Location: Southeast Watershed Research
2025 Annual Report
Objectives
1. Assess spatial and temporal distribution of the invasive brown marmorated stink bug (BMSB) and whitefly species and their natural enemies relative to environmental and ecological factors in cropping systems and on host plants in surrounding natural areas and field borders and develop a model that will guide decisions on pest management. [NP304, C3, PS3A, 3B and 3C]
1.A. Determine the spatial and temporal distribution of the whitefly, Bemisia tabaci, relative to environmental factors within cropping systems and nearby non-crop hosts in field borders and adjacent natural areas.
1.B. Determine the suitability of treatments with low risk to beneficial insects such selective insect growth regulator insecticides, predatory mites, and biochemical insecticides, to manage the whitefly, Bemisia tabaci.
2. Evaluate parasitism and predation of BMSB and indigenous stink bugs by parasitoids and predators in crop and non-crop habitats. [NP304, C3, PS3A, 3B and 3C]
2.A. Assess parasitism and predation of BMSB and indigenous stink bugs by parasitoids and predators in orchard, vineyard, vegetable, and row crop farmscapes and non-crop hosts in nearby woodlands in the southeastern USA.
2.B. Develop floral habitat to enhance biological control of BMSB and indigenous stink bugs in farmscapes.
3. Develop optimal native wildflower habitat and other floral resources near crop fields for provisioning of resources and refuge sites that increase pollinator abundance, diversity, and pollination of nearby crops, such as initially in cotton and peanut, with potential applications to other pollinator-dependent crops. [NP304, C3, PS3A, 3B and 3C]
3.A. Determine the abundance and diversity of wild bee pollinators utilizing mixed wildflowers, cover crops, cropping systems and field borders, and naturally occurring areas to determine which species is utilizing which floral resource.
4. Improve current and evaluate novel weed management techniques for traditional and organic row, vegetable, and perennial cropping systems produced throughout the southeastern United States.
4.A. Determine if applications of various organic herbicides can provide economic weed control.
4.B. Evaluate interactions between prohexadione calcium and various postemergence herbicides when applied as a tank-mixture.
5. Develop a better understanding of the influence edaphic and environmental factors have on the fate of chemical and non-chemical weed control practices to improve crop and ecological safety while maintaining grower profitability and sustainability.
5.A. Determine the thermal stability and activation energy of various organic herbicides in aqueous solution.
5.B. Quantify the impact drying time has on the movement of herbicides applied over-the-top of mulch covered vegetable beds.
5.C. Assess the potential use of an organic soil amendment for reducing residual herbicide injury to Brassica carinata.
Approach
The spatial and temporal distribution of the whitefly, Bemisia tabaci, and its natural enemies relative to environmental factors will be assessed in cropping systems (row; corn, cotton, peanut, soybean, and vegetable; squash, pepper, eggplant, etc. crops), and on host plants in borders and natural areas. Treatments of low risk to beneficial insects (2 insect growth regulators, 4 species of predatory mites, and 2 biochemical insecticides) will be evaluated for their suitability to control whitefly outbreaks. Also, the spatiotemporal patterns of indigenous stink bugs and the invasive brown marmorated stink bug, Halyomorpha halys, will be assessed in 2-3 orchard, row crop, and non-crop habitats. Sampling will be conducted using whole plant and drop cloth samples and stink bug traps. Evaluation of parasitism and predation of stink bug eggs will be assessed using natural and sentinel egg masses in crop and non-crop hosts in 2-3 blueberry, apple, peach, and pecan orchards, 2-3 grape vineyards, 2-3 vegetable farms, and 2-3 row crop farms. Abundance, diversity, and potential for crop pollination by wild bee pollinators will be assessed. Sampling will be conducted using blue vane bee traps and sweep netting in wildflowers, cover crops, crops, field borders, and natural areas. Species of bees will be identified. Metabarcoding will be used on pollen samples collected from each species to determine which species is utilizing which floral resource. The potential for utilizing organic herbicides in economical weed management programs will be assessed in various runner-type peanut cultivars and 6-8 common and troublesome weed species in greenhouse and field experiments. Tank-mixtures of prohexadione calcium (plant growth regulator) and 2-4 postemergence herbicides will be evaluated in 2-3 runner-type peanut cultivars and 6-8 weed species in greenhouse and field experiments. The influence of edaphic and environmental factors on chemical and organic weed control products will be assessed on 8-10 herbicides in row, specialty, and non-crop areas.
Progress Report
This is the final report for this project which will terminate in November 2025.
Substantial results were realized over the 5 years of the project. Under Objective 1, research on assessing spatial and temporal distribution of the invasive brown marmorated stink bug (BMSB), Halyomorpha halys, in pecan orchards and row crops (i.e., corn, cotton, and soybean) and non-crop hosts in nearby woodlands was completed (Sub-objective 1.C). We found that BMSB is an established pest within these agricultural systems and non-crop host plants play an important role in maintaining populations of BMSB in surrounding habitat. Also, high-density aggregations of this pest were identified so targeted pest management strategies can be developed. We also determined that the timing of stink bug aggregations reflects the life cycle of corn, cotton, and peanut. For growers, this means that pest management strategies for stink bugs may require a farmscape-based management approach that accounts for movement of BMSB into agricultural fields from surrounding habitat.
