Question of the Week
Since mustards are a prime host, I will assume that brassicas, such as broccoli and cabbage are being attacked.
Harlequin bug (Murgantia histrionica), a member of the Stinkbug family
(illustration from http://ipm.ncsu.edu/AG295/html/harlequin_bug.htm)
This is a difficult pest to control due to its mobility and relatively wide host range. Ideally, several approaches based on the ecology of the stinkbug should be integrated to increase the environmental “pressure” on the pest. Harlequin bugs have evolved as crucifer-feeding specialists, so they have an affinity for plants in this family. Weedy hosts include wild mustard, shepherd's purse, peppergrass, bittercress, and watercress (1). Once the mustards become scarce, generally as a result of natural senescence, the bugs will move to squash, corn, beans, asparagus, okra, and tomatoes (1).
There are some possible weak links in its life cycle that might be taken advantage of. This pest will generally overwinter as an adult and then begin egg-laying a couple of weeks after it becomes active in the spring. In this context, it requires nitrogen for the egg-laying effort. Early-season crucifers, as they are forming seeds, are a good source of nitrogen at about the same time that the stinkbugs require nitrogen (2). It seems likely that if this nitrogen source were eliminated, harlequin bug egg production and egg viability would decrease. In California, one suggested strategy is to replace wild radish and crucifer populations that grow along roadsides and fields with native grasses. Native grasses are not attractive to stink bugs; they do not form their seeds until later in the growing season and are thus poor sources of nitrogen. Trap crops of flowering mustards have been suggested to manage harlequin bug populations. The obvious problem with this technique is finding effective and inexpensive ways to destroy the stinkbugs coming to the trap crop in a timely fashion so that they will not infest the actual brassica crop.
Another option is to increase predation of the harlequin bug. Recent research in California has found, surprisingly, that the “roly poly"—also known as the “pill bug,” due to its tendency to roll up into a pill-sized ball when disturbed—is an effective predator of harlequin bug eggs. Previously, it was thought that pill bugs fed only on decaying vegetation, but it turns out that they are nocturnal predators, climbing into plants at night in search of harlequin bug eggs and other stinkbug-family eggs. Mulching your crops with hay or woodchips may provide habitat for ground beetles and spiders that would feed on the eggs and stinkbug nymphs. Since mulching may provide overwintering sites for the stinkbug, the mulch should be removed or incorporated into the soil after the crop is harvested.
Increased predation should be accompanied by destruction of overwintering sites for the harlequin bug. Plant debris and leaf litter should be destroyed. However, it should be noted that this may be the same kind of habitat required by the predatory pill bug that feeds on stinkbug eggs. Your observations about where the harlequin stinkbugs are overwintering on your farm will guide future management efforts.
The varieties listed in the table below have some resistance to stinkbug damage and have been recommended by North Carolina State University for planting (1). Please keep in mind that the different conditions in your location relative to North Carolina may influence the plant’s development and its level of resistance.
Copenhagen Market 86, Headstart, Savoy Perfection Drumhead, Stein's Flat Dutch, and Early Jersey Wakefield
Green Glaze, Georgia (3)
Early Snowball X, Snowball Y
Red Devil, White Icicle, Cherry Belle, Champion, Red Prince, Globemaster
Row covers may be used to cover the brassicas and physically protect the plants from harlequin bug feeding, but must be placed before egg laying starts.
Liquid formulations of pyrethrum, sabadilla, and rotenone are organically acceptable botanical insecticides that are effective against the harlequin bug, but they can also harm beneficial insects.
Finally, you may wish to experiment with the particle film barrier Surround™, a processed formulation of kaolin clay. Registered for use on brassicas and most other vegetable crops, it has proved effective against leafhoppers and sharpshooters, and may have some efficacy against stinkbugs. It may act to deter feeding and egg-laying behavior once the insect has landed on the plant, as well as disguise the plant from being discovered in the first place. It is probably best for early season use, as the particle film would be difficult to wash off if applied before harvest. Contact John Mosko (see below) for additional information or material for variety trials.
101 Wood Avenue
P.O. Box 770
Iselin, NJ 08830-0770
Dufour, R. 2000. Farmscaping to enhance biological control. ATTRA publication. 39 p.
1. North Carolina State University IPM Web page. INSECT and related PESTS of VEGETABLES, Harlequin Stink Bug. http://ipm.ncsu.edu/AG295/html/harlequin_bug.htm
2. Ehler, L. 2000. Farmscape Ecology of Stinkbugs in Northern California. Entomological Society of America.
3. Harris, P., Jarratt, J.H., Killebrew, F., Byrd, Jr., J.D., and R. Snyder. Publication 2036. Mississipi State University Extension Service. http://msucares.com/pubs/publications/p2036.htm
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