BALANCING SOIL NUTRITION FOR SUSTAINABLE WEED AND PEST-INSECT MANAGEMENT

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: OTHER GRANTS
• Reporting Frequency: Annual
• Accession No.: 1020496
• Grant No.: 2019-51106-30188
• Cumulative Award Amt.: $499,993.00
• Proposal No.: 2019-03516
• Project Start Date: Sep 1, 2019
• Project End Date: Aug 31, 2024
• Grant Year: 2019
• Program Code: [112.E]- Organic Transitions

Recipient Organization
UNIVERSITY OF GEORGIA
200 D.W. BROOKS DR
ATHENS,GA 30602-5016

Performing Department
(N/A)

Non Technical Summary
Manure fertilizers bring many benefits for plant and soil health. However, because manure is not composed with an ideal balance of macro/micronutrients for crops, meeting the needs for nitrogen can lead to accumulations of surplus phosphorous. Nutrient imbalances, in turn, may exacerbate weed and insect pest pressure, bringing unexpected and unwelcome management costs to growers. We propose three research objectives to help transitioning organic farmers use fertility inputs to achieve balanced soil nutrition that maximizes profitability and optimizes pest management, focusing on zucchini crops (Cucurbita pepo subsp. pepo), due to their economic importance and challenging weed and insect problems. First, we will search for links between soil nitrogen, phosphorous, and densities of weeds and pests, on a network of more than 50 collaborating organic mixed-vegetable farms across the Southeast. Second, we will experimentally define how different manure compost application rates impact interactions between weeds, insects, and crop yield. Third, we will optimize combinations of cover crops and different compost fertilizers that improve nutrient balance while promoting natural pest suppression. Complementary economic analyses will allow growers to confidently ensure profitability while minimizing labor investments, while on-farm work with our large network of cooperating growers will ensure real-world applicability of our findings while facilitating outreach efforts. We will extend our findings to a broader audience through workshops, field days, and electronic media. Altogether, our project addresses ORG priorities by quantifying costs and benefits of organic manure composts for biodiversity, soil health, and natural pest control.

Animal Health Component

60%

Research Effort Categories

Basic

40%

Applied

60%

Developmental

0%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
216	1499	1070	100%

Knowledge Area
216 - Integrated Pest Management Systems;

Subject Of Investigation
1499 - Vegetables, general/other;

Field Of Science
1070 - Ecology;

Keywords

cucurbita pepo

biocontrol

herbivore resistance

manure fertilizer

pest management

weed mngmnt

Goals / Objectives
We propose three complementary research objectives.1. Search for links between soil N/ P levels and densities of weeds and pests, on a network of more than 50 collaborating, southeastern organic mixed-vegetable farms.By establishing an interactive network of collaborating farmers at this scale, we gather real-world knowledge, extend it through individualized engagement with farmers, and build natural outreach channels.2. Experimentally define how different manure compost application rates impact interactions between weeds, insects, and crop yield for organic zucchini crops.This will help us quantify time/money farmers invest in extra weed and pest management because of nutrient imbalances. Economic analyses of labor inputs under different fertility strategies will be shared with farmers during field days and through eOrganic videos.3. Optimize combinations of cover crops and blends of manure compost (high P) and food waste compost (lower P) to ease P buildup and limit pest susceptibility.We will test some potential solutions for the fertility and pest management challenges we define in Objective 2, alongside economic analyses comparing the relative merits of different fertility materials. In turn, these results will inform our field days and online videos.

