Location: Integrated Cropping Systems Research
2017 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 made substantial progress, producing fundamental, yet practical knowledge on the management of insect pests and weeds. Results of the current project may be used to reduce the impacts of weeds and insect pests on crops in Northern Plains farming systems via ecologically- and economically-sound pest management strategies, in accordance with the NP 304 Action Plan.
With regard to Objective 1, new research on corn rootworms is challenging the assumption that adult beetles will be equally fit when they feed on various transgenic corn varieties expressing the Cry3Bb1 toxin, as toxin levels may differ among varieties. To investigate this, we developed a greenhouse procedure that supplies ample leaves, silks, and pollen from corn plants to feed adult beetles year-round in experiments. We are using the procedure in a preliminary test to vet acceptably high survival of adults for use in future mating experiments.
In addition, profiles of early season sporadic pests were produced 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 the crops. These profiles will 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 management options.
Finally, under Objective 1, research on management of the soybean aphid progressed with the second year of field evaluations of the efficacy and impact of a soybean variety that has been pyramided with two aphid-resistance genes. The plots were also being sampled to determine the impact on non-target insects.
With regard to Objective 2, work was completed to refine tactics to manage clovers that organic producers use to suppress weeds in row crops in lieu of tillage. In addition, evaluations continued with annual clovers underseeded in small grains to control post-harvest weeds without tillage and to also measure winterkill of the clovers.
Accomplishments
1. Preceding crop impacts alfalfa’s competitiveness with weeds. Alfalfa has the ability to greatly benefit crop rotations because of its ability to suppress weeds, but the particular sequence of alfalfa within the rotation may make a substantial difference. ARS scientists at Brookings, South Dakota found that establishment of alfalfa was greatest when planted in the spring that follows soybean harvest and reduced when following corn or spring wheat 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, attributable to reduced competitiveness with weeds because of lower alfalfa plant density. Thus, planting alfalfa in the spring that follows soybean harvest is best for stand establishment and subsequent competition with weeds.
2. Pollinator strips can take up a neonicotinoid insecticide and make it available to honey bees. Worldwide pollinator declines are attributed to various factors, including pesticide exposures to neonicotinoid insecticides. ARS scientists in Brookings, South Dakota measured the amounts of a neonicotinoid known as clothianidin in leaves and nectar of plants in pollinator strips and tested for clothianidin in honey and bee bread at organic farms and those using neonicotinoid seed treatments. Total glycogen, lipids, and protein from honey bee workers were determined. Leaf tissue and honey had similar concentrations of clothianidin between organic and seed-treated farms. Honey had seven-fold greater clothianidin concentration than nectar collected by bees. Bee bread from organic sites had substantially less clothianidin than that at seed-treated locations. Increasing concentrations of clothianidin in bee bread were related to decreased glycogen, lipid, and protein in workers. These results will be useful as scientists and regulators consider the effects of insecticides on pollinators.
3. New approaches for improving insecticide risk-assessment programs. When insecticidal products are formally evaluated for risks, indicator species must be selected for use in toxicity tests, but no formal system has been developed to determine whether proposed indicator species are relevant to a particular crop where products are proposed for use. ARS scientists at Brookings, South Dakota used molecular gut-content tests and network analysis to identify species that are likely to be exposed to plant-incorporated products, and that likely have important functional roles in food webs in the corn cropping system. Only nine of the 382 types of corn-field insects and other small invertebrates sampled met three ecological criteria of high abundance, corn consumption, and high food web connectedness for inclusion as indicator species; and only one of these, the insidious flower bug, has routinely been considered in risk assessment. The use of large-scale field inventories of insects and other invertebrates, molecular gut-content tests, and ecological network analysis can be used in future insecticide risk-assessment programs.
4. Preceding crop affects aphid infestations in soybean. Crop rotations can have important implications for pest management, but have never been tested against the soybean aphid, a major pest of soybeans. ARS scientists at Brookings, South Dakota investigated how aphids performed on soybeans preceded by spring wheat versus an oat/pea mixture. Peak aphid populations were reduced by 40% or more by planting spring wheat before soybeans relative to the oat–pea mixture in two out of three years. Adapting the crop rotation sequence so that soybean follows spring wheat may be a straightforward way for farmers to rely less on insecticides for managing aphids.
