Location: Integrated Cropping Systems Research
2020 Annual Report
Objectives
Objective 1. Develop strategies to manage insects in cropping systems, focusing on biology with regards to resistance evolution, insect health and diversity, and the value of these strategies to sustainable crop production. [NP304, Component 3, Problem Statement 3A2].
Subobjective 1a. Assess the risk to susceptible western corn rootworm, and hence insect resistance management, from adult feeding on corn tissue expressing toxic Bacillus thuringiensis (Bt)-proteins.
Subobjective 1b. Evaluate neonicotinoid seed treatments for usefulness to U.S. crop production.
Subobjective 1c. Compare pest and beneficial insect levels between a soybean pest-management system that uses an aphid-resistant cultivar versus one that relies on conventional insecticides.
Subobjective 1d. Compare pest and beneficial insect levels, soil properties, plant growth, yield, and seed composition of soybean when grown alone and with an oilseed relay crop.
Subobjective 1e. Evaluate cover-cropping scenarios within crop rotations that encourage ecosystem services from beneficial insects.
Subobjective 1f. Develop procedures for hazard assessments of pesticides to non-target organisms.
Subobjective 1g. Establish exposure pathways for pesticides and non-target organisms and determine how plant diversity within the farmscape affects these exposure pathways.
Objective 2. Develop innovative strategies for managing weeds in dynamic cropping systems, and assess the benefits of these strategies that rely on bottom-up approaches to weed management (such as the use of cover crops) within diverse crop rotations. [NP304, Component 2, Problem Statement 2A2].
Subobjective 2a. Develop a methodology to convert red clover to cropland without tillage.
Subobjective 2b. Determine the best annual clovers to use as cover crops to control post-harvest weeds without tillage.
Approach
Pest management is crucial in cropping systems, and strategies to control weeds and insect pests need to be integrated with agronomic and other management goals to achieve sustainable cropping systems. In the northern Great Plains, corn rootworms, soybean aphids, and weeds greatly reduce agricultural productivity and profitability through yield loss and costly control measures. Widely adopted management tactics have initially reduced economic loss from these pests, but their utility needs reassessment in light of herbicide-tolerant weeds, insect adaptation to resistance transgenes, secondary pest outbreaks, and unwitting impacts on pollinators, natural enemies, and soil health. This project plan proposes research to address strategies used against major pests such as corn rootworms and soybean aphid, refine tactics for weed management in organic production systems, and determine the value and drawbacks to pest management and ecosystem services from diversifying crop rotations, incorporating cover crops, and using various plant-incorporated protectants. The research will be instrumental in developing management practices that increase farming efficiency and improve environmental and economic sustainability.
Progress Report
The research project generated knowledge about insect pest management approaches and weed management tactics applicable to sustainable cropping systems in the northern Great Plains. In accordance with Objective 1 regarding management of corn rootworm, scientists documented the first cases of resistance to corn expressing toxic Bacillus thuringiensis (Bt)-proteins in northern corn rootworm. This adds to reports of field control failures of Bt corn hybrids against western corn rootworms. Investigations conducted in Nebraska showed the importance of local cropping history on the prevalence of resistance to Bt toxins among western corn rootworm populations.
In addition, Objective 1 has addressed the problem of corn rootworm resistance to Bt corn, which has become a problem in the U.S. sooner than predicted. Studies tested whether resistance development may have been accelerated by Bt exposure favoring survival and mating of larger male rootworms. We found that large males mate more frequently than small males, with no difference in longevity. This advantage may set up a self-amplifying cycle that results in quicker development of resistant pest populations. Thus, models designed to predict how quickly rootworms develop resistance to Bt toxins in corn may need to account for male body size.
With regard to Objective 1 and the use of insecticidal seed treatments, profiles of early-season sporadic pests were published for each of four major U.S. field crops (i.e., corn, soybean, cotton and wheat), along with an overview of patterns in pest pressure across these crops. The profiles in these five review articles may be used to understand factors involved with economic infestations of these early season pests to identify knowledge gaps associated with the pests, and to clarify the various pest management options, particularly with regard to insecticide seed treatments.
Additional research under Objective 1 on the management of soybean aphid concluded with regard to field evaluations on the efficacy and impact of a soybean variety that has been pyramided with two aphid-resistance genes. The resistant variety thwarted aphid infestations across the three years of the study, and there was no yield drag from use of the resistant variety. The plots were also sampled to determine the impact on non-target insects. The identification of the non-target species is ongoing due to the uncommonness of several taxa, and the analysis of any impact on these species will be completed shortly after the project terminates.
With regard to Objective 2 and weed management in cropping systems, the use of the diversification of plantings within crop rotations with specific perennial crops and cover crops was shown to improve crop competitiveness with weeds in two instances. First, alfalfa has the potential to greatly benefit crop rotations because of its ability to suppress weeds and improve soil quality. We found that establishment of alfalfa was reduced when following corn or spring wheat (compared with soybean) due to interference from crop residue and volunteer crop plants. Weed density was 18-fold higher in the third year of alfalfa when it followed spring wheat compared with soybean, because the lower alfalfa plant density increased competition from weeds. Thus, planting alfalfa in the spring that follows soybean harvest is best for stand establishment and subsequent competition with weeds. These results can help producers devise cropping rotations that provide multiple benefits.
