Final Report for GNE12-044
Many studies have noted the significance of reduced tillage and increased crop residue to the generalist predator community in agroecosystems. However, many of these studies have assumed that reducing tillage and increasing organic matter at the soil surface will contribute to increased biological control, without actually monitoring any changes to the biocontrol potential (Letourneau and Bothwell 2008). For this project, we thus surveyed the early-season arthropod pest and predator communities in an organic reduced tillage agroecosystem to better understand the effects of these practices to the arthropod assemblages. In the project system, corn and soybeans were no-till planted at three different dates into a heavy mulch layer created by managing a winter cover crop with a roller-crimper. We then assessed the ground-dwelling arthropod community using pitfall traps and visual assessments, and conducted predation assays to estimate the potential for predation on arthropod pests. We determined that the date of cover crop control, as well as the type of cover crop into which the cash crop is planted, may affect the arthropod community in this agroecosystem. The cover crop mat may provide additional resources for the generalist predator community, thereby assuring their retention in the field and later benefit to organic growers for managing arthropod pests. This project provides additional information regarding potential pest control benefits of cover cropping and the retention of crop residues at the soil surface.
Letourneau, D.K. and Bothwell, S.G. 2008. Comparison of organic and conventional farms: challenging ecologists to make biodiversity functional. Frontiers in Ecology 6: 430-438.
Further, reduced tillage and cover crops provide many tangible benefits to both conventional and organic growers, with one potential benefit being the conservation of generalist arthropod predators. Insect predators, for example, ground beetles and spiders, eat a variety of prey organisms. They prefer a complex habitat and their presence can supplement control of plant-feeding pests (Lang et al. 1999; Schmidt and Rypstra 2010). However, the specific contributions of reduced tillage and cover cropping to conserving arthropod predators is not well understood in organic feed-grain production systems in the Mid-Atlantic. This project will demonstrate the effects of high residue, organic reduced tillage cropping systems on the abundance, community composition, and pest-suppression activity of predators. As a result, we will increase the information available to farmers to support the adoption of these practices and their contributions to farm sustainability.
Some early-season pests, including seedcorn maggot (Delia platura), are drawn to the high residue environment created by cover crops and reduced tillage (Hammond 1991; Mischler et al. 2010). However, by appropriately timing planting dates of cash crops, farmers may avoid potential early-season pest outbreaks. In addition to implementing no-till planting of cash crops (corn, soybean and wheat) into rolled cover crops, we will evaluate three different cash crop planting dates for their impact on beneficial arthropod populations and activity. By monitoring early-season pest populations, we can determine whether or not the high-residue environment contributes to the abundance and early-season crop damage by these insect pests, and if the predator community is able to prevent or reduce the potential damaging effects of early-season pests.
My proposed project will take advantage of and bring a new area of research to a larger, on-going project that examines weed management, soil quality, energy use, and economic benefits and challenges of an organic reduced tillage cropping system. My preliminary assessments of the ground-dwelling arthropod populations indicate that generalist predators are abundant in the cash crops planted into the rolled cover crop residue. However, the presence of these organisms does not necessarily indicate their success in preying upon significant pests within the cash crops. Some generalist predators may alternate between non-pest prey and plant-feeding pests, depending on the presence of each of these groups and timing during the season (Kuusk and Ekbom 2010; Birkhofer et al. 2011). Similarly, the presence of multiple predators in the same location may alter the efficacy of these predators in controlling pests due to intraguild predation, in which predators consume each other in addition to pests (Birkhofer et al. 2011). Further characterization of the predator community in reduced tillage, high residue systems is necessary to fully understand their functional role, and to better understand the habitat components that will contribute to enhancing their numbers and benefits to pest management. Many questions remain related to timing the termination of cover crops and the planting of cash crops to maximize their effects on insect and weed management, crop yield, and profitability, which are ongoing research priorities of the larger project to which my project will contribute. Examinations of the predator-prey interactions is not currently an ongoing objective of the project, and leveraging the same research site to address other aspects of the sustainability of this production system could have great implications for organic and conventional growers.