A field and laboratory study to determine the suitability of pest treatments with low risk to beneficial insects such selective insect growth regulator insecticides, predatory mites, and biochemical insecticides, to manage the whitefly, Bemisia tabaci, was completed (Sub-objective 1.B). We found that EcoVenger®, was the most effective against all life stages of whitefly. In the laboratory, insect growth regulators (IGRs) were found to be most effective against early instars with little to no control at later instar stages of development. Predatory mites in field plots led to a decrease in whitefly eggs in all predatory mite treatments. This experiment demonstrated to stakeholders that whitefly control can be achieved with reduced risk treatments.
Progress was made in determining the spatial and temporal distribution of the whitefly relative to environmental factors (i.e., soil moisture, irrigation, precipitation, natural enemies present, distance from the field edge, wind speed and direction, temperature, humidity, and plant stress) within cropping systems and nearby non-crop hosts in field borders and adjacent natural areas (Sub-objective 1.A.). However, the project was not completed due to the scientist resigning during fiscal year 2025.
For Objective 2, field studies to assess biological control of lab-reared and naturally-laid BMSB and southern green stink bug (SGSB), Nezara viridula, eggs by predators and parasites in orchard, vineyard, vegetable, and row crop farmscapes and nearby hosts in woodlands were completed (Sub-objective 2.A). In the initial study, we found that parasitism of lab-reared stink bug egg masses was higher when the eggs were frozen or refrigerated egg compared to fresh eggs and generally higher for naturally-laid compared to lab-reared eggs. We concluded that collecting natural egg masses is the best methodology for field assessment of parasitism of stink bug egg masses; however, if natural egg masses are not easily available, deploying sentinel eggs is a good alternative. Then in a row crop farmscape consisting of corn, cotton, and soybean, we found that parasitism of BMSB egg masses was 54.3% while 74.2% for SGSB egg masses. For growers, this means that conservation biological control has the potential to enhance parasitism of stink bugs in agroecosystems.
Also, for this objective, a field study to determine if incorporation of an understory of crimson clover in pecan orchards increases parasitism of BMSB in the orchards was completed (Sub-objective 2.B). Five native stink bug egg parasitoid species emerged from the BMSB egg masses deployed in the pecan orchards. Overall, the rate of parasitism of BMSB sentinel egg masses was higher in orchards with crimson clover compared to those without this understory and was higher in the canopy of the trees compared to the ground suggesting that crimson clover improves biological control of BMSB in pecan orchards. For growers, planting crimson clover in pecan orchards can be a simple, sustainable approach to control BMSB.
Significant progress was made on determining the abundance and diversity of wild bee pollinators utilizing mixed wildflower, cover crop, crop, and field borders habitats (Sub-objective 3.A). The field studies have been done; we are awaiting the bioinformatics results from metabarcoding of pollen on bees collected during the study. Identification of pollen on the bees will be used as a measure of the bee species foraging history.
Field research to determine the feasibility of using various organic herbicides in runner-type peanut cultivars was completed at the beginning of 2025 and the companion greenhouse study, which focuses on amount of weed control provided by the organic herbicides, is currently in the third year of completion (Objective 4.A). The third year of the field study to evaluate interactions between prohexadione calcium and various postemergence herbicides is currently underway and will be completed in early fall 2025. The companion greenhouse study is in the second year of completion due to previous poor seed quality of various weed species, with this iteration and the third iteration being completed Summer 2025 (Objective 4.B). The identification of organic herbicides that can be used on runner-type peanut that provide economic weed control without causing reductions in pod yield is crucial for growers, given the high cost per application and extremely limited options currently available.
Research continued on the study to determine the thermal stability of various organic herbicides, with the final run currently being completed. Previous runs of this study could not be completed due to analytical equipment failure; however, the equipment has been replaced and is fully functional (Objective 5.A). Given the high costs associated with organic herbicide applications, the ability to tailor water temperature to each specific compound can allow growers to maximize control across weed species.
The second and third field runs are currently being completed to quantify the impact drying time has on the movement of herbicides applied over-the-top of mulch covered vegetable beds and samples will be fully analyzed by Fall 2025 (Objective 5.B). Understanding the movement of herbicide into the transplant hole can be used to reevaluate current labels and recommendations, potentially creating optimized weed control programs for growers.
The final year of the field trial to assess the potential use of an organic soil amendment for reducing residual herbicide injury to susceptible crops was completed in early 2025 (Objective 5.C). The high residue biomass produced by Brassica carinata, coupled with the ability to use poultry litter as a fertilizer and soil amendment, warrants further evaluation to find the best-fit for this winter cover crop.
