Sources of Variability in Agronomic Weed Seed Predation: Time, Space, Habitat, and Hyperpredation

Weed seed predation is an ecosystem service that benefits farmers by decreasing seedbank inputs, thereby reducing weed pressure in subsequent growing seasons. Seed predation can be considerable, but is highly variable. Sources of variability may include time, space, habitat, and trophic interactions such as hyperpredation. Two experiments were conducted to measure the impacts of these sources of variability on weed seed predation rates in Maine mixed vegetable agroecosystems. Chapter One of this thesis describes a series of landscape-level field experiments conducted to quantify the effects of time, space, and habitat on seed predation rates. Seed assays, with and without vertebrate exclosures, were used to measure seed predation at spatially explicit sample sites across crop and non-crop habitats on a ‘typical’ Maine organic mixed vegetable farm. Total and invertebrate seed predation averaged 8% and 3% day-1, respectively. Motion-sensing wildlife cameras indicated that vertebrate seed predators included small mammals and birds. Pitfall trapping data indicated that one species of carabid, Harpalus rufipes, was highly dominant, comprising 66% of invertebrate seed predators captured within crop fields. Correlogram analysis showed that seed predation was randomly distributed in space. Based on linear mixed effects models, time and habitat were highly significant drivers of seed predation. Total seed predation varied between years of study, and both total and invertebrate seed predation decreased from August to October with winter’s approach. Total seed predation was greater in crop and riparian forest habitats than in mowed grass, meadow, or softwood forest. Generally, invertebrate seed predation was greatest at sites with moderate habitat complexity, while habitat type was the chief biotic determinant of vertebrate seed predation rates. In this study system, time and habitat were more important regulators of seed predation than was space. Chapter Two describes an experiment conducted to measure hyperpredation of H. rufipes and explore its effects on the weed seedbank. H. rufipes prefer sites with vegetative cover to fallow sites, preference speculated to be driven by predator avoidance behavior. To test this hypothesis, ‘hyperpredation assays’ were developed, in which live H. rufipes prey were presented to higher-order predators. Field trials were conducted to determine foremost if H. rufipes was subject to predation, and secondly, whether a) vegetative cover affords H. rufipes protection from hyperpredators, and b) high hyperpredation rates correspond with decreased invertebrate seed predation rates. Hyperpredation was 2.8% per day. Motion- sensing cameras indicated that H. rufipes’ predators included birds and small mammals. Neither a relationship between hyperpredation and vegetative treatment, nor an empirical relationship between hyperpredation and invertebrate seed predation were found. However, a simulation model predicted that hyperpredation at the rate observed could increase seedbank inputs by more than 17% annually. Additionally, complex habitats supported higher rates of hyperpredation than did simple habitats

Multi-Tactic Ecological Weed Management in a Changing Climate

Climate change is expected to impact weed communities in Maine, and the efficacy of tools and tactics farmers use to manage them. Through seedbank sampling and surveys of Maine organic farms, we identified currently rare weeds that are known to be especially abundant or problematic in warmer areas of the USA and might therefore represent an emerging agronomic risk. Many ecological weed management strategies that focus on depleting the weed seedbank are expected to remain effective in a changing climate, and become increasingly important as efficacy of cultivation and some herbicide applications diminish or become more variable. Through field experiments, we evaluated the efficacy of one seedbank management strategy, soil solarization (clear plastic) for stale seedbed creation. We found that two weeks of solarization followed by flaming created an effective stale seedbed, reducing subsequent weed density by 78% as compared to a control prepared with flaming only. In response to farmer questions, we measured solarization’s impacts on soil microbiota, and compared its weed control efficacy to that of tarping (black plastic). Soil biological activity was somewhat reduced by solarization, though results are likely temporary. Solarization was more effective than tarping in one site-year, but tarping outperformed solarization in the other. Overall, solarization is a promising weed management strategy for high-value crops, and one that is likely to remain effective in Maine’s changing climate. Maine is home to a growing population of beginning farmers, who face steep learning curves related to weed management. As a first step toward improving beginning farmer education, we constructed a digital tool called WEEDucator designed to engage users in interactive learning related to ecological weed management. Through a structured educational intervention we found that WEEDucator improved knowledge of weed ecology and management among agriculture students, and was ranked as a preferred learning method. Overall, the findings of this dissertation can aid in the development of outreach materials on climate-resilient ecological weed management practices suitable for farmers in Maine

