Harlequin Bugs – A Growing Problem in Pennsylvania?
Penn State Extension entomologist Shelby Fleischer and colleagues would like to learn from growers if it and other related true bug species are a problem in your fields.
This pest has the ability to destroy the entire crop where it is not controlled.
The harlequin bug injures the host plants by injecting salivary secretions that liquefy plant tissue which they then ingest, causing the plants to wilt, brown and die. Plants commonly attacked by the harlequin bug include such crucifers as cabbage, cauliflower, collards, mustard, Brussels sprouts, turnip, kohlrabi and radish. Two growers recently reported harlequin bugs rendering kale unmarketable without control. In the absence of these favorite hosts, tomato, potato, eggplant, okra, bean, asparagus, beet, weeds, fruit trees and field crops may be eaten.
In northern climates like Pennsylvania, only adult harlequin bugs can survive the winter. They will emerge from hiding places such as crop residue during the first warm days of spring.
To control harlequin bugs, start with cultural controls. Host-free periods without brassicas can help limit the population. Remember brassica cover crops, like forage radish, are known hosts. Harlequin can also feed and reproduce on wild weedy mustards (Shepherd’s purse, wild mustard, pepperweed), pigweed (Amaranthus spp.), lambsquarter (Chenopodium spp.). Keeping these weeds under control in fields and on field edges will limit habitat. Leftover crop residue in the field provides a protected host area for over-wintering adult harlequins. Remove or disk in residue to destroy overwintering sites. Trap crops have been recommended, but I would suggest that you need to rapidly kill the bugs in the trap crop, or destroy the trap crop and follow it with a host-free period, for this to work well. Plant an early crop of horseradish, mustard or kale and try to kill the harlequin bugs concentrated on this favorite host. One grower has successfully controlled harlequin by frequent vacuuming.
Insecticide controls include pyrethroids and/or neonicotinoids. See the Commercial Vegetable Production Recommendations guide for insecticide options. Pyrethrins are allowable in organic production. According to Dr. Fleischer, starting early in the season with up to three applications within a two week window at the highest labeled rate and continuing until the problem is gone is likely to control harlequin. However, he notes this option would be expensive and labor intensive.
Reports in Pennsylvania tend to be on organic farms. This may be due to fewer brassica-free periods, smaller plot size or other factors.