By providing growers with more information regarding the beneficial and pest arthropod communities in an organic, high residue reduced tillage crop production system, this project will provide greater support for the adoption of these practices. Specifically, this project will address the following research priorities addressing whole-farm sustainability:
- The reduction of environmental and health risks in agriculture by further supporting agriculture with no chemical inputs
- Improved productivity through increased soil quality and the reduction of on-farm costs associated with equipment energy use
- Improving conservation of soil, the improvement of water quality, and the protection of natural resources; the enhancement of employment in rural areas; and therefore, improvement of quality of life for farmers, their employees, and the farm community.
Birkhofer, K., Wolters, V., and Diekötter, T. 2011. Density-dependent and -independent effects on the joint use of space by predators and prey in terrestrial arthropod food-webs. Oikos 120: 1705-1711.
Bond, W., A.C. Grundy. 2001. Non-chemical weed management in organic farming systems. Weed Res. 41: 383-405.
CTIC (Conservation Technology Information Center). 2002. Tillage type definitions. West Lafayette, IN: Conservation Technology Information Center, Purdue University.
Hammond, R.B. 1991. Seedcorn maggot (Diptera: Anthomyiidae) populations on Ohio soybean. Journal of the Kansas Entomological Society 64: 216-220.
Jackson, L. E., Ramirez, I., Yokota, R., Fennimore, S. A., Koike, S. T., Henderson, D. M., Chaney, W. E., Calderón, F. J., and Klonsky, K. 2003. On-farm assessment of organic matter and tillage management on vegetable yield, soil, weeds, pests, and economics in California. Agriculture, Ecosystems and Environment 103: 443-463.
Kuusk, A. and Ekbom, B. 2010. Lycosid spiders and alternative food: Feeding behavior and implications for biological control. Biological Control 55: 20-26.
Lang, A., Filser, J., and Henschel, J.R. 1999. Predation by ground beetles and wolf spiders on herbivorous insects in a maize crop. Agriculture, Ecosystems & Environment 72: 189-199.
Mirsky, S.B., Ryan, Curran, W.S., Mortensen, D.M., Ryan, M.R., and Shumway, D.L. 2011. Timing of cover-crop management effects on weed suppression in a no-till planted soybean using a roller-crimper. Weed Science 59: 380-389.
Mischler, R., Duiker, S.W., Curran, W.S., and Wilson, D. 2010. Hairy vetch management for no-till organic corn production. Agronomy Journal 102: 355 – 362.
Schmidt, J.M. and Rypstra, A.L. 2010. Opportunistic predator prefers habitat complexity that exposes prey while reducing cannibalism and intraguild encounters. Oecologia 164: 899-910.
The increased habitat complexity associated with cover cropping and reduced tillage can be attractive to a variety of arthropods. It is therefore important to understand what arthropods are in the field to know how they affect pest and beneficial arthropod communities.
Objective 2: Determine the effect of three cover crop management and cash crop planting dates on the arthropods in a reduced-tillage organic feed grain rotation.
The presence and life stage of pest and beneficial arthropods are affected by several environmental factors, including amount and condition of cover crop residue, weather, and host availability and life stage. Therefore, timing of cover crop management and cash crop planting will affect potential crop damage by early season insect pests. By characterizing the ground-dwelling arthropod community, we can determine if predators are present at the same time as potential early-season pests, and which cover crop management and planting dates can maximize the level of predation on pest populations.
Objective 3: Determine the relationship between the arthropod community and early season crop damage and plant population in a reduced-tillage organic feed grain rotation.
The presence of predators at the same time as pests may only be beneficial if the predators are contributing to control of the pests. By measuring crop damage in relation to pest and predator populations, we will determine what, if any, effect the predator community may have on preventing crop damage.
Objective 4: Determine the potential impact of generalist insect predators on populations of early-season pests associated with a reduced-tillage organic feed grain rotation.
