Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu
By now everyone has heard about the brown marmorated stink bug (BMSB) Halyomorpha halys that was accidentally introduced into the United States in shipping containers arriving from Asia. The first confirmed specimen was collected in Allentown, PA in October 2001, although there is evidence that it was collected from black light traps in New Jersey as early as 2000. Since becoming established in Pennsylvania, the BMSB has spread throughout the Mid-Atlantic as far south as Virginia. It also has been found in several southern and Midwestern states.
The BMSB more than likely has a single generation per year in Maryland. Adults emerge from overwintering sites during late May through the beginning of June. They mate and lay eggs from June through August and probably into September. The eggs hatch into small black and red nymphs that go through five molts throughout July and August. Adults begin to show in mid-August. Their flights for overwintering sites start in mid-September and continue through October.
If you look at web sites that discuss BMSBs many maintain that it is just a nuisance pest and mostly to home owners, but not to commercial fruit or vegetable growers. That has all changed this year. Fruits such as apple, peach, and raspberries have been attacked in western and to a lesser degree in north central Maryland. When BMSBs feed on apple they cause cat facing as well as deformation and internal brown spotting of peaches rendering all of the fruit unmarketable for fresh market. It also has been found feeding on sweet and field corn (where there is no kernel development), tomato (where there is fruit distortion and cloudy spot), pepper (fruit distortion and cloudy spot), and to a lesser degree on okra and sunflower in central and southern Maryland (Fig. 1). The damage from BMSB feeding is especially bad on some vegetables where it can deform the fruit more severely than other stink bug species (Fig. 1). Whether this is due to greater amounts or different types of enzymes in its saliva is not known. The BMSB also seems to more readily introduce yeast contaminants into its feeding sites that further degrade the fruit. I have found some populations of BMSB in almost every vegetable field I have looked at over the last few weeks. In most cases the pest is doing some damage, but not a great deal. The worst vegetables for damage appear to be tomato and pepper.
In Delaware, we have found BMSB feeding on tomatoes, peppers, okra, sweet corn and field corn in New Castle County but we have not seen it or heard report of damage to vegetable crops in Kent and Sussex County. It should be noted that we have also found it in soybeans fields for the first time in New Castle County and just this week in Kent County (comments from Joanne Whalen, University of Delaware).
I do not know if BMSB populations will continue at these extraordinarily high levels in the next couple of years. We had a “perfect storm” develop this summer for the Brown marmorated population to explode. We had a severe drought early in the summer along with extreme heat. These two factors literally dried up the usual wild plant hosts of not only BMSB but other pests as well and drove them into our fruit and vegetable fields. The dry weather appeared to be conducive to BMSB survival as their population exploded in August. We probably will not have these same conditions next year and will most likely not see these high populations again–hopefully. However, we just don’t know enough to predict accurately what the situation will be in the coming years. I, like many others, will be conducting studies next year to see if we can find some consistent strategies for their control (this will include organic treatments too). This pest is something we should be watching for in our vegetable fields and taking note of, but it should not cause panic.
Figure 1. Brown marmorated stink bug nymph (upper) and adult (lower)
Figure 2. Damage to various vegetables by Brown marmorated stink bug