Efficacy of select insecticide seed treatments and in-furrow applications for managing the brown stink bug, Euschistus servus (Say) (Hemiptera: Pentatomidae), in seedling maize
Introduction
The brown stink bug, Euschistus servus (Say), is an increasingly common early season pest of maize (commonly referred to as “corn” or “field corn”), Zea mays L., in the southeastern United States. Euchistus servus pest populations may be increasing due to a variety of factors, including decreased use of broad spectrum insecticides in other crops and shifting farm management practices favoring large overwintering populations, such as reduced tillage (McPherson and McPherson 2000; Greene et al., 2001; Annan and Bergman 1988).
Seedling maize is susceptible to injury and subsequent yield reduction when fed upon by E. servus (Townsend and Sedlacek 1986; Annan and Bergman 1988; Sedlacek and Townsend 1988; Apriyanto et al. 1989a, 1989b). Stink bug feeding can delay maturity, cause growth deformities (tillering), and decrease mean extended leaf height and mean grain weight per ear (Apriyanto et al., 1989a). Injury from stink bug feeding increases with the insect density and duration of infestation; however, yield can be reduced by a single day of feeding (Annan and Bergman 1988; Sedlacek and Townsend 1988; Apriyanto et al., 1989b). The most susceptible stages of maize development to stink bug injury are VE (emergence) through V2, and susceptibility decreases through V6. Beyond this point no yield impact likely occurs until the last vegetative stages prior to tassel (Sedlacek and Townsend 1988, Annan and Bergman, 2018).
Plant injury as a result of E. servus feeding often develops several weeks after feeding occurs and scouting for stink bug pests is complicated by their mobility and low visibility in crop residues. Thus, in some high-risk scenarios, preventative measures may be needed to effectively mitigate injury. Insecticides used currently on seeds and or insecticides that are applied during planting to target other pests, may additionally control E. servus without unnecessarily increasing current production costs or environmental residues. Neonicotinoid insecticides, namely clothianidin and thiamethoxam, are applied to almost all commercially-available corn seed (Douglas and Tooker 2015). Neonicotinoids are detectable in plant roots, stems, and leaves for up to 47 days after planting when applied at the maximum commercially available rate (1.25 mg A.I./seed) (Alford and Krupke 2017), which can span the susceptible window for stink bug injury when conditions are favorable to crop growth. The amount of insecticide in plant tissue is likely not sufficient to provide control for this entire window.
Organophosphate insecticides (e.g., terbufos and dicrotophos) can be applied in the seed furrow at planting to control some below ground pests as well as foliar applications for stink bugs (Flessner and Cahoon 2020). Pyrethroid insecticides (e.g., bifenthrin, lambda-cyhalothrin) are similarly used and are also labeled for foliar management of E. servus in corn (Flessner and Cahoon 2020). Although organophosphates and pyrethroids are targeting below ground pests when applied in the seed-furrow, E. servus could potentially encounter toxic residues in or on top of the soil due to their feeding behavior at or just below the soil surface.
Seed-applied and or in-furrow insecticide applications may provide protection for plants until they mature out of the critical period for E. servus injury. Pyrethroids, organophosphates, and neonicotinoids have all been shown to cause mortality in stink bugs in different cropping systems and using different application methods (Reisig 2011; Kuhar et al., 2012; Little 2014). Our current study seeks to assess the impact of E. servus feeding on maize in the presence of various early season insecticides. The impact on early plant growth and injury, the effects on stink bug feeding and mortality, and grain yield were assessed.
Section snippets
Insects
Procedures for rearing field collected insects were described in Bryant et al., (2020). In short, brown stink bugs were collected from wheat and corn and stored in environmental chambers with green beans and sterilized water for up to one week prior to use in the field experiments described here.
Field experiments
Experiments were conducted in 2018 and 2019 at the Tidewater Agricultural Research and Extension Center in Suffolk, Virginia, USA to determine if insecticides applied at planting provide early-season
E. servus feeding and mortality
In 2018, there was a relationship between insecticide treatment and the number E. servus feeding on plants (X2 = 26.97; df = 3; p < 0.001), and a relationship between insecticide treatment and the number of E. servus mortalities (X2 = 27.05; df = 3; p < 0.001). The number observed feeding on plants and mortality was highest in the highest rate of clothianidin combined with bifenthrin compared to all other treatments.
In early planted maize in 2019, there was no relationship between the
Discussion
The results of this study indicate that clothianidin, that are applied to almost all commercially available seed, have the potential to prevent severe (i.e. stunting, multiple tillers, excessive leaf injury) early season injury from E. servus feeding. Our results also suggest that earlier planted corn may be less susceptible to long term injury and yield reduction as a result of stink bug feeding, although further study is needed to confirm these results. Results also demonstrated that
Conclusions
The brown stink bug, Euschistus servus, is an increasingly important pest of maize in the southeastern United States. Due to the nature of feeding in early growth stages, injury is often not observed until it is too late to mitigate. Our study examined preventative treatments that are ubiquitously applied, to assess their efficacy for brown stink bug management. Results suggest that systemic seed treatments of clothianidin mitigated or eliminated the impact of early feeding on plant injury,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We would like to thank Dr. Adam Alford and Dr. Sean Malone for providing edits on this manuscript as well technical support in conducting experiments. We would also like to thank the Virginia Grain Producers associated for partial funding in completing this work. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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