Knowing that the predators and pests are present at the same time will contribute to the knowledge that these predators are at least available to prey upon insect pests. In-field predation assays will help estimate the potential for predators to actually reduce pest populations.
Objective 5: Provide opportunities for the exchange of information with organic growers about this production system and its effects on beneficial and pest arthropods.
By working with organic growers to disseminate the information about this project and evaluate their perceptions, we can determine benefits and challenges to grower adoption of organic reduced tillage crop production, and determine additional information needed to gain grower acceptance and adoption.
The work for this project was conducted at the Russell E. Larson Agricultural Research Center, located in Centre County, Pennsylvania. The total area of the experimental site is approximately 4 hectares, all of which were in the final two years of the transition to certified organic land according to United States Department of Agriculture National Organic Program standards during the project term. Soils at the site are representative of the Hagerstown Soil Series according to the United States Department of Agriculture, Natural Resources Conservation Service soil classification system, a silt loam classified as prime farmland (Soil Survey Staff, 2014). The project leveraged the existence of a large-scale cropping systems experiment designed to test the effect of multiple agronomic practices—including cash crop variety, planting date, and high residue cultivation—on insect and weed pest dynamics.
The full project consisted of four blocks of a full entry design with three cash crops—corn (Zea mays L.), soybean (Glycine max (L.) Merr.), and wheat (Triticum aestivum L.)—planted in every growing season during the years 2011 to 2013. Cash crops are rotated annually with a cover crop such that each cash crop is present in every year of the experiment, with a complete rotation as follows: Corn, cereal rye (Secale cereale), soybean, wheat, and hairy vetch (Vicia villosa) planted together with triticale (× Triticosecale Wittmack). Prior or at the time of planting of corn or soybean, cover crops are managed by rolling, and corn and soybean are no-till planted into the mat of residue created by the rolled cover crop. Winter wheat is planted into a plot that has been moldboard plowed, and is then harvested the following summer. The field work for this project was conducted during the 2013 growing season, when the site had already experienced two full years of the cropping cycle.
Characterizing the ground-dwelling arthropod community (Objectives 1, 2 and 3)
We employed a series of pitfall traps at each site in each of the cash crops prior and after cash crop planting, during the months of May through July. Pitfall traps are a measure of both activity, as well as density of arthropods, however, this does not translate to a specific density measure as it is not possible to relate the captures to a specific unit of area. But, pitfall traps do give us valuable information about the most abundant groups present and active in any given treatment. The traps consisted of a one liter plastic deli container buried level with the soil surface. At the time of arthropod trapping, a plastic specimen cup filled with 30-mL ethylene glycol, used to kill and preserve the insects, was placed inside of a deli container. A funnel resting in the specimen cup helped to facilitate insect movement into the ethylene glycol. Traps remained open in the field for 72 hours, after which the samples were brought to a laboratory. All arthropods were removed from the trap, preserved, counted and identified to at least order, with some groups further identified to family and species, and assigned to a specific trophic group (for example, herbivore, predator, or decomposer). For all corn and soybean planting dates, trapping was conducted once prior to cover crop management by rolling, and once approximately one week after cash crop emergence. Additionally, we conducted a single trapping event approximately one month prior to wheat harvest. We also measured various environmental variables at the time of pitfall trapping, including the depth of crop residues and the height of any standing crop.
Identifying relationships between the arthropod community and early-season plant damage (Objective 3)
In addition to data collected via pitfall trapping, to meet this objective, we assessed specific herbivorous arthropod populations on the soil surface and conducted early-season crop population assessments. To assess herbivorous arthropods, we visually inspected the soil surface for lepidopteran larvae (caterpillars) within a 0.813 square meter area. Pests were identified in the field to species or family, or captured and taken to the laboratory for identification when not possible to do so in the field. We assessed early-season crop populations and damage in corn and soybeans only, and did so by counting the total number of seedlings, and total number of seedlings with stippling (feeding conducted by insects with piercing/sucking mouthparts, such as Hemipterans), chewing, slug damage, and cutting (plant stems that had been completely chewed off at the base where it emerges from the soil) were counted to determine the proportion of plants with damage by herbivorous arthropods (and molluscs).
