Progress report for LS22-366
Project Information
The Southeastern U.S. is the second largest peach producing region in the country. However, producing peaches in the southeast is challenging due to the climate favorable for pest and disease development. In addition, orchard soils have low soil organic carbon content, meager soil fertility, and poor soil structure, which inflicts tree stress that negatively impacts pest and disease tolerance and may lead to reduced yields. Current commercial practices do little to improve the soils.
Bacterial diseases intensify from both the favorable climate and stress-induced predisposition to infection. Bacterial spot (caused by Xanthomonas arboricola pv. pruni) and bacterial canker (caused by Pseudomonas syringae pv. syringae) are the two most important bacterial diseases of peach and cause significant direct annual losses - up to $22 million in South Carolina and Georgia alone (estimates from SC/GA Peach Councils). Bacterial spots on peach leaves could lead to severe defoliation, and spots on fruit significantly reduce the marketable yield. Bacterial canker on woody tissues leads to shoot death and tree death. Managing these two diseases is very challenging. There are no cultivars with absolute resistance to either of the two diseases; only a few cultivars are tolerant to bacterial spot and no cultivar has tolerance to bacterial canker. Currently, no chemical control options are available for bacterial canker, and bacterial spot management mainly relies on weekly sprays of copper and antibiotics during the growing season. These chemicals could negatively impact the environment and have led to emergence of copper-tolerant and antibiotic-resistant pathogens, as recently found in SC, indicating an even greater need for new management options.
Our goal is to improve sustainability of the southeastern peach production systems by developing holistic strategies to improve disease management and tree health. In collaboration with peach producers, a multi-disciplinary team of plant pathologists, horticulturist, soil biogeochemist, economist, and entomologist will conduct systems research to: 1) develop sustainable tree spray programs with biopesticides to reduce bacterial diseases; 2) assess sustainable soil management practices and their integration with spray programs on reducing bacterial diseases; 3) evaluate the spray programs and soil practices and their integration on tree health/performance, soil health, and management of other diseases and pests; and 4) evaluate the profitability of the new spray programs and soil practices and develop an enterprise budget for organic peach production. In the first year of the project, some biopesticides have shown promise in managing bacterial spot and bacterial canker in the growing season and/or dormant season, and the soil amendments were found to improve soil functions associated with water retention, microbial activities, and nutrient cycling. We presented our research results to producers and the scientific community and reached out to the underserved producers for needs assessment to increase their equity in the southeast. We expect our findings to benefit the entire production system of peach as well as other stone fruits affected by the same diseases, and to contribute to the long-range improvement of U.S. agriculture.
- Develop sustainable spray programs with biopesticides to reduce bacterial diseases;
- Evaluate biopesticides on bacterial disease development in greenhouse and research field;
- Evaluate biopesticides on bacterial disease development in both conventional and organic peach orchards;
- Assess sustainable soil management practices and their integration with spray programs on reducing bacterial diseases in research orchards;
- Evaluate the impact of various soil management practices on bacterial disease development;
- Evaluate the integrated impact of soil practices and spray programs on bacterial disease development;
- Evaluate the independent spray programs and soil practices and their integration on tree health/performance, soil health, and management of other diseases and pests;
- Evaluate spray programs alone;
- Evaluate soil practices alone;
- Evaluate the integration of spray programs and soil practices;
- Evaluate the profitability of the new spray programs and soil practices and develop an enterprise budget for organic peach production;
- Compare the profitability of the new spray programs and soil practices with conventional and organic growers’ standard programs;
- Develop the first enterprise budget for organic peach production.
Cooperators
Research
Objective 1: Develop sustainable spray programs with biopesticides to reduce bacterial diseases.
Bacterial spot control:
In the 2023 growing season, 18 biopesticide spray treatments were evaluated in the research peach fields for managing bacterial spot on leaves and fruit. Copper (0.1 lb MCE/acre) and untreated control were included as control. The spray treatments were applied every 7-10 days. There were four replicates/trees per treatment. Disease incidence and severity were rated on five shoots per tree for a total of five times. Disease data were analyzed with a generalized linear mixed model in MiniTab.
In the 2023 dormant season, a potted tree trial, two field trials in research peach orchards, and three field trials in commercial orchards were conducted. A total of 12 biopesticides and copper treatments were sprayed three times during the leaf drop period in the potted tree trial and also in the research field trials. Three biopesticides and copper treatments that reduced spring canker in our 2022 dormant season research trial were sprayed three times in three commercial peach orchards. There were four replicates/trees per treatment; untreated control was included. Incidence and severity of spring canker are being recorded from ten randomly selected twigs per tree.
Bacterial canker control: In the 2023 dormant season, we repeated the 2022 potted tree trial using the natural infection method. Peach twigs at the same age were pruned and sprayed with each biopesticide strain, copper, or sterile tap water (control). Then, pruning cuts were exposed to natural infection through rain events and sprayed with the biopesticide/copper treatments two more times. There were four replications/twigs per treatment. The experiment was conducted twice. Lesion length is being measured.
Objective 2: Assess sustainable soil management practices and their integration with spray programs on reducing bacterial diseases in research orchards.