Further research related to Objective 2 demonstrated a successful mowing strategy to convert red clover to annual crops in organic farming. Organic producers are interested in reducing tillage in their farming systems. A rotation that includes a perennial legume will help manage weeds, but tactics are needed to eliminate the legume to grow annual crops. The fall mowing tactic developed by ARS researchers at Brookings, South Dakota, can convert red clover to corn production without tillage or herbicides. In addition, fall mowing reduced the quantity of carbohydrates stored in the roots, thus enhancing winterkill. An ancillary benefit of no-till conversion of legumes to annual crop production is that weed seedling emergence is 80% less than after a tilled conversion. Also, weed emergence is delayed 2 to 3 weeks, further minimizing impact of weed interference on crop yield. This strategy increases the possibility of organic producers developing a no-till system.
Sulfonylurea herbicides are used worldwide to control weeds in major crops. They have low application rates, but carryover can injure crops, and they have been detected in groundwater. Therefore, a study was conducted that measured how these herbicides partition between soil and water to more accurately predict benefits (weed control) and detriments (crop damage, water contamination). Results demonstrated that (1) behavior of the herbicides does not necessarily represent the behavior of breakdown products with similar chemical structure; (2) results from one geographical region cannot be reliably generalized to another region; (3) partitioning determined for surface soils cannot be reliably extrapolated to nearby soils; and (4) sorption values alone do not characterize herbicide availability for leaching or plant uptake. These results can be used by regulators and herbicide registrants to delimit predictions about herbicide fate among soil types and geographic regions.
Results of the current project may be used to reduce the impacts of insect pests and weeds in continuously cropped corn systems and crops in sustainable farming systems of the Northern Plains.
Accomplishments
1. Collection data extends known geographic range of eight lady beetle species. Most lady beetles are voracious predators of insects and mites, and several feed on important agricultural pests. Despite their importance as natural enemies, fundamental knowledge of many lady beetle species is lacking, including up-to-date information about their geographic distributions. In two studies, researchers at ARS, Brookings, South Dakota, and Chadron State University, Nebraska, scrutinized insect collections at various institutions and the collection data associated with lady beetles to uncover new records that extended the known geographic distribution of eight species of predatory lady beetles in the United States. These findings highlight the importance of insect collections as valuable resources for extending fundamental knowledge about lady beetles and support the notion that systematic updated analysis of collection data will yield new insights into their geographic ranges and improve understanding of biodiversity.
2. Laboratory tests with the northern corn rootworm establish its baseline susceptibility to Bt corn toxins. The northern corn rootworm (NCR) is an economic pest of continuous corn in the Midwestern U.S. and is currently managed primarily with transgenic corn lines expressing insecticidal proteins from a bacterium known, in short, as “Bt.” The U.S. Environmental Protection Agency requires registrants of rootworm-targeted Bt products to develop and implement a resistance management plan for NCR. To help meet this requirement, researchers at ARS laboratories in Brookings, South Dakota, and Columbia, Missouri, and at the University of Missouri conducted various efficacy tests against NCR using Bt plants and with artificial diets overlaid with one of four Bt toxins, i.e., eCry3.1Ab, mCry3A, Cry3Bb1, and Cry34/35Ab1. The tests were conducted against an NCR strain collected and established as a rearing colony before the introduction of Bt corn into agricultural systems. The results of all tests showed that NCR was susceptible to each of the four Bt toxins. The findings are important to companies that produce corn hybrids and to researchers for establishing baseline levels of toxicity against NCR and for monitoring resistance evolution in NCR field populations.
3. Landscape favorability determines emergence rate of weed seeds in subsequent years. Because competition with weeds is often a primary factor limiting crop growth, effective weed management options are needed to support efficient crop production. The effects of soil temperature, moisture and other factors on the emergence and development of weed seedlings is a subject of significant study, but relatively little information is available regarding differences in the success of weed seeds as affected by the microsite in which they developed and overwintered. Researchers in Brookings, South Dakota, conducted a two-year field study to evaluate the viability of seeds of a pervasive weed (common lambsquarters) as affected by the landscape position in which they were grown. Results indicated that a higher proportion of seeds originating from lower slope positions emerged compared with seeds originating from the backslope or upper slope. The timing of emergence was the same for all seed source locations. There was no influence of overwintering location on weed emergence. We observed faster emergence and growth of lambsquarters planted in the lower slope, where soil conditions were more conducive to growth. These experiments will support weed scientists and field managers in the development of new strategies and decision aids to improve weed management.
Review Publications
Papiernik, S.K., Forcella, F., Amundson, G.B. 2020. Emergence of common lambsquarters (Chenopodium album L.) is influenced by the landscape position in which seeds developed. Agric Environ Lett. 5(1):e20000. https://doi.org/10.1002/ael2.20000.
Hesler, L.S. 2020. New state records of lady beetles (Coleoptera: Coccinellidae: Coccinellinae) from Missouri and Mississippi, U.S.A. Insecta Mundi. 0745: 1-4.
Hesler, L.S., Brust, M.L. 2020. New records of Coccinellidae (Coleoptera) from the central United States. Journal of Kansas Entomological Society. 92:488–491. https://doi.org/10.2317/0022-8567-92.2.488.
Pereira, A.E., Huynh, M.P., Sethi, A., Miles, A.L., French, B.W., Ellersieck, M.R., Coudron, T.A., Shelby, K., Hibbard, B.E. 2020. Baseline susceptibility of a laboratory strain of northern corn rootworm, diabrotica barberi (coleoptera: chrysomelidae) to bacillus thuringiensis traits in seedling, single plant, and diet-toxicity assays. Journal of Economic Entomology. 113(4):1955–1962. https://doi.org/10.1093/jee/toaa107.