Determining the biocontrol potential of generalist arthropod predators (Objective 4)
To meet this objective, we employed non-targeted traps (sentinel traps), baited with live waxworm larvae (Galleria mellonella) in each treatment plot. The traps consisted of a cardboard substrate baited with five lab-reared caterpillars affixed with hem-tape. The cardboard substrate was placed on the ground, and surrounded by a cylinder of 19-gauge hardware cloth to exclude larger animals. The traps were placed in close proximity to pitfall traps, and left in the field for 24 hours prior to pitfall trapping. After 24 hours, the cards were collected and the number of damaged and undamaged caterpillars counted to determine the proportion of predated waxworms. Trapping was repeated in the same manner in the 24 hours directly after pitfall trapping. The cards were brought to the laboratory, frozen, and then each caterpillar was visually inspected feeding damage by arthropod predators. The proportion of damaged caterpillars per plot provides information about the local biocontrol potential for that treatment.
Soil Survey Staff, N. U. (2014, June 9). Web Soil Survey. Retrieved from Centre County Soil Survey: http://websoilsurvey.nrcs.usda.gov/
Generally, we anticipated treatment differences in the abundance and diversity of different arthropod groups, primarily because of arthropod and crop physiology. Arthropods did respond to timing of the various practices in the system, as well as to aspects such as crop and cover crop identity as well. Prior to cover crop management, the predatory arthropods captured with the highest activity-densities varied between the corn, soybean and wheat treatments (Figure 1). The presence of these predators early in the season in the standing cover crops present prior to corn and soybean (hairy vetch and triticale prior to corn, and rye prior to soybean) are important for the potential for pest control purposes later in the same season for the cash crops, while in wheat, the presence of predators is more important from a legacy standpoint. That is, any predators that are present in wheat at the time captured may play an important role in stabilizing predator activity later in the crop rotation (in this system, the hairy vetch and triticale cover crop follows wheat, after which corn is planted). Many of the most abundant groups—spiders and harvestmen in corn, rove beetles in soybean and wheat—have been cited as important pest control agents in various agroecosystems (Lang et al. 1999; Pfannenstiel and Yeargan 2002; Maloney et al. 2003; Brunke et al. 2014).
The total activity-density of predatory and herbivorous arthropods varied by date, as anticipated (Figure 2). The activity-density of the total predator assemblage was consistently higher than that of the herbivores for all crops and sampling dates, however, it appears that there is a peak in predator activity around Julian Day 154 (corresponding with a calendar date of June 3, 2013). Generally, predator activity-density trends towards an increase in the soybean treatments with date, while activity peaks in corn treatments and then remains relatively stable for the dates presented. In all treatments, composition of the community varies with time (data not shown), as expected based on the different physiological requirements of arthropods. However, the variation in community composition, and consistently high numbers of generalist predators in this system, could indicate that predators are reliably present to contribute to biocontrol.
A similar peak as that in predator activity-density is present in the feeding behavior of these predators, as indicated by the proportion of sentinel waxworms predated in the field (Figure 3). Predation in the corn treatments (the standing hairy vetch and triticale cover crop early in the season) was fairly high, with between 30 and 100% of waxworms exhibiting feeding damage in the standing cover crop. These values remain high after corn has been planted, suggesting that pest control agents may be present amongst the ground-dwelling predator assemblage.
We are still in the early-stages of processing data for this project, therefore all results presented herein are preliminary. While we were previously aware that generalist arthropod predators were present in the field at some level, the data collected for this project provides us with new information regarding the potential for these predators to serve as pest control agents. As we continue to analyze data, we can finalize the results regarding the impact of the predators at this field site, as well as relate this information to plant damage and yield. Likewise, it is rare for information to be gathered on the feeding behavior of the predator community, and we may be able to draw some inferences from our data regarding the habitat features (e.g. density of cover crop mat) that may be driving predatory arthropod activity.