Project Methods
Objective 1: Search for links between soil nitrogen, phosphorous, and densities of weeds and pest insects on a network of 50 collaborating organic vegetable farms across the Southeast.With our first objective, we will measure numerous plant-based variables (cover crop and weed diversity) and soil-based variables (micro and macronutrients, organic matter, microbial respiration, etc.) on working organic farms. We will gather this information through a massive on-farm survey project, supported by over 50 mixed-vegetable, organic farmers. Our survey teams will radiate from three locations in different regions of the Southeast with distinct soil and environmental characteristics: Charleston, Greensboro/Charlotte, and Athens/Atlanta. Many of our cooperating growers have integrated crop-livestock operations and incorporate animal-based fertility amendments into their soils; therefore, we expect to observe strong variation in soil microbial communities and invertebrate communities across sites. If we can detect broad patterns that persist among the significant ecological variation in our three survey regions, we can be confident that our results might have broader implications for many farmers throughout the region and country.Objective 2: Experimentally define how manure compost application rates impact interactions between weeds, insects and crop yield for organic zucchini crops.In this experiment, we will manipulate application rates of composted poultry manure at four levels to determine the point at which excess fertility begins to threaten profitability due to increased pest pressure. We focus on composted poultry manure because it is the most common organic fertility resource used in the Southeast. The five fertility treatments will be arranged in 6 x 8m plots in a latin square design, with 5 replicates (25 plots total). Plots will have five rows each, with 24 squash plants (C. pepo subsp pepo cvs. 'Yellow fin') per row, and data will be collected from the three interior rows. Weeds will be controlled with scuffle hoes bi-weekly (transitioning farmers often have limited access to expensive implements), and labor investments for each treatment will be estimated for economic analyses.Objective 3: Optimize combinations of cover crops and blends of manure compost (high P) and food waste compost (low P) to ease P buildup and limit pest susceptibility.Blending manure fertilizers with lower-P alternatives might improve nutrient balance and minimize pest pressure. To examine the role of surplus P in pest susceptibility for manure-fertilized crops, we will manipulate blends and concentrations of two commercially available organic fertility composts that vary in their N:P ratios. Poultry manure compost has a relative low N:P ratio (approximately 1.25) and more surplus P while food/yard waste compost has a relatively high N:P ratio (approximately 1.8), and more balanced P concentrations.Our experiment will be executed with 10 treatments over an ordinal gradient of P, holding total N constant (Plant-available N + potential mineralizable N). We will engineer this P gradient by varying the proportion of N coming from each fertility resource (poultry manure compost and food waste compost) in a substitutive design over 10 levels (Table 1), with four replicates of each level in randomized blocks (40 total 6 x 8m plots with five rows). Treatments with high proportions of N coming from poultry manure (e.g. Symphony® 5-4-3) will have relatively high concentrations of P, whereas treatments with high concentrations of food waste compost (e.g. Atlas Organics®, 1.1, 0.6, 0.39) will have relatively lower P. We have selected two fertility materials with similar concentrations of organic matter, but because we focus on commonly applied, commercially available, and agriculturally relevant organic fertilizers, other micro and macronutrients will vary. We will apply our gradient of N:P ratios in combination with the most common fall cover cropping strategy in our area: a fall cereal rye/clover cover crop which will be mowed and integrated in the spring in each plot ahead of our experiment. This approach will enable us to identify pest suppressive blends of manure and other organic fertility resources (cover crops and food waste compost) with lower P concentrations.

