Project : USDA ARS

ARS Home » Plains Area » Brookings, South Dakota » Integrated Cropping Systems Research » Research » Research Project #430020

Research Project: Productive Cropping Systems Based on Ecological Principles of Pest Management

Location: Integrated Cropping Systems Research

2018 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 insect pests and weeds on crops in Northern Plains farming systems via ecologically- and economically-sound pest management strategies, in accordance with the NP 304 Action Plan. Progress in Objective 1a built upon previous scientific reports suggesting that adult corn rootworms can survive on corn leaves, silks, and pollen expressing the Cry3Bb1 transgenic toxin. However, differences in the level of toxin expression among corn varieties may affect the ability of resistant and susceptible individuals to produce viable offspring. We have paired over 300 combinations of resistant and susceptible males and females fed a diet of either Bt or non-Bt corn tissue. Thus far, no effect on egg production has been detected from these pairings. In Objective 1b, 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 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. Finally, in Objective 1c, research on management of the soybean aphid progressed with a third 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 sampled to determine the impact on non-target insects, and the samples are being processed.

Accomplishments
1. Molecular mechanisms of diapause in corn rootworms. The western corn rootworm and northern corn rootworm are serious pests of corn in the Midwestern U.S. Each species has one generation per year and overwinters as eggs in a dormant state known as diapause. Preemption of diapause capabilities could be exploited as a control method if the underlying genetic mechanisms were understood. To this end, ARS scientists at Brookings, South Dakota, are sharing non-diapausing strains of corn rootworms they developed in the laboratory with collaborators at the University of Kentucky so that the genes that regulate diapause may be identified and characterized. Knowledge of the genetics underlying diapause in corn rootworm is important to develop advanced research tools and may be used to develop a species-specific control strategy that precludes these pests’ ability to overwinter in crop fields.

2. New sampling technique reveals that corn rootworm damage is most acute in corn roots adjacent to the stem. Good techniques are lacking to reveal which portions of root systems are most affected by insect feeding. In a 2-year field study, ARS scientists at Brookings, South Dakota, evaluated corn root injury by western corn rootworm larvae using a novel technique known as a monolith soil–root sampler. Soil blocks removed by the monolith technique were partitioned into smaller grid samples and root lengths were measured. Root length density (total length of roots in a cube of soil) was determined for each grid sample, and root length densities were visualized using contour plots. These plots revealed dramatic feeding injury reductions in the portion of the root system closest to the plant stem. Monolith techniques, which quantitatively estimated reductions in root-length density from feeding by corn rootworm larvae, may be broadly applicable to future field studies that investigate below-ground crop damage from subterranean pests. Scientists, extension specialists, and educators can use the technique to study, for example, root injury-yield loss relationships for other pests or pathogens, interspecific competition between pests, and other interactions within the below-ground food web.

3. New collection on early-season pest risks in major U.S. crops. Seed treatments of neonicotinoid insecticides account for a significant portion of pesticide applied to many of the major U.S. crops to combat early-season and often sporadic pests. A clearer understanding of factors that influence the risk of economic infestations and crop damage by early-season pests is needed to improve decisions about using neonicotinoid seed treatments. Accordingly, profiles of pests listed on labels for three common neonicotinoid seed treatments (clothianidin, thiamethoxam, and imidacloprid) on four crops with the most acreage in the U.S. (corn, cotton, soybean, and wheat) were developed by ARS scientists at Brookings, South Dakota; Ames, Iowa; and Stoneville, Mississippi. The pest profiles focused on the frequency of economic infestations in the absence of preventative measures and on factors that affect the risk of economic infestation in a given field. The profiles showed that risk factors are pest-specific and can include geographic region, soil type, topography, cropping landscape, planting date, rotation scheme, tillage, weeds, and other variables. The reviews point out the complexity of predicting and managing a suite of highly-variable insect pests for which post-infestation (rescue) treatments are often unavailable. Through these publications and associated presentations, the pest profiles provide farmers, pest management practitioners, regulators, and policy analysts with information to make more-informed decisions about the need for preventative treatments against early-season sporadic and minor pests in the four major crops.

4. Multiple lines of resistance against soybean aphid ready to be exploited. The soybean aphid, an invasive insect pest that causes serious yield loss to soybean in the Midwest, has become resistant to one type of commonly used insecticide. Thus, there is heightened need to develop alternative control methods, such as aphid-resistant soybean cultivars. However, developing such cultivars is a challenge because various forms of the soybean aphid, known as biotypes, can overcome one or even two previously identified resistance genes. ARS scientists at Brookings, South Dakota, and researchers at South Dakota State University identified many lines of domesticated and wild soybean with resistance to soybean aphid. The large number of newly identified resistant lines increases the odds that researchers will find novel genes that can be combined to develop soybean cultivars that effectively counter the gamut of virulent soybean aphid biotypes, and several of the lines have been advanced for further testing against virulent soybean aphids.

U.S. DEPARTMENT OF AGRICULTURE

Integrated Cropping Systems Research: Brookings, SD