Project : USDA ARS

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Research Project: Biological Control and Habitat Restoration for Invasive Weed Management

Location: Pest Management Research

2022 Annual Report

Objectives
Objective 1: Determine the taxonomic identity, origins, evolutionary relationships, reproductive strategies, and/or population genetic information of target invasive weeds, such as bindweed (Convolvulus arvensis), African rue (Peganum harmala), houndstongue (Cynoglossum officinale), leafy spurge (Euphorbia esula/virgata), whitetop (Lepidium draba), and flowering rush (Butomus umbellatus). Subobjective 1.A: Determine correct taxonomy (Euphorbia complex) and native origins (Euphorbia complex, flowering rush) to support the successful development of classical biological control programs. Subobjective 1.B: Determine the population structure (African rue, bindweed, houndstongue, Euphorbia complex) and reproductive strategies (bindweed, Euphorbia complex) ) and hybrids (Euphorbia complex, whitetop) to support the successful development of classical biological control programs. Objective 2: Improve selection criteria and implementation of biological control agents of the targeted invasive weeds. Subobjective 2.A: Identify demographic and habitat factors associated with management impacts on Russian olive and whitetop populations. Subobjective 2.B: Disentangle large-scale variation in agent and weed distributions to improve biological control implementation and integrated weed management of leafy spurge (Euphorbia complex). Objective 3: Develop effective community restoration technology for disturbed and weed impacted areas. Subobjective 3.A: Determine priority tools and strategies for effective restoration of riparian ecosystems after Russian olive control. Objective 3.B: Determine impacts on pollinator communities after renovation of exotic cool season grasses to functional CRP.

Approach
Weeds cost U.S. agriculture billions of dollars annually in lost production and control costs. The goal of our project is to decrease weed abundance by increasing the efficacy of biological control agent development and improving the establishment success of plant community restorations that resist invasion. Our team’s research spans multiple aspects of weed control, from taxonomy required for effective development of weed management strategies, demographic and ecological research to optimize biological control management efficacy, and identification of inputs required to support productive invasion-resistant landscapes. We will address critical gaps in genotype-specific information regarding the reproductive strategies, origin and invasiveness of some of the most important invasive weeds in the U.S., thus guiding effective control methods including effective biological control. We will identify ecological and demographic factors limiting invasion potential for weeds targeted for biological control. This will generate strategies to limit target weed spread and provide a general framework of biologically- and ecologically-based weed control methods. We will also create realistic targets for restoration that benefit landscapes. This work develops science-based, economical weed management that reduces costs, promotes food security and minimizes negative environmental impacts of traditional weed control. We focus on rangeland weeds in the Northern Great Plains and extend this research nationally across a range of habitats. By communicating our results through on-going relationships with land management agencies, farmers and ranchers, academic societies, industry and state extension services, this research supports innovative strategies vital to the sustainability and health of U.S. agroecosystems.

