Grace Hensley
July 21, 2014

When Susy Morris, who blogs and farms in Liberty, Maine, went out to her vegetable garden in early June, she spotted a few different kinds of beetles on her asparagus, cucumbers and potatoes, but the harlequin bugs that attacked her cabbages were making a holey mess of her garden.

Harlequin bugs (Murgantia histronica) are red or yellow and black hard-shelled bugs in the stink bug family. Found in warm southern states as early as the Civil War, harlequin bug territory can now reach as far north as the Great Lakes and New England. Fortunately, I’m blessed by the cool maritime climate in the Pacific Northwest and don’t encounter them—you can hate me if you want.

Adult harlequin bugs overwinter in old plants, then lay eggs in the spring. Looking like some kind of Mod furniture, the barrel-shaped striped egg cases are quite distinctive. These insect pests can reach adult stage in an alarmingly short 48 days, so when you find the eggs, be vigilant in destroying them.

harlequin bugs
Ken-ichi Ueda/Flickr

Insect pests are often named for the host plant that they consume, so harlequin bugs ought to be named broccoli bug or cabbage bug. They feast on all members of the brassica family, including collardskale and even related ornamental genuses, such as Cleome, Matthiola, Erysimum (wall flowers) and Alyssum. A bit like vampires, harlequin bugs pierce stems and leaves and suck out plant juices, so look for discolored spots around a hole in your leaves.

Unfortunately, these sap-sucking insects will also eat tomatoes, corn, beans, squashokra and tree fruits, so take the time to inspect any plants that are wilting. Because males produce an attracting pheromone, the bugs tend to congregate in one place, so look for unusually stressed plants in otherwise healthy rows.

Below are twelve organic techniques that will keep your kale and broccoli free from harlequin bug destruction.

General Techniques

Standard pest-management strategies will help you deal with pests of all types, including harlequin bugs. Here are a few you should incorporate into your garden-maintenance plan.

1. Encourage Strong Plants

Pay attention to your crops’ water and soil needs. Water deeply to encourage strong, deep roots. Brassicas are heavy calcium feeders, so add ground oyster shells or eggshells when you plant. You might need to add dolomitic limestone make calcium more available to your plants. Soil tests are also important for new crop fields and will tell you how to better balance out your soil’s nutrients.

2. Weed and Clean

Promptly remove languishing plants from the garden and inspect them for pests. (If they are infested, throw them in the trash, not the compost.) In mid-summer and again in the fall, pick up leaf-litter and remove weedy habitat, where the adult harlequin bugs can overwinter.

3. Hand-Pick Bugs

Toss harlequin bugs in a bucket of soapy water; squishing them will emit a pungent odor. (They aren’t called stink bugs for nothing!) Be vigilant in this practice, especially in spring as the weather warms.

Physical Deterrents

If you have a large garden plot where hand-picking pests is unreasonable, barrier methods can be effective in keeping pests like harlequin bugs at bay.

4. Row Covers

Row covers, which are suspended above the crop on PVC piping or wire, work really well for plants, like cabbage, that don’t need pollination to produce—they can stay under their fleece from planting until harvest. Use a lightweight, pervious fabric, such as Reemay, and tuck in the fabric edges with stones or soil to prevent harlequin bugs and other pests from slipping in underneath.

5. Kaolin Clay

Typically used on fruit crops, this white silicate clay can be sprayed to prevent bugs from feeding and is easily washed off at harvest.

Organic Chemical Solutions

While pesticides—even organic ones—shouldn’t be the first pest-management solution you turn to, they can be used sparingly if you have an infestation or if your site is too large to manage by other means.

6. Insecticidal Soaps

An effective way to kill harlequin bugs is with a simple combination of a 1-percent insecticidal soap solution, which penetrates their hard shells, and neem (0.9 percent) or pyrethrin (0.012 percent). This combination is a contact-insecticide, so you’ll have to squirt the eggs, nymphs and adults directly. Apply insecticidal soaps in early morning, before the bugs are active, to maximize effectiveness. Do not use neonicotinoid insecticides, as there is increasing evidence that it is a widespread bee killer.

7. Home-Brewed Pesticides

Plant Chrysanthemum cinerariifolium (also known as Tanacetum cinerarifolium), a white daisy-like plant that will deter all pests naturally by attacking the nervous system of insects. Commercially available as pyrethrins, this chemical is derived from the seeds of this plant. Collect flower heads when they are in full bloom. Dry and grind them up. Soak 1 cup of powder in 1/2 gallon of very warm water for 3 hours. Add 1/2 cup of dish soap and use immediately. Repeat weekly as nymphs hatch.

Companion Plants and Polycultures

These age-old strategies might have been used by your grandma, but they’re reliable strategies that can be used for managing all kinds of pests.

8. Boundary Crop

Surround brassicas with strong-scented plants, such as chamomile, celery, basil, garlic, mint, rosemary and sage, to help mask their strong odors. You can even plant chrysanthemum, a natural pyrethrin producer.

9. Trap Crops

Grow an early crop of mustard, broccoli or kale to attract and trap pests. Harvest and discard this crop before your main crop is planted.

10. Polycultures/Intercropping

Instead of growing them as a boundary, inter-mix main crop with the plants listed in No. 8 to distract harlequin bugs.

Animal Help

Greatly reduce your workload by using predatory insects and animals that feast upon harlequin bugs to rid your garden of this pest.

11. Parasitoid Wasps

Effective against hard-shelled pests, tiny non-stinging hymenopteran wasps are tireless workers. You can order these wasps online or plant wildflowers and herbs with broad umbrella-like blooms, such as yarrow, caraway and fennel to encourage them into your garden. Don’t purchase braconid and trichogramman wasps for use against harlequin bugs, though—they prefer the soft-bodied aphids, cutworms, moths and caterpillars.

12. Guinea Fowl

Of all the methods mentioned, I like this solution from Morris best. She lets her small flock of guinea fowl free-range her garden during the day. Although slightly noisier than chickens, a small flock is a useful companion in the field, as they are much less destructive to leafy crops and don’t scratch up plants as aggressively as chickens.

Next Up