Hilling as a cultural control strategy for soybean gall midge (Diptera: Cecidomyiidae).

Soybean gall midge, Resseliella maxima Gagné, was recently identified as a new species causing significant injury to soybean and is currently found in 164 counties across 7 midwestern states (NE, IA, SD, MN, MO, ND, and KS). Infestation of soybean begins in late spring, when adults emerge from last year's soybean field. Infestation of a new soybean crop depends on the presence of fissures which start to form at the base of the soybean plant around the V2 stage. Field observations indicate that these fissures are only present below the cotyledonary nodes or in the area within 3-5 cm above the soil surface. To determine the importance of these fissures for R. maxima infestation and plant injury, hilling or the movement of the soil to cover the base of soybean plants at the V2-V3 stage was compared with the standard practice (no-hilling). Field studies were conducted at 3 sites in east-central Nebraska during the 2021 growing season. The results showed a significant reduction in the frequency of infested plants, larval number per plant, and plant injury for hilled compared to no-hill treatment. This reduction in the presence of larvae and plant injury corresponded with a significantly greater yield for hilled compared to the no-hill treatment. These results highlight the importance of fissures on soybean for R. maxima adult infestation as well as the potential for hilling to be used as a management strategy for R. maxima.

Evaluating the impact of at-plant termination of a cereal rye cover crop with different corn planting dates on arthropod activity.

Greater cover crop biomass is expected to result in a favorable microhabitat for beneficial arthropods. Natural Resources Conservation Service (NRCS) cover crop termination guidelines are based on the cash crop planting date. Therefore, a delay in cash crop planting could result in greater cover crop biomass. However, studies on delays in cash crop planting and greater cover crop biomass have led to a decrease in cash crop yield. Thus, a field study was conducted in eastern Nebraska over two years to evaluate the impact of early and late corn planting dates with at-plant cover crop terminations on pest potential, beneficial arthropod activity, and agronomic parameters. To measure arthropod activity and pests in the system, pitfall traps, and corn injury assessments were performed during the early stages of corn development. A total of 11,054 and 43,078 arthropods were collected in 2020 and 2021, respectively. The results have shown no impact of the corn planting dates with at-plant cover crop termination on arthropods but identified that cereal rye cover crop supports greater Araneae activity while its alternative prey varied when compared to the no-cover treatment. Significant yield penalties were observed when cover crop was used regardless of the corn planting dates. Pest pressure was not significant in any year, however, future research using cereal rye and different cover crop species should be used in this system with an artificial infestation of a pest to be able to evaluate the trade-offs between possible cash crop yield reductions and potential biological control of pests.

Impact of Cover Crop Planting and Termination Dates on Arthropod Activity in the Following Corn.

Relative to fallow-cash crop rotations, the addition of a cover crop can contribute to greater plant diversity and has the potential to conserve predatory arthropods. The transition of arthropods from a cover crop to a subsequent cash crop depends on several factors, such as cover crop biomass production and weather conditions. Information about the effect of cover crop planting and termination dates on arthropods in a subsequent corn system is limited. A two-year field study was conducted in Nebraska in 2018/2019 and 2019/2020 to evaluate the impact of cover crop planting and termination dates as a source for arthropods in the subsequent corn. A total of 38,074 and 50,626 arthropods were collected in the first and second year, respectively. In both years, adding a grass cover crop increased predatory arthropods but reduced yield in follow corn crop. Of the arthropods collected, Carabidae and Araneae had greater activity with cover crop biomass increments, whereas Collembola and Acari activity only increased in treatments with little or no cover crop biomass. Insect pest pressure was not significant in any treatment for either year. A cover crop planted in mid- or late-September and terminated at corn planting was identified as the best management strategy to maximize cover crop biomass, increase predator activity, and modify predator-prey dynamics. The results of this study provide growers with a cover crop management strategy to maximize cover crop biomass, beneficial arthropod activity, and potentially minimize insect pest problems; however, corn Zea Mays (L.) grain yield was reduced as cover crop biomass increased.