Progress 09/01/19 to 08/31/24

Outputs
Target Audience:The goal of our ORG project was to help farmers use fertility inputs to achieve balanced soil nutrition that maximizes profitability and optimizes pest management, focusing on zucchini crops (Cucurbita pepo subsp. pepo) due to their economic importance and challenging weed and insect problems. Our target audience was organic vegetable growers who rely on organic inputs to improve soil fertility, but often struggle to achieve soil nitrogen targets without adding too much phosphorous. In addition, we hope that our work provided basic insight into how soil nitrogen and phosphorous in the soil indirectly impact plants' ability to defend themselves against herbivorous insects, and compete with other plant species. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Three graduate students (Julia Berliner, Amy Sparer, and Carly Sharp), as well as undergraduate research assistants (Melina Madden, Andrew Godard, and Logan Johnson) were trained or were trained on this project. Melina and Andrew led efforts to quantify how weed pressure and weed management labor were influenced by surplus fertility applications, and Melina and Amy led on-farm surveys of soils and pests across South Carolina. Julia led a second year of a field experiment (Obj 2) in 2021, and Carly conducted a series of field experiments in the 2022-2024 growing seasons. How have the results been disseminated to communities of interest?Results were presented at a series of Entomological Society of America meetings, and in an annual webinars with our network of participating organic farmers. Youtube videos on identifying common pests and predators in cucurbit systems were composed. We also prepared display boxes of common pests and natural enemies in cucurbit production, and these have been presented during on-farm surveys and greatly appreciated by farmers who were previously unable to develop search images for common beneficial insects (many of whom are rather small and difficult to identify. We have engaged grower-collaborators on this project and have had on-farm discussions with most growers to gauge their concerns associated with fertility management. We prepared individualized reports of soil tests and biodiversity inventories of plants and insects for the farmers in our network. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Objective 1: Work with a network of over 50 organic mixed-vegetable farms in the Southeast to search for links between soil nitrogen, phosphorous, and densities of weeds and pests. We visited more than 50 organic farms across Georgia and the Carolinas, and collected soil samples, evaluated weed communities in quadrat surveys, performed visual surveys and vacuum samples of pests and natural enemies, and performed sentinel prey assays. We grew zucchini plants in soils collected from each farm in a common garden experiment, and measured rates of herbivore growth and pest suppression by natural enemies. We found that while herbivore growth did not correlate with increased soil N (as we predicted), omnivorous predators linked more tightly with soil N and plant quality, potentially counterbalancing effects of surplus fertility on pest growth. This research was published in the Journal of Animal Ecology. Objective 2: Experimentally define how different manure compost application rates impact interactions between weeds, insects, and crop yield. We completed a two-year field experiment manipulating concentrations of poultry manure fertilizers on zucchini plants. We predicted that surplus fertility conditions would exacerbate pest pressure, but found instead that pests had neutral or inconsistent responses to fertility, while natural enemies increased under surplus fertility conditions. These results were incorporated into project students Julia Berliner's MS thesis (defended fall 2022). A second manuscript evaluating the consequences of surplus fertility for weeds, pests, plant pathogens, and profitability is in preparation. Objective 3: Optimize combinations of cover crops and different compost fertilizers that improve nutrient balance while promoting natural pest suppression. MS student Janeva Williams & Co-PD Bhowmik (NC A&T) examined impacts of cover cropping and manure application on greenhouse gas emissions and impact of biochar application on soil enzymes as biological indicators of soil health. Janeva and Co-PD Bhowmik presented their research at seven conferences and workshops in 2021-2022, and defended her MS thesis in 2022. Co-PD Bhowmik also published a review paper on organic amendments that improve soil health in Frontiers in Microbiology. PhD student Carly Rae Sharp led an experiment manipulating ratios of nitrogen and phosphorus in organic fertility treatments on zucchini crops, and found that high concentrations of phosphorus (common in manure-fertilized systems) increased weed growth, while limiting crop growth and reducing attraction by beneficial insects, which indirectly increased pest pressure. Carly's research was presented at the Southeastern Branch meeting of the Entomological Society of America in 2023, and her work will be submitted for publication in 2025.

Publications

• Type: Peer Reviewed Journal Articles Status: Published Year Published: 2023 Citation: Blubaugh, CK. An omnivore vigour hypothesis? Nutrient availability strengthens herbivore suppression by omnivores across 48 field sites. Journal of Animal Ecology 92:751-759.

Progress 09/01/22 to 08/31/23

Outputs
Target Audience:The goal of our ORG project is to help farmers use fertility inputs to achieve balanced soil nutrition that maximizes profitability and optimizes pest management, focusing on zucchini crops (Cucurbita pepo subsp. pepo) due to their economic importance and challenging weed and insect problems. Our target audience is organic vegetable growers who rely on organic inputs to improve soil fertility, but often struggle to achieve soil nitrogen targets without adding too much phosphorous. In addition, we hope that our work will provide basic insight into how soil nitrogen and phosphorous in the soil indirectly impact plants' ability to defend themselves against herbivorous insects, and compete with other plant species. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?This project supported MS student Julia Berliner, and PhD student Carly Sharp. How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Objective 1: Work with a network of over 50 collaborating organic mixed-vegetable farms in the Southeast to search for links between soil nitrogen, phosphorous, and densities of weeds and pests. We visited more than 40 organic farms across Georgia and the Carolinas, and collected soil samples, evaluated weed communities in quadrat surveys, performed visual surveys and vacuum samples of pests and natural enemies, and performed sentinel prey assays. In 2021, we grew zucchini plants in soils collected from each farm in a common garden experiment, and measured rates of herbivore growth and pest suppression by natural enemies. We analyzed these data with the on-farm samples, and found that while herbivore growth did not correlate with increased soil N (as we predicted), yet omnivorous predators linked more tightly with soil N and plant quality. These results have been analyzed. Objective 2: Experimentally define how different manure compost application rates impact interactions between weeds, insects, and crop yield. MS student Julia Berliner repeated a field experiment manipulating concentrations of poultry manure fertilizers on zucchini plants. We predicted that surplus fertility conditions would exacerbate pest pressure, but they found that pests (mostly dominated by specialist squash bugs) actually declined under high fertility conditions, while natural enemies increased under surplus fertility conditions. These results have been analyzed. Objective 3: Optimize combinations of cover crops and different compost fertilizers that improve nutrient balance while promoting natural pest suppression. PhD student Carly Rae Sharp has been recruited and has begun leading field experiments to address this goal.