Progress Report
Objective 1: ARS scientists in Sidney, Montana, continued DNA analysis of critical invasive plant species in the western United States and from their putative origins in Eurasia, including Russian knapweed, whitetop, leafy spurge, common crupina, common reed and flowering rush. They are now using molecular markers to determine the correct invasive species identification, major mode of reproduction, as well as specific origin of these invasions. This information is being used to develop more effective foreign biological control agents to fight against invasive plants in the United States. Objective 2: Effective biological control requires targeting vulnerable stages of a weed’s life cycle. Experimental field populations help us to understand the impacts of biocontrol, as we often lack basic biological data necessary to model and predict outcomes over time and with additional management strategies. ARS researchers, in collaboration with university, U.S. Geological Survey, and ARS partners, are using transplant experiments, seed additions, and common garden manipulations to examine how habitat and resource conditions affects the degree to which insects limit the persistence and population growth of whitetop/hoary cress, Russian olive, leafy spurge, and common crupina. These data will lead to better quantitative models and predictions of biocontrol impacts, recommendations and best practices for weed biocontrol, and expand integrated management options for low-input rangeland systems. Objective 2: ARS researchers at Sidney, Montana, have recently completed a multi-year survey of leafy spurge abundance and biological control agent communities across North Dakota, Montana, and Idaho. These data will inform our understanding of the status of the leafy spurge biological control program in the northern Great Plains and intermountain West, and provide crucial insight on where biocontrol is most effective, what agents are the most damaging, and how biocontrol management can be improved across a broad range of the most highly invaded region in the U.S. Objective 2: New research by ARS scientists at Sidney and Miles City, Montana, will be assessing fire effects on Russian olive seedlings and saplings. While adult Russian olives persist via resprouting after prescribed fire, seedling and sapling tolerance to fire is unknown. Western land managers spend thousands of dollars and labor hours annually to remove and control Russian olive. Without strategies to inhibit early colonizers and re-invasion after removal, such investments will only yield short-term benefits. This research will facilitate the development of cost-effective Russian olive management and post-removal control strategies for producers across the range of Russian olive invasion. Objective 3: ARS researchers at Sidney and Miles City, Montana, are using a ten-year post-removal and restoration experiment to examine the impacts of Russian olive invasion and post-removal restoration on plant and insect communities, pollinators, and floral resources. A census of all planted species and plant community data was conducted, and insect, pollinator, and pollinator resources assessed monthly throughout the growing season. Information gathered is being used to assess how Russian olive removal impacts natural communities and the scale of management required to achieve sustainable and productive control. Objective 3: Leafy spurge remains a highly problematic weed throughout the western U.S. and flowers for an extensive portion of the growing season. Numerous pollinating insects, including honeybees, are attracted to the flowers for pollen and nectar. However, no data are available to assess which pollinating insects are utilizing leafy spurge flowers, and how the extent and removal of leafy spurge infestations might influence pollinator populations. ARS researchers at Sidney, Montana, and collaborators surveyed leafy spurge populations for pollinators via sweep netting across Montana, North Dakota, and Idaho. Numerous families of pollinating insects have been found visiting leafy spurge. These data will be used to evaluate how leafy spurge competes with native range plants for pollination services from honeybees and native pollinators. Objective 3: ARS researchers at Sidney, Montana, are performing multi-year field studies to determine the impacts of fire and grazing on competition between native and invasive grasses in the northern Great Plains. The study integrates plant physiological and soil chemical and biological data to investigate mechanisms that lead to productivity differences among species in response to management. This information will assist in developing broad and transferable management strategies for invasive grass management across the Great Plains.

Accomplishments
1. Exact distribution of varieties and genotypes of a federal noxious weed found. Common crupina is a federal noxious weed in the western U.S. that forms solid stands and reduces the quantity and quality of forage. ARS researchers at Sidney, Montana, using molecular tools, genotyped the invasion and have determined exact distribution of the two varieties and seven genotypes of the invasion. A fungal biological control agent that causes significant reduction in crupina growth and seed production is proposed for release by ARS in 2022. The molecular research will allow monitoring of efficacy of the fungus on all plant genotypes in many habitats, ultimately increasing efficiency of the biological control program.

2. Reproductive variation across the range of Russian knapweed may influence biocontrol efficacy. To manage invasive plant species effectively we often need to know how they reproduce. ARS researchers at Sidney, Montana, used genetic markers to determine how recruitment of invasive Russian knapweed (Acroptilon repens) varies across its range. This species forms patches and can spread by both root growth and seed. We found no shared genotypes between 41 western North American populations, indicating that Russian knapweed is spreading via seed to distant locations. We found a correlation between latitude and clonal vs. seed reproduction, with clonality (spreading by roots) in populations higher in northern latitudes. This trend was associated with decreasing maximum annual temperature and 30-year average of available growing degree-days and increasing soil organic carbon content. These results have management implications: if not properly implemented, grazing or herbicide applications that create open spaces for recruitment may increase the likelihood of Russian knapweed patch persistence through seed, and recently released galling biological control agents in North America may be less effective in northern latitudes where Russian knapweed spread by seed is less prevalent.

3. Seeds increase leafy spurge abundance. Understanding if weeds are reproducing primarily through clones or seedling recruitment is particularly important for sustained management with biological control (biocontrol), as it relies on specialized insects with selective feeding patterns to limit weed populations. ARS researchers at Sidney, Montana, surveyed weed density, genetic diversity, and associated biocontrol agent abundance (Aphthona species flea beetles) in 100 leafy spurge populations across North Dakota, Montana, and Idaho. This survey provided insight into 1) how frequently seedlings contribute to population growth, and thus the density of leafy spurge infestations; and 2) whether leafy spurge density is related to the abundance of biocontrol agents and the balance between clonal and seedling recruitment into local populations. We found evidence of frequent recruitment from seed at all sites. Aphthona spp. flea beetles were everywhere, but the association between the number of flea beetles and leafy spurge density was not consistent. Increased importance of seed production may be changing the most effective targets for biocontrol after decades of Aphthona pressure on leafy spurge invasions. Further testing is needed to ensure biocontrol management is sufficient for long-term sustainable control.

