708) 655-5299 and support[at]deep-roots-project.org

Please leave your cell phone number when you sign up for our eNewsletter, if you want text message announcements now and then. 

Donations help us provide organic kitchen gardening education to individuals, organizations, and entire communities. Thank you in advance for contributing to our community and for sharing our website and blog with friends and family.