Have you have ever grown any kind of Brassica crop? Did you encounter a gaudy black and orange bug that is shaped like a stink bug on your broccoli or cauliflower plants? If so, this was the Harlequin bug, and it is a major pest of Brassica crops in the southern United States. It is not normally a problem north of a line drawn across the country at the approximate height of Pennsylvania and Colorado. Unfortunately, it is a problem that growers in more northern regions of its range are seeing more of lately.
Harlequin bugs are capable of killing a Brassica crop if left unchecked. They are not picky and will feed on broccoli, cabbage, cauliflower, brussel sprouts, kale, collards, mustards, turnips, horseradish radishes, etc. Once they finish demolishing your Brassicas, they can also migrate onto other crops such as tomatoes, peppers, asparagus, beans, potatoes, fruit trees, field crops. They can feed on most anything desirable you might be growing to eat.
Harlequin bugs don’t truly hibernate. This means that they can and will be active as soon as you plant out your earliest crops. However, in our experience, they can be a particularly large problem on heat stressed cold crops—both later on in the spring and in the early fall.
They are sap sucking insects. They spend their whole lives starting from the time they hatch sucking the sap out of your plant’s leaves. Not only are they sucking your plant’s precious ‘blood’ but they are also damaging the leaf tissue with their feeding activities leaving brown spots. The combination of sap sucking and leaf damage can result in the entire plant eventually browning, wilting and dying.
Recognizing these destructive pests
The good news is that Harlequin bugs are gaudy at all life stages. They are not good at camouflage. They hatch out of very distinct looking black and white striped egg clusters. These clusters are typically found on the backs of leaves. If you find egg clusters, remove and destroy them!
These eggs hatch out into very small round bugs called nymphs. They go through 5 or 6 nymph stages over the course of 1-2 months before becoming mature adults capable of mating. Each nymph stage is larger and slightly different looking. They start out small with very little orange on them, but get larger and more orange at each phase. Nymph pictures are scattered throughout this article. Plus University of Florida has additional pictures of some nymph stages.
How do we control them?
To begin with there are a couple cultural practices that you should use to help keep down their numbers, and to prevent them from overwintering in your garden. Before you implement any of the following techniques, it is important to make sure that you are controlling all the wild mustard type weeds that Harlequin bugs like to feed on. If you are not controlling the weeds in and around your garden other cultural control methods will not be as effective.
If you have low numbers of Harlequin bugs present, handpicking them can provide sufficient control. This is particularly true if you pick and destroy the adults in the spring and fall as they are going into/emerging from hibernation. Killing as many overwintering adults as possible reduces the number that will be present to lay eggs in the spring.
What if there are too many to hand pick?
Another technique that you can use if you have large numbers of the present is planting a trap crop. Plant a mustard crop very early in the season, once the bugs have all migrated over to the trap crop you can spray, burn or otherwise destroy them on the trap plants. Then you can plant your actual crop after you have destroyed a large percentage of the overwintered adults.
Perhaps most importantly
Probably one of the most important cultural control methods is to destroy all crop residue in the fall after your crops are harvested. This way the bugs will not be able to overwinter on the crop residues. Additionally, if you live somewhere that the season is long enough to grow both a spring and a fall Brassica crop, it is a good idea to destroy all crop residue after harvesting your spring crops.
Do not allow any heat stressed Brassicas to remain in your garden during the summer. They will breed Harlequin bugs like crazy. Instead remove all of them and allow your garden to go a couple months devoid of anything in the Brassica family so that the bugs migrate elsewhere. Once your garden has been devoid of Brassicas for a few months, the Harlequin bugs should have moved on. Then you can plant your fall crop.
Because adult Harlequin bugs will overwinter in your garden it can be tricky to eliminate them completely. However, using the above techniques combined with insect barrier should keep their numbers very low. The same insect barrier used to protect your crops from cabbage worms should prevent Harlequin bug problems as well. Since adults overwinter on debris in your garden, check underneath your insect barrier periodically to make sure you don’t have any pests that hatched out underneath it.
Chemical methods of control
A combination of the above methods will likely be enough to control Harlequin bug populations for most homeowners. We would encourage you to try growing all your Brassica family crops under row covers before resorting to pesticides. Row covers can save you a lot of time and frustration.
If row covers and cultural practices are not to be enough to prevent Harlequin bug damage, there are a variety of common pesticides labeled for killing Harlequin bugs. Pyrethroid and carbaryl are examples of some pesticides commonly used for Harlequin bugs. Be sure to check with a local extension agent if you have any questions about using pesticides. Also be sure to read and follow all label directions carefully.
Next time you see a beautiful black and orange bug crawling around in your garden, admire its beauty, and then squish it before it has a chance to destroy your hard worked for crops.
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