Publications

Progress 09/01/21 to 08/31/22

Outputs
Target Audience:The goal of our ORG project is to help farmers use fertility inputs to achieve balanced soil nutrition that maximizes profitability and optimizes pest management, focusing on zucchini crops (Cucurbita pepo subsp. pepo) due to their economic importance and challenging weed and insect problems. Our target audience is organic vegetable growers who rely on organic inputs to improve soil fertility, but often struggle to achieve soil nitrogen targets without adding too much phosphorous. In addition, we hope that our work will provide basic insight into how soil nitrogen and phosphorous in the soil indirectly impact plants' ability to defend themselves against herbivorous insects, and compete with other plant species. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Three graduate students (Julia Berliner, Amy Sparer, and Carly Sharp), as well as undergraduate research assistants (Melina Madden, Andrew Godard, and Logan Johnson) were trained on this project. Melina and Andrew led efforts to quantify how weed pressure and weed management labor were influenced by surplus fertility applications, and Melina and Amy led on-farm surveys of soils and pests across South Carolina. Julia led a second year of a field experiment (Obj 2), and Carly conducted a series of field experiments. How have the results been disseminated to communities of interest?Pest/predator display collections: in 2021, UGA students (led by Co-PD Blubaugh) curated six small display collections featuring the most common pests and natural enemies on organic farms for use in informal farmer training during on-farm visits and at outreach events. Pest/predator videos: In 2021 and 2022, UGA students (led by Co-PD Blubaugh) created 13 short, engaging videos featuring common pests and beneficial insects to aid farmers in identification. (link to YouTube playlist) What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Objective 1: Work with a network of over 50 organic mixed-vegetable farms in the Southeast to search for links between soil nitrogen, phosphorous, and densities of weeds and pests. We visited more than 50 organic farms across Georgia and the Carolinas, and collected soil samples, evaluated weed communities in quadrat surveys, performed visual surveys and vacuum samples of pests and natural enemies, and performed sentinel prey assays. In 2021, we grew zucchini plants in soils collected from each farm in a common garden experiment, and measured rates of herbivore growth and pest suppression by natural enemies. We found that while herbivore growth did not correlate with increased soil N (as we predicted), omnivorous predators linked more tightly with soil N and plant quality, potentially counterbalancing effects of surplus fertility on pest growth. Objective 2: Experimentally define how different manure compost application rates impact interactions between weeds, insects, and crop yield. MS student Julia Berliner and undergraduate Mary-Frances Behnke completed a two-year field experiment manipulating concentrations of poultry manure fertilizers on zucchini plants (mentored by Co-PD Blubaugh). We predicted that surplus fertility conditions would exacerbate pest pressure, but found instead that pests had neutral or inconsistent responses to fertility, while natural enemies increased under surplus fertility conditions. These results were incorporated in Julia's MS thesis (defended fall 2022) and are currently in-review at Ecology. A second manuscript evaluating the consequences of surplus fertility for weeds, pests, plant pathogens, and profitability is in preparation (Led by Blubaugh, with Cutulle and Vassallos). Berliner, J.T., Behnke, M.F., Hagan, K.L., and Blubaugh, C.K. Diet breadth mediates arthropod responses to nutrient availability across trophic levels. (In review at Ecology) Objective 3: Optimize combinations of cover crops and different compost fertilizers that improve nutrient balance while promoting natural pest suppression. During 2021 and 2022, MS student Janeva Williams & Co-PD Bhowmik (NC A&T) examined impacts of cover cropping and manure application on greenhouse gas emissions and impact of biochar application on soil enzymes as biological indicators of soil health. Janeva and Co-PD Bhowmik presented their research at seven conferences and workshops in 2021-2022, and defended her MS thesis in 2022. Co-PD Bhowmik also published a review paper on organic amendments that improve soil health in Frontiers in Microbiology. During summer 2022, MS student Carly Rae Sharp & PD Snyder (UGA) led an experiment manipulating ratios of nitrogen and phosphorus in organic fertility treatments on zucchini crops, and found that high concentrations of phosphorus (common in manure-fertilized systems) increased weed growth, while limiting crop growth and reducing attraction by beneficial insects, which indirectly increased pest pressure. Carly's research was presented at the Southeastern Branch meeting of the Entomological Society of America.