Trials Evaluating Solarization and Tarping for Improved Stale Seedbed Preparation in the Northeast USA

Stale seedbeds are commonly used by organic vegetable farmers to reduce in-season weed density. The primary purpose of this study was to evaluate the efficacy of soil solarization (clear plastic) with subsequent flaming for stale seedbed preparation. A secondary objective was to compare the efficacy of solarization with tarping (black plastic). Solarization is an established weed management practice in warmer climates, but its efficacy in the humid continental Northeast USA was unknown. We hypothesized that solarization during May-June in Maine, USA would increase weed emergence, and could thereby contribute to depletion of the germinable weed seedbank and, with subsequent flaming, creation of an improved stale seedbed. We expected that firming soil with a roller prior to solarization would further increase weed emergence. Across four site-years of replicated field experiments and two on-farm trials we found that, contrary to expectations, 2 weeks of solarization reduced apparent weed emergence (density) in comparison to nonsolarized controls by 83% during treatment, and 78% after 2 weeks of observation following plastic removal and flaming. Rolling did not significantly affect weed density. Soil temperatures were elevated in solarized plots, reaching a maximum of 47◦ C at 5 cm soil depth, compared to 38◦ C in controls. Weed community analyses suggested that solarization might act as an ecological filter limiting some species. Addressing our secondary objective, two replicated field experiments compared the efficacy of solarization with tarping applied for periods of 2, 4, and 6 weeks beginning in July. Across treatment durations, solarization was more effective than tarping in one site-year, but tarping outperformed solarization in the other; this discrepancy may be explained by differences in weed species and soil temperatures between experiments. Overall, solarization and tarping are promising stale seedbed preparation methods for humid continental climates, but more work is needed to compare their relative efficacy

Using Farmer Storytelling to Build Understanding of Our New Weather Reality

A storytelling session was successful in raising awareness and understanding of the types of changes in weather patterns farmers are experiencing in Maine, what impacts those changes are having on their operations, and the changes farmers are making in response. Using an outreach approach rooted in farmer stories allowed us to bypass the controversy that often surrounds topics related to climate change. Likewise, focusing on the farmers\u27 experiences and avoiding corrective statements during this introductory session resulted in productive dialogue. We recommend replicating this approach within different agricultural sectors to increase understanding of sector-specific risks and strategies for adaptation

Effects of Field and Greenhouse Solarization on Soil Microbiota and Weed Seeds in the Northeast USA

Soil solarization using clear plastic is a promising weed management strategy for organic farms in the Northeast USA. Based on grower concerns that the practice might negatively affect beneficial soil microbiota, we conducted experiments to measure the effects of 2 and 4 weeks of solarization in a field and a closed greenhouse. Soil microbial communities were assayed by dilution plating on semi-selective agar media. Populations of general bacteria, general fungi, bacilli, and florescent pseudomonads were unaffected by field solarization, but fluorescent pseudomonads were reduced following greenhouse solarization. At plastic removal, soil biological activity was reduced non-significantly in the field and by 45% in the green- house. Soil biological activity fluctuated following field solarization, being significantly suppressed at 5 but not 14 days after plastic removal. In the greenhouse, biological activity remained suppressed up to 28 days after plastic removal. Solarization increased available nitrogen in the field and greenhouse. Four weeks of solarization reduced viability of buried weed seeds by 64% in the field and 98% in the greenhouse, indicating that the practice can cause substantial weed seed mortality. Maximum soil temperatures, measured at 10 cm depth under solarization, were 44◦ C in the field and 50◦ C in the greenhouse; temperatures were theoretically sufficient for the reduction of some soil borne pathogens. A subsequent experiment measured the effects of solarization and tarping (black plastic) on soil biological activity. During mulching, biological activity was unaffected by treatment, but 14 days after plastic removal, biological activity was reduced in the solarized treatment as compared with the control. Overall, these results suggest that solarization can deplete the weed seedbank. Although soil biological activity was reduced by solarization, it may bounce back after a period. Greenhouse solarization achieved higher temperatures and was more lethal to weed seeds and some microbiota than field solarization

UMaine Office for Diversity and Inclusion_ Happy Valentines and Self-Care! Email

Email from the UMaine Office for Diversity and Inclusion with various details of the Office\u27s work, Black History Month events, and featuring a letter from Dr. Sonja K. Birthisel Director of the Wilson Center regarding the Wabanaki peoples of Maine