Accomplishments
1. Parasitism of the invasive brown marmorated stink bug (BMSB) by an adult parasitoid of this pest in cropping systems. ARS researchers at Tifton, Georgia believe the native southern green stink bug and invasive brown marmorated stink bug are economic pests in corn, cotton, and soybean throughout the southeastern United States. The feather-legged fly parasitizes and kills adult southern green stink bugs. A fly maggot enters the body of the stink bug after hatching from an egg on the body of a stink bug. Eventually as the immature fly develops over time, the stink bug is killed. Little is known regarding parasitism of brown marmorated stink bugs by this fly in crops where they occur together. Thus, our main objective was to evaluate parasitism of southern green stink and brown marmorated adults by this fly in corn, cotton, and soybean from 2019 – 2022. Overall, parasitism was higher for the southern green stink bug compared to the brown marmorated stink bug and higher in corn and cotton compared to soybean. Highest mortality for fly immatures occurred for those that died in eggs (42%). Emergence of a new fly adult occurred more often when greater than one egg was deposited on a stink bug adult. We conclude that this fly prefers the southern green stink as a host but readily parasitizes the brown marmorated stink bug in field crops. Therefore, providing food in the form of nectar of flowering plants to the fly could help in managing both stink bug pests.
2. Use of poultry litter to reduce residual herbicide injury to Brassica carinata. ARS researchers at Tifton, Georgia suggest damage to Brassica carinata from residual herbicides is a significant concern for growers looking to incorporate it into their crop rotations with peanut, cotton, and corn. Because microbial degradation is the primary breakdown pathway for most residual herbicides, field experiments were conducted to assess whether applying poultry litter as a soil amendment could enhance and accelerate herbicide degradation. Results showed no interaction between poultry litter application rate and residual herbicide effects on Brassica carinata biomass. Among the herbicides tested, only fomesafen led to a biomass reduction compared to the untreated control when applied alongside any field rate of poultry litter. Given the substantial biomass produced by Brassica carinata, further research is needed to determine optimal management practices for its use as a winter cover crop in the Southeastern U.S.
3. Repeated applications of organic herbicides in peanut. Management of weeds in organic peanut is challenging and requires a combination of methods rather than relying on chemical control. There are an extremely limited number of organic herbicides available for use that allows producers to maintain their organic certification and most still need to be evaluated for their effectiveness in runner-type peanut. This study was conducted by ARS researchers at Tifton, Georgia with field and greenhouse studies to determine the feasibility of achieving economic weed control without reducing peanut yield. Results indicate that while varying levels of visual injury was observed, all of the evaluated runner-type peanut cultivars were able to quickly recover and injury did not translate into yield loss. There were varying trends in pod yield across herbicides and cultivars, but trends were inconsistent among treatments. High input prices of these products warrants continued evaluation to ensure best-use in organic peanut.
4. Use of prohexadione calcium and postemergence herbicide tank-mixtures in peanut. ARS researchers at Tifton, Georgia believe excessive peanut vine growth can create a favorable environment for disease development under the canopy. Applying a plant growth regulator in peanut production can help manage vine growth, improve yield, and potentially enhance overall net returns. With rising input costs, tank-mixing these products with other agrochemicals offers a cost-effective alternative to sequential applications, reducing both expenses and application time. This study aims to evaluate the effects of tank-mixing prohexadione calcium with commonly used postemergence herbicides on peanut injury and weed control. The field study assessed visual injury levels and yield impacts, while the greenhouse study examined species-specific weed control efficacy. Preliminary findings indicate that these tank mixtures can be applied postemergence without negatively affecting yield. However, greenhouse results showed variable weed control depending on species, highlighting the need for further research to confirm these trends.
Review Publications
Tillman, P.G., Grabarczyk, E.E. 2025. Success of parasitism of Nezara viridula and Halyomorpha halys (Hemiptera: Pentatomidae) by Trichopoda pennipes (Diptera: Tachinidae) in the southeastern United States. Journal of Insect Science. 3. https://doi.org/10.1093/jisesa/ieaf046.
Coffin, A.W., Pisani, O., Pisarello, K., Porter, K.M., Bosch, D.D., Strickland, T.C. 2024. The LTAR Croplands Common Experiment at the Gulf Atlantic Coastal Plain. Journal of Environmental Quality. 53(6):869-879. https://doi.org/10.1002/jeq2.20645.
Olson, D.M., Gibbs, J., Schmidt, J. 2021. Wild bee pollinators foraging in peanut and cotton adjacent to native wildflower strips. Florida Entomologist. 104(3):165-172. https://doi.org/10.1653/024.104.0304.
Tillman, P.G., Cottrell, T.E., Kesheimer, K.A., Grabarczyk, E.E. 2024. Assessment of sugarberry as a host tree of Halyomorpha halys (Hemiptera: Pentatomidae) in southeastern US agroecosystems. Florida Entomologist. 107(1):2024-0054. https://doi.org/10.1515/ aent-2024-0054.
Grabarczyk, E.E., Tillman, P.G., Querejeta, M., Schmidt, J.M. 2025. Honey, what's for dinner? Dietary overlap and size dimorphism between female and male Joro spiders (Trichonephila clavata). Integrative Zoology. 0:1-10. https://doi.org/10.1111/1749-4877.12947.