Progress report for GS21-240
Southern crop producers are shifting more and more to sustainable practices to increase conservation efforts. Whether it be the planting of shelterbelts for erosion control or the use of cover crops to promote better soil health, growers have several options to improve farm sustainability. Conservation strategies can be developed through the aid of programs like the Conservation Stewardship Program, whose main goal is to provide farmers the tools to successfully apply these conservation tactics on their farms. Several of these environmental manipulations may also support more stable natural enemy abundances, but a better understanding of whether the tactics provided by the Conservation Stewardship Program effectively increase natural enemy abundance is still needed. Do plantings like hedgerows enhance natural enemy or pest populations or both? Collaboration with Louisiana soybean producers that are currently enrolled in the Conservation Stewardship Program to investigate the effects of hedgerow plantings on both natural enemy and pest populations will take place within this study. Additionally, stink bug pests and three natural enemy groups, Geocoris spp., Reduviidae, and Araneae, will be targeted to track movement and verify whether migration into adjacent soybean occurs. The main goal of this proposed study is to aid in the development of more sustainable management strategies by determining if Conservation Stewardship Plantings effectively conserve natural enemies or if they provide a bridge for pests into adjacent soybean.
Objective 1. Monitor abundance of arthropod natural enemies and pests within Conservation Stewardship plantings during the growing season.
Objective 2. Determine movement of arthropods from Conservation Stewardship plantings into adjacent crop using a mark and capture technique
To evaluate how conservation strategies employed by Louisiana producers enrolled in the Conservation Stewardship Program affect natural enemy and pest populations, monitoring of arthropod communities within Stewardship plantings adjacent to soybean will take place. Because recommended Stewardship plantings vary on a farm-to-farm basis, assessments will focus strictly on farms with similar deployed tactics. The Conservation Stewardship strategy we will focus on is the use of hedgerow plantings. Collaboration with LSU AgCenter Extension agent, Dennis Burns and NRCS agent, Steven Nipper, will aid in the locating of willing participants. Farmscapes within Tensas Parish, LA and Franklin Parish, LA will be selected for this study, both on producer farms and at the Macon Ridge Research Center, Winnsboro, LA (Franklin Parish) and the Northeast Research Center, St. Joseph, LA (Tensas Parish). Within each parish, one on-site university planting and one off-site collaboration with a local producer will sampled for a total of four sites. Sampling will take place across Year 1 and 2 to account for any variation year to year.
Experimental design will follow that of a complete block design with each site being treated as a block. Within each site, set-up will consist of hedgerow plantings adjacent to soybean. The Conservation Stewardship Program prescribes a ratio of 0.2 ha of conservation cover for every 16.2 ha of crop cover. Each hedgerow planting will be arranged into four equal sized plots. Each plot will be sampled at each time point to account for spatial variation within the hedgerow planting. Hedgerow plantings are generally comprised of a mix of native perennial shrubs, forbes, and grasses. Each plot will contain a mix of all plant types and sampling methods will be adjusted for the type of plants sampled. Perennial shrubs will be aerial sampled, while grasses and forbes will be sweep and aerial sampled.
Foliage residing and aerial arthropods will be sampled starting April 1st and then subsequently sampled every 21 days for a duration of 18 weeks. Foliage samples will consist of sweeping within a single 0.9 m diameter circle (hoop) with a sweep net (0.38 m diameter) for each plot at each site (a total of 16 sweep samples per time point). Sampled area will be randomly selected by tossing a hoop into plot. Aerial arthropod populations will be sampled twice within each plot using yellow sticky cards. Cards will be placed above the plants on a 1.2 m bamboo pole, while cards will be placed above shrubs using wire holders. All cards will be changed after 48 hours. Samples will be returned to laboratory for further identification to the lowest possible taxonomic level.
A generalized linear mixed model approach will be used for statistical analysis with R version 3.6.0 (R Core Team 2019). The sampling time point and year will be treated as fixed effects. Farm site will be treated as a random effect. A repeated measures statement for sampling time point being measured over farm site will be included as a random effect. Each plot is considered a sampling unit for their representative hedgerow planting. Each sampling method (aerial and foliage) will be analyzed separately. The response variable for this model will be the number of individuals collected for select arthropod groups.
To assess whether recommended Conservation Stewardship Program plantings are a source of select arthropods to soybean, the application of a protein-based mark and capture technique will used to observe pest movement. Mark and capture will take place within the same farms as Objective 1. As stated in Objective 1, the Stewardship planting evaluation will address hedgerow plantings. The targeted pests for this objective will focus on the community of stink bugs known to be pests of Louisiana soybean. For natural enemies, focus will be on big-eyed bugs, Geocoris spp., assassin bugs, Reduviidae, and spiders, Araneae, as a preliminary study has shown these two groups to be the most abundant (Lee et al., in prep.) Sampling will take place over two field seasons to address year to year variation.
Mark and capture protocols will follow that of Bastola et al. (2018b). The marker system will use chicken egg albumin (egg whites) as a protein-based marker that can be subsequently identified through ELISA assays in the laboratory. Marking will be deployed using a 20% egg white solution that will be sprayed along ground and foliage of Stewardship plantings. Applications will take place at two time points: early season (vegetative to initial flowering stage in adjacent soybean) and late season (pod-fill stage in adjacent soybean). Two separate sections of 2 m x 200 m along hedgerow planting edge will be sprayed with egg white solution, one for each time point. Two days after application, sampling will take place along five evenly spaced (50 m of separation) transect lines directed into soybean away from the center of sprayed section edge. Distances to be sampled are 0 m (field edge), 5m, 10 m, and 20 m from the sprayed area. One set of mark and capture sampling time points (ten transects total) will take place at each farm site, with each farm site being treated as a block.
For each given time point and each sampling location along each transect, a single set of 25 sweeps will be completed. Collected insects will be placed individually into Whirl-PakÓ bags to avoid cross contamination. Bags will be transported back to laboratory and frozen until use for ELISA assays. ELISA assays will follow similar methods as Bastola and Davis (2018b). Additionally, leaf tissue samples from Stewardship plantings will be collected during each arthropod collection date as an internal check to confirm presence of marker.
ELISA assays confirming the presence or absence of protein marker will be analyzed using a binary logistic regression with sampling time point and distance from Stewardship planting as fixed effects. Farm site and year will be treated as random effects. Each species will be analyzed separately.