Publications

Progress 09/01/20 to 08/31/21

Outputs
Target Audience:The goal of our ORG project is to help farmers use fertility inputs to achieve balanced soil nutrition that maximizes profitability and optimizes pest management, focusing on zucchini crops (Cucurbita pepo subsp. pepo) due to their economic importance and challenging weed and insect problems. Our target audience is organic vegetable growers who rely on organic inputs to improve soil fertility, but often struggle to achieve soil nitrogen targets without adding too much phosphorous. In addition, we hope that our work will provide basic insight into how soil nitrogen and phosphorous in the soil indirectly impact plants' ability to defend themselves against herbivorous insects, and compete with other plant species. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Three graduate students (Julia Berliner, Amy Sparer, and Carly Sharp), as well as undergraduate research assistants (Melina Madden, Andrew Godard, and Logan Johnson) are currently being trained or were trained on this project. Melina and Andrew led efforts to quantify how weed pressure and weed management labor are influenced by surplus fertility applications, and Melina and Amy led on-farm surveys of soils and pests across South Carolina. Julia led a second year of a field experiment (Obj 2) in 2021, and Carly will lead one for objective 3 in 2022. How have the results been disseminated to communities of interest?Preliminary results were presented at the Entomological Society of America meeting virtually, and in an annual webinar with our network of participating organic farmers. Youtube videos on identifying common pests and predators in cucurbit systems have been composed will be published in 2021. We also prepared display boxes of common pests and natural enemies in cucurbit production, and these have been presented during on-farm surveys and greatly appreciated by farmers who were previously unable to develop search images for common beneficial insects (many of whom are rather small and difficult to identify. We have engaged grower-collaborators on this project and have had on-farm discussions with most growers to gauge their concerns associated with fertility management. Late in 2021, we prepared individualized reports of soil tests and biodiversity inventories of plants and insects for the farmers in our network. What do you plan to do during the next reporting period to accomplish the goals?Objective 1) This objective is technically complete, but we plan to continue on-farm sampling in the long-term to maintain ongoing relationships with farmers in our survey network. Objective 2) MS student Julia Berliner draft a manuscript examining how surplus macronutrients influence weeds, insect pests, and biological control services by natural enemies. These results will be communicated to growers in an annual webinar (February 2022), and at the Entomological Society of America Conference. Objective 3) MS student Carly Sharp will lead an experiment manipulating a gradient of N:P ratios in fertilizers by blending poultry manure (high P) with feathermeal-based fertilizers (low P) in cover cropped environments to reveal optimal cocktails of common fertility amendment materials that support crop productivity while minimizing pest susceptibility.

Impacts
What was accomplished under these goals? Objective 1: Work with a network of over 50 collaborating organic mixed-vegetable farms in the Southeast to search for links between soil nitrogen, phosphorous, and densities of weeds and pests. In 2021, we visited more than 40 organic farms across Georgia and the Carolinas, and collected soil samples, evaluated weed communities in quadrat surveys, performed visual surveys and vacuum samples of pests and natural enemies, and performed sentinel prey assays. In 2021, we grew zucchini plants in soils collected from each farm in a common garden experiment, and measured rates of herbivore growth and pest suppression by natural enemies. We analyzed these data with the 2020 on-farm samples, and found that while herbivore growth did not correlate with increased soil N (as we predicted), yet omnivorous predators linked more tightly with soil N and plant quality. These results have been analyzed, and a paper was submitted to Ecology in 2021. Objective 2: Experimentally define how different manure compost application rates impact interactions between weeds, insects, and crop yield. MS student Julia Berliner repeated a field experiment manipulating concentrations of poultry manure fertilizers on zucchini plants. We predicted that surplus fertility conditions would exacerbate pest pressure, but they found that pests (mostly dominated by specialist squash bugs) actually declined under high fertility conditions, while natural enemies increased under surplus fertility conditions. These results have been analyzed and presented at the Entomological Society of America meeting, and will be prepared for submission in 2021. Objective 3: Optimize combinations of cover crops and different compost fertilizers that improve nutrient balance while promoting natural pest suppression. MS student Carly Rae Sharp has been recruited to lead this experiment in the 2022 field season.