In 2022, we carried out three field trials where the impact of different soil management practices on incidence and severity of bacterial diseases were evaluated: 1) Addition of mulch to a young orchard that previously received composted mulch before planting (incorporated); 2) Addition of mulch (with or without chicken manure) to a mature orchard; and 3) Addition of compost to a young orchard that received compost from food waste before planting (incorporated). The mature orchard (#2) has natural presence of bacterial spot every year, but bacterial spot was spray-inoculated with a local Xap strain (106 cfu/ml) in all the three orchards used in this study (both the matured and young orchards).
In 2023, we maintained the same number of orchards as in 2022. Xap canker was rated in spring. The best biopesticide from the 2022 trials was sprayed on a subset of mature trees from each treatment in orchard # 2. The effect of the soil amendment programs on the bacterial spot incidence and severity was re-evaluated in 2023 but with higher strength/doses of bacterial spot inoculum. Specifically, in May 2023, 5× 107 cfu/ml of a local Xap strain was foliarly applied in all three orchards. Leaf and fruit incidence and severity of bacterial spot was assessed in all orchards; leaf evaluations took place monthly during spring and summer, and fruit evaluations were carried out on samples of 25 fruit/tree harvested three times during harvest season. Fruit was harvested at commercial ripeness. Bacterial spot severity on fruit was evaluated with a visual scale (0-5).
Objective 3: Evaluate the independent spray programs and soil practices and their integration on tree health/performance, soil health, and management of other diseases and pests.
Soil health parameters were measured in soil samples collected twice a year. Soil cores (0-15 cm) were randomly collected with soil corer (5 cm diameter) from replicated research plots. Collected soil cores were sieved (2mm) and stored at 4 °C until use. In the laboratory, soils were quantified for water content by drying the soils at 60 °C until a constant weight was reached. Nitrogen concentrations (NO3- + NH4+) were determined after extracting the soils with 1 M KCl for 1 hour followed by filtration and colorimetric analyses. Organic nitrogen mineralization potentials were estimated by anaerobically incubating soils in dark at room temperature for 7 days, followed by quantifying the changes in NH4+ concentrations. Microbial respiration was estimated by incubating soil samples in dark at room temperature for 24 hours. The CO2 production was quantified and used to calculate the respiration rates. Activities of soil enzymes associated with carbon and nitrogen cycling were measured with fluorescence methods.
Soil moisture, and tree horticultural performance such as gas exchange, tree water status, yield, marketable yield, fruit quality were also measured. Other diseases and pests were monitored in the field trials.
Objective 1: Develop sustainable spray programs with biopesticides to reduce bacterial diseases.
Bacterial spot control: In the field trial of the 2023 growing season, a biopesticide treatment and copper significantly reduced the bacterial spot severity on peach leaves but copper caused significantly more damage (phytotoxicity) on leaves than bacterial spot. The best performing biopesticide is being tested in three commercial peach orchards in the 2024 growing season. The spring canker data from the 2023 dormant season trials are being collected.
Bacterial canker control: The canker data from the 2023 dormant season trials are being collected.
Objective 2: Assess sustainable soil management practices and their integration with spray programs on reducing bacterial diseases in research orchards.
Similar to the results obtained in 2022, the annual topical application of mulch with chicken manure in orchard #2 (known to have yearly natural bacterial spot infection) resulted in lower bacterial spot incidence and severity in leaves when compared with the trees that received mulch only and control (bare soil). Although there was no statistical difference in the bacterial spot incidence and severity on fruit between the three treatments, we observed numerically lower bacterial spot incidence on fruit of the trees that received mulch with chicken manure compared to the fruit of the trees that received mulch only and control treatments.
There was low pressure of bacterial spot in the other two orchards despite the higher strength/doses of Xap inoculum compared to the strength of Xap inoculum applied in 2022. There was no statistical difference in the bacterial spot incidence and severity in leaves and fruit between treatments. However, numerically lower bacterial spot incidence and severity were observed in leaves and fruit of the trees treated with compost incorporation when compared to the control, suggesting that the pre-plant incorporation of compost could improve the overall quality of the marketable fruits and orchards productivity.
Objective 3: Evaluate the independent spray programs and soil practices and their integration on tree health/performance, soil health, and management of other diseases and pests
Regarding the orchards' horticultural performance, young trees receiving pre-plant incorporation of compost had a larger trunk cross-sectional area (TCSA) compared to the control treatment. A similar response trend was also observed in the matured tree orchards treated with annual topical application of mulch with and without chicken manure when compared to the trees treated with growers' standard fertilizers. However, there was no significant difference between matured trees under topical application of mulch with or without chicken manure and young trees under pre-plant compost incorporation. This result suggested that the observed increase in TCSA either in matured trees or on young trees can be correlated to the observed numerical increase in the yield and productivity of the trees treated with compost and trees treated with or without chicken manure compared to the control treatment. Mature trees receiving mulch and/or mulch with chicken manure or young trees receiving compost produced similar yields and had a similar nutrient status while reducing or eliminating synthetic fertilizer applications. There have not been differences in other physiological parameters such as gas exchange. No other diseases and pests were observed in the experimental orchards.
