During the last two weeks of April, I observed brown stink bugs (Euschistus spp.) (Figure 1) and green stink bugs (Nezara viridula) while scouting for aphids in wheat, but surprisingly I had not seen a single rice stink bug (Oebalus pugnax), ususally a very abundant species in wheat (Figure 2). Boxelder bugs (Boisea trivittata) (Figure 3) were observed in these wheat fields.
The numbers of stink bugs were not high (between 1 to 6) in three different fields nor the boxelder bugs. In addition, in western Kentucky we have seen a geographical spread of the brown marmorated stink bug (BMSB) (Halyomorpha halys) since 2020. Starting in the first days of April, BMSB were observed walking indoors in human dwellings or window screens coming out of their overwintering stage.
These stink bugs will feed and then mate, and a new generation of stink bugs will begin colonizing fruit, vegetables, corn, soybeans, and other crops. The first peak population occurs from mid-June to end of July, and the overwinter population that feeds on maturing pods or kernels occurs in mid-September to October.
This may be a personal perception after a hiatus from the COVID-19 pandemic, however, compared to previous years the presence of the brown, and green stink bug in wheat seems early. Also, reports of BMSB observed in houses may imply the potential for an outbreak of the first-generation stink bugs during this coming season for field crops. Thus, feeding and damage to seedling corn and soybeans may occur.
Likewise, boxelder bugs a common pest of dwellings were seen in large numbers in the fall of 2021 in Minnesota and outbreaks occurred in March and April in 2022. In wheat, boxelder bugs do not cause any damage but contribute to the perception that a potential stink bug outbreak may happen as green, brown, and BMSB were very abundant in central and western Kentucky in 2021.
In the spring and fall seasons of 2021 in western and central KY, farmers, and county extension agents observed large populations of stink bugs. Furthermore, the entomology team of the UK-REC at Princeton provided numerical data from several counties and reported changes in species composition numbers between 2020 and 2021.
Stink Bug Damage to Corn and Soybean Seedlings
In corn, adult and nymph stink bugs feed on seedlings. The result of this feeding causes oblong holes with yellow margins in the leaves as they emerge from the whorl, as well as twisting of the whorl. If heavy feeding occurs, it can cause death of the growing point. In soybeans adult and immature stages feed on tender tissue.
AgFax Weed Solutions
When stink bugs inject their digestive enzymes, they may cause delayed maturity and deformed leaf growth. In corn and soybeans, the most important damages occurs during the reproductive stage of plants affecting kernels and pods, that can cause abortion of seeds, reduce yields, and affect seed quality.
There are established thresholds for the number of stink bugs in corn and soybeans. There are several species in these crops, including the green stink bug (the most abundant), followed by BMSB, and the brown stink bug complex. Thus, tallies should include the mix of all adults and 3rd-4th instar nymphs of all these species to reach the thresholds for the different growth stages of corn or soybeans (Table 1).
Note that little information is available on damage in field corn and soybeans caused by BMSB, however, the thresholds shown in Table 1 may be used for these crops in this coming season independently of the species composition. If thresholds are met, judicious use of conventional insecticides registered for stink bugs may be used.