Publications

Progress 09/01/19 to 08/31/20

Outputs
Target Audience:The goal of our ORG project is to help farmers use fertility inputs to achieve balanced soil nutrition that maximizes profitability and optimizes pest management, focusing on zucchini crops (Cucurbita pepo subsp. pepo) due to their economic importance and challenging weed and insect problems. Our target audience is organic vegetable growers who rely on organic inputs to improve soil fertility, but often struggle to reach soil nitrogen targets without adding too much phosphorous. In addition, we hope that our work will provide basic insight into how soil nitrogen and phosphorous in the soil indirectly impact plants' ability to defend themselves against herbivorous insects, and compete with other plant species. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Three graduate students (Julia Berliner, Amy Sparer, and Carly Sharp), as well as three undergraduate research assistants (Melina Madden, Andrew Godard, and Logan Johnson) are currently being trained or were trained on this project. Melina and Andrew led efforts to quantify how weed pressure and weed management labor are influenced by surplus fertility applications, and Melina and Amy led on-farm surveys of soils and pests across South Carolina. Julia will lead our second year of a field experiment (Obj 2) in 2021, and Carly will lead our first year of experimental work under objective 3 in 2022. How have the results been disseminated to communities of interest?Preliminary results were presented at the Entomological Society of America meeting virtually, and shared via email with the farmers in our research network. eOrganic videos on identifying common pests and predators in cucurbit systems have been composed and submitted for publication through eOrganic. We also prepared display boxes of common pests and natural enemies in cucurbit production, and these have been presented during on-farm surveys and greatly appreciated by farmers who were previously unable to develop search images for common beneficial insects (many of whom are rather small and difficult to identify). We have engaged grower-collaborators on this project and have had on-farm discussions with most growers to gauge their concerns associated with fertility management. During each sampling round, we shared preliminary findings on how different pests might respond to fertilizer concentrations with our cooperating growers. What do you plan to do during the next reporting period to accomplish the goals?Objective 1) We have expanded our on-farm survey network to more than 40 farmers in NC, SC, and GA, and will collect and process samples collected in 2021, and combine them with our first year of on-farm survey data to examine relationships between concentrations of N and P with biodiversity among plants, herbivores, and natural enemies. Objective 2) MS student Julia Berliner will repeat the field experiment manipulating a gradient of fertility and draft a manuscript examining how surplus macronutrients influence weeds, insect pests, and biological control services by natural enemies. Objective 3) MS student Carly Sharp will lead an experiment manipulating a gradient of N:P ratios in fertilizers by blending poultry manure (high P) with feathermeal-based fertilizers (low P) in cover cropped environments to reveal optimal cocktails of common fertility amendment materials that support crop productivity while minimizing pest susceptibility.

Impacts
What was accomplished under these goals? Objective 1: Work with a network of over 50 collaborating organic mixed-vegetable farms in the Southeast to search for links between soil nitrogen, phosphorous, and densities of weeds and pests. Of course, due to the pandemic on-farm work was extremely challenging. Nonetheless, we have already completed on-farm sampling activities at 20 farms in South Carolina, and arranged for sampling across a wider region once travel restrictions ease. At each site, we collected soil samples and performed soil tests, evaluated weed communities in quadrat surveys, performed visual surveys and collected vacuum samples of pests and natural enemies, and performed sentinel prey assays. These data will be combined with samples collected in the 2021 field season, analyzed to determine how N and P concentrations relate to pest pressure and natural enemy attraction, and prepared for publication. Objective 2: Experimentally define how different manure compost application rates impact interactions between weeds, insects, and crop yield. PD Blubaugh led a field experiment with assistance from undergraduate researchers manipulating concentrations of poultry manure fertilizers on zucchini plants. We predicted that surplus fertility conditions would exacerbate pest pressure, but instead found that pests (mostly dominated by specialist squash bugs) actually declined under high fertility conditions, while natural enemies increased under surplus fertility conditions. This experiment will be repeated during the 2021 field season by MS student Julia Berliner, and prepared for publication. Objective 3: Optimize combinations of cover crops and different compost fertilizers that improve nutrient balance while promoting natural pest suppression. MS student Carly Rae Sharp has been recruited to lead this experiment in the 2022 field season.

Publications

• Type: Journal Articles Status: Published Year Published: 2021 Citation: Blubaugh, C. K., Carpenter-Boggs, L., Reganold, J. P., & Snyder, W. E. (2021). Herbivore-herbivore interactions complicate links between soil fertility and pest resistance. Basic and Applied Ecology, 52, 57-67.