Brunke, A. J., Bahlai, C. A., Klimaszewski, J., & Hallet, R. H. 2014. Rove beetles (Coleoptera: Staphylinidae) in Ontario, Canada soybean agroecosystems: Assemblage diversity, composition, seasonality, and habitat use. Biodiversity & Evolution 146: 652-670.
Lang, A., Filser, J., and Henschel, J.R. 1999. Predation by ground beetles and wolf spiders on herbivorous insects in a maize crop. Agriculture, Ecosystems & Environment 72: 189-199.
Maloney, D., Drummond, F. A., & Alford, R. 2003. Spider predation in agroecosystems: Can spiders effectively control prest populations? University of Maine, Biological Sciences. Orono, ME: Maine Agricultural and Forest Experiment Station.
Pfannenstiel, R. S., & Yeargan, K. V. 2002. Identification and diel activity patterns of predators attacking Helicoverpa zea (Lepidoptera: Noctuidae) eggs in soybean and sweet corn. Environmental Entomology 31: 232-241.
It is widely believed that generalist arthropod predators may contribute to biocontrol in both organic and conventional agroecosystems. However, empirical evidence regarding the actual potential for these predators to serve as biocontrol agents is limited, especially in organic systems. Additionally, multiple metrics of biodiversity (e.g. the relative abundance of each member of a community as measured by evenness) as they relate to biocontrol are increasingly receiving more attention (Crowder et al. 2010). As we proceed with data analysis, we can provide more information to the existing body of scientific literature regarding various agricultural practices and their effect on the predator and herbivore communities, and the composition, abundance, diversity, of various taxonomic groups. Too, since we conducted our predation assays in the field, we can draw inferences regarding actual field conditions that may drive the biocontrol potential of the predatory groups.
Crowder, D. W., Northfield, T. D., Strand, M. R., & Snyder, W. E. 2010. Organic agriculture promotes evenness and natural pest control. Nature 466: 109-113.
Education & Outreach Activities and Participation Summary
All of the data collected for this project, as well as the extension fact sheet will become part of the doctoral dissertation of Ariel Rivers. At least two publications are also in preparation for submittal to nationally recognized, peer reviewed journals: One presenting the results related to the entire ground-dwelling arthropod community, and one focused specifically on ground beetles. Over the course of this project, multiple posters and presentations were given at research expositions, outreach events, and project meetings: At the project Advisory Board meeting in December 2012; the Penn State Sustainable Agriculture Triad Research Symposium in 2013 and 2014; and the Entomology Student Colloquium in June 2014. Additionally, an extension fact sheet discussing the biocontrol potential of ground-dwelling generalist predators in high residue agroecosystems is currently in preparation, and we have plans to present the project results at the 2015 Penn State Sustainable Agriculture Triad Research Symposium. All dissertation chapters and publications will be made available to SARE as they are completed.
Aspects of the system studied for this project have great potential for application in organic agroecosystems of the Mid-Atlantic. Further research is necessary to explore the benefits to pest control of various cover crops, i.e. in their potential for retaining ground-dwelling generalist predators in the field and ideal cover crops for maximizing biocontrol potential. Additionally, specific aspects of the system, such as timing of cover crop control and planting in a high residue environment are worthy of further exploration prior to wide scale recommendation to farmers.
Areas needing additional study
As mentioned above, there are aspects of the system that need to be further explored in order to maximize the agroecosystem studied for this project. Dr. Mary Barbercheck will continue research in the area of organic, reduced-tillage cropping systems, and has already received funding to continue work in this area at Penn State. Additionally, the ground-dwelling arthropods captured within the pitfall traps may not be representative of the entire community contributing to pest control, as indicated by sentinel trapping. A refined methodology for studying the feeding behavior of the predator community is necessary to better understand the relationship between aspects of the cropping system (e.g., cover crops), and the most important pest control agents. The type of cover crop mulch itself seems to play a significant role in determining the abundance and identify of predatory arthropods in the field, and the mechanisms behind this warrant further investigation as well.