4. Pollinators associated with Russian olive. Russian olive is spreading and limiting native vegetation within riparian zones. A biological control program that targets flowers and seed production is under development to limit Russian olive spread. However, we still know little about how flower damage that deters pollinators might influence the likelihood of Russian olive seed production and what pollinators utilize Russian olive flowers. ARS researchers at Sidney, Montana, used an insect exclusion experiment to determine whether Russian olive depends on insects for pollen transport and consequent seed production. Additionally, flower visiting insect surveys were conducted over a two-year period. Overall, we found numerous insect species visiting Russian olive flowers. These included 13 polylectic native bee species, but the dominant flower-visitor were western honey bees, which comprised over 80% of all insect visits. Nearly 35% of flowers that were allowed potential insect visitation produced fruit/seeds compared to 5% of flowers in which insect visitation was excluded. Our data supports that numerous insects will utilize Russian olive flowers and that insect visitation is needed for high fruit/seed output. However, honey bees were the most frequent floral visitors, and Russian olive flowers may provide a less frequent resource for native pollinators.

5. Mammals play an understudied role in Russian olive seed dispersal. Russian olive produces large berries that should attract seed consumption by vertebrates, but few data are available on the potential for seed dispersal by animals. ARS scientists at Sidney, Montana, gathered coyote and porcupine fecal material from within Russian olive windbreaks. Numerous intact Russian olive seeds were found within the scat and these seeds were used to perform germination tests. Overall, seeds passed through coyote and porcupine intestinal tracts germinated equally or higher than control seeds (not passed through an intestinal tract). These data provide some of the only empirical evidence that viable Russian olive seed can be spread via endozoochory (seed movement by animals) from mammals. This is also the first documented occurrence of endozoochory of any plant species by porcupines. Due to this novel finding, this research was recently highlighted by The Wildlife Society.

6. Developing strategies to support invasive annual grass management. Invasive annual grasses such as bromes (Bromus spp.), ventenata (Ventenata dubia) and medusahead (Taeniatherum caput-medusae) are problematic throughout arid and semi-arid rangeland ecosystems of the western United States, with substantial impacts to ecosystem health and forage productivity. ARS researchers at Sidney, Montana, along with collaborators, are developing effective control strategies that reduce wildfire spread and documenting invasive annual grass responses to fire in the Great Plains. Researchers employed United States Forest Service fire spread models in a first-of-its-kind exercise to determine which plant traits contribute to effective greenstrips (linear strips of less-flammable species planted to interrupt wildfire spread) that provide fire protection and staging areas for firefighters to safely initiate control operations. Field data and remotely-sensed products were also combined to verify that rangeland fire management in the eastern Great Plains is compatible with strategies to limit the frequency and abundance of invasive annual grasses. These “lessons learned” from the Great Plains were included in national efforts to describe the total ARS impact on knowledge of invasive annual grass management.

7. Cutting-edge tools for measuring fire effects on soil properties. Wildland fires can transform soil biological, chemical, and physical properties that play a critical role in competition between native plants and weeds. Estimating belowground heat and heat transfer through the soil is essential for understanding how plant-soil feedbacks vary across spatially complex fire footprints. Measuring below-ground temperatures during fire has been extremely challenging for fire scientists. ARS researchers at Sidney, Montana, together with collaborators at the University of Nevada and United States Forest Service, developed an open-source modeling tool to understand soil heating and heating effects across depths over time (the Soil Heating in Fire model; SheFire) and developed a novel data collection method that provides temperature data at multiple depths and minimizes soil disturbance and installation time (iStakes). The SheFire framework and iStakes provide a cutting-edge approach for characterizing soil heating through a soil profile and predicting biological responses, advancing the capability to assess how below-ground responses to wildland fire will impact weed invasions.

U.S. DEPARTMENT OF AGRICULTURE

Pest Management Research: Sidney, MT