5. Plant-based odors attract beneficial insect predators in corn and soybean fields. A greater knowledge of plant-based chemicals that attract beneficial insects may be especially valuable for management of agricultural crops as a practical means of enhancing ecosystem services. ARS researchers in Brookings, South Dakota found that predatory green lacewings and flower flies within corn and soybean plots were drawn to traps baited with particular plant-based attractants over others. The study documented novel attraction of green lacewings to the chemicals eugenol and isoeugenol and the attraction of flower flies to eugenol. These attractants may be useful to pest management practitioners in developing strategies to lure green lacewings, flower flies and other beneficial insects into corn and soybean fields to fight plant pests.
6. Low risk of western corn rootworm (WCR) going rogue from a strain with no metabolic resting stage. Many insects, like the WCR, utilize a metabolic resting stage, known as diapause, to pass stressful environmental periods such as extreme winter temperatures. WCR, a major pest of corn, has a non-diapausing (ND) strain that allows for continuous rearing and greatly facilitates laboratory and field experiments. However, there is concern that use of ND-WCR in field experiments might lead to its unintended establishment and thereby increase the threat to commercial corn production. ARS scientists at Brookings, South Dakota and Columbia, Missouri, in collaboration with Iowa State University researchers, found that mortality of ND eggs increased significantly when reared under conditions that would normally bring on diapause in the field. These results suggest that ND-WCR may be safely used in field research because it will not survive under typical yearly conditions in the U.S. Corn Belt.
7. A 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. ARS scientists at Brookings, South Dakota have found that a fall mowing tactic can convert red clover to corn production without needing either tillage or herbicides. Fall mowing reduces 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.
Review Publications
Lundgren, J.G., Hesler, L.S., Anderson, R.L. 2017. Preceding crop affects soybean aphid abundance and predator-prey dynamics in soybean. Journal of Applied Entomology. doi:10.1111/jen.12395.
Brandl, M., Schumann, M., French, B.W., Vidal, S. 2016. Screening of botanical extracts for repellence against western corn rootworm larvae. Journal of Insect Behavior. 29:395-414. doi:10.1007/s10905-016-9571-3.
Shrestha, R.B., Jakka, S.R., French, B.W., Gassmann, A.J. 2016. Field-based assessment of resistance to Bt Corn by Western Corn Rootworm (Coleoptera: Chrysomelidae). Journal of Economic Entomology. 109(3):1399–1409. doi:10.1093/jee/tow087.
Hesler, L.S. 2016. Volatile semiochemicals increase trap catch of Green Lacewings (Neuroptera: Chrysopidae) and Flower Flies (Diptera: Syrphidae) in corn and soybean plots. Journal of Insect Science. 16(1):77. doi:10.1093/jisesa/iew057.
Hesler, L.S. 2016. Capture of non-target flies (Diptera: Lauxaniidae, Chloropidae, Anthomyiidae) on traps baited with volatile chemicals in field crop habitats. Psyche. doi:10.1155/2016/6938368.
Gassmann, A.J., Shrestha, R.B., Jakka, S.R., Dunbar, M.W., Clifton, E.H., Paolino, A.R., Ingber, D.A., French, B.W., Masloski, K.E., Dounda, J.W., St. Clair, C.R. 2016. Evidence of resistance to Cry34/35Ab1 corn by western corn rootworm: root injury in the field and larval survival in plant-based bioassays. Journal of Economic Entomology. 109:1872–1880. doi: 10.1093/jee/tow110.
Schumann, M., Tappe, B., French, B.W., Vidal, S. 2017. Semi field trials to evaluate undersowings in maize for management of western corn rootworm larvae. Bulletin of Insectology. 70:63-68.
Hesler, L.S. 2017. Attraction of Diabrotica barberi Smith and Lawrence (Coleoptera: Chrysomelidae) to eugenol-baited traps in soybean. Great Lakes Entomologist. 49:163-168.
Anderson, R.L. 2017. Impact of preceding crop on alfalfa competitiveness with weeds. Renewable Agriculture and Food Systems. 32:28-32.