Soil amendment did not change soil pH, but increased soil electrical conductivities in the mulch trials only. Similar amendment impacts were observed for soil NH4+ concentrations, enzyme activities, and active carbon at depths of 0-15 and 15-30 cm. Higher organic nitrogen mineralization potentials were found in orchard #2 when the soils were amended with mulch. However, no impacts on microbial respiration were observed. The results indicated that 1) soil amendments can improve soil nutrient availability and organic carbon content, which however depends on the sources of the amendments, 2) such improvement can reach soils at 30 cm, and 3) increased amendment rates may not produce proportional responses. A saturation effect may exist.
Educational & Outreach Activities
Participation Summary:
- Published a journal article.
- Lawrence, B., and Melgar, J. C. 2024. Effect of Municipal Mulch and Poultry Litter Amendments on Soil and Tree Parameters of a Mature Peach Orchard in a Humid Subtropical Climate. J. Soil Sci. Plant Nutri. Doi: 10.1007/s42729-024-01666-4.
- Conducted three on-farm spray trials during the dormant season.
- Published two Youtube videos.
- Soil Amendments(YouTube)
- Alternative ways to control diseases of peaches(YouTube)
- Presented two posters about this project at the Annual CAFLS Graduate Research Symposium, Baruch Institute of Coastal Ecology and Forest Science. About 140 Graduate students and professors attended this event.
- Ahmed, J., G. Schnabel, and Wang. Evaluation of organic pesticides against bacterial diseases of peach trees in dormant season. CAFLS Graduate Research Symposium, Georgetown, SC, October 2023.
- Idowu, A.P., Schnabel, G., Hopkins, J. and Melgar, J.C. 2023. Impact of soil amended with compost on orchard nutritional dynamics and horticultural performance, October 2023.
- Presented two talks at the SE Professional Fruit Workers Conference. About 80 agricultural professionals attended this meeting.
- Ahmed, J., A. Hill, E. Noh, G. Schnabel, and H. Wang. Evaluation of organic pesticides for managing bacterial spot of peach. SEPFWC meeting, Quincy, FL, November 2023.
- Idowu, A.P., Schnabel, G., Hopkins, J. and Melgar, J.C. 2023. Nutritional Status, Yield and Fruit Quality of a Peach Orchard in Response to Compost Application, November 2023.
- Presented a poster at the annual American Phytopathological Society (APS) Meeting. About 2,000 agricultural professionals attended this meeting.
- Ahmed, J., E. Noh, G. Schnabel, and H. Wang. 2023. Evaluation of organic pesticides against bacterial diseases of peach trees in dormant season. APS Annual Meeting, Denver, CO, August 2023.
- Presented a talk at the annual APS-Southern Division Meeting. About 100 agricultural professionals attended this meeting.
- Ahmed, J., G. Schnabel, and H. Wang. Evaluation of biopesticides for managing bacterial spot of peach. Southern Division APS Meeting, Columbia, SC, February 2023.
- Presented an e-poster for the young scholar internship program.
- Goergen, A., J. Ahmed, A.S. Hill, E. Noh, and Wang*. 2023. Development of sustainable strategies for managing bacterial diseases and improving tree health in the peach production system. Southern SARE Young Scholar Program, Virtual, September 2023.
- Presented a poster at the CU-CAT Ag Tech Spotlight Event.
- Ahmed, J., E. Noh, G. Schnabel, and H. Wang. Evaluation of organic pesticides against bacterial diseases of peach trees in dormant season. CU-CAT Ag Tech Spotlight Event, Clemson, SC, September 2023.
- Presented a talk at the CREF Research Session of the USCC Compost Conference 2024, in Florida. About 1600 professionals, including agricultural researchers, engineers, microbiologists, environmentalists, policymakers, and industries, including attended this conference.
- Idowu, A.P., Schnabel, G., Hopkins, J. and Melgar, J.C. 2023. Impact of soil amended with compost on orchard nutritional dynamics and horticultural performance, February 2024.
- Presented a talk about this project at the Peach Production Meeting in Walhalla, SC. About 15 farmers and agricultural professionals attended this meeting.
- Melgar, J.C. Peach Nutrient and Soil Management Trial Updates. Upstate Fruit Meeting, Clemson Extension, Walhalla, SC. March, 11, 2024.
- Presented a talk about this project at the Clemson Plant Pathologist Meeting. About 15 students and 5 faculty members attended this meeting
- Ahmed, J. Development of novel spray programs to improve management of bacterial diseases in peach trees. Clemson Plant Pathologist Meeting, March 2024.
- Presented at the EREC Fall Field day. About 30 Agricultural professionals attended the Field day.
- Wang, H. Management of peach bacterial diseases. EREC Fall Field Day – Row Crops and Fruits/Vegetables, September 2023.
- Presented about peach production at the SCNBFP annual workshop. About 40 farmers attended this workshop.
- Maintained a Clemson blog https://blogs.clemson.edu/pbds/ for this project.
- Trained three graduate students under this project. Trained three undergraduate interns.
Learning Outcomes
New biopesticide spray programs and soil practices