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: Seventeen Bacillus strains from local fields were tested on nutrient agar plates against four strains of Xap, the pathogen causing bacterial spot in peach. Two commercial biopesticide products were included as control. There were two replications per treatment.
Four biopesticides were compared with copper (0.1 lb MCE/acre) and oxytetracycline (150 ppm) on peach trees in a greenhouse trial. Peach leaves were sprayed with biopesticide strains and air dry before spray-inoculation with a local Xap strain. The water spray followed by Xap inoculation and the biopesticide/chemical-only treatment were included as controls. Leaves were rated for disease incidence and severity at 4 weeks after inoculation. There were three replicates per treatment. Disease data were analyzed with a generalized linear mixed model in MiniTab.
In the 2022 growing season, 16 biopesticide spray treatments were evaluated in the peach field for managing bacterial leaf spot. Copper (0.1 lb MCE/acre) and untreated control were included as control. The spray treatments were applied every 7-14 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 2022 dormant season, we conducted two field trials to evaluate the effect of biopesticide treatments on Xap canker development. In the first trial, four treatments of commercial biopesticides and a copper treatment (2 lb MCE/acre) were sprayed for a total of four times during the leaf drop period. In the second trial, seven local Bacillus strains and a copper (2 lb MCE/acre) treatment were sprayed for a total of three times during the leaf drop period. In both trials, there were four replicates/trees per treatment; untreated control was included. Incidence and severity of spring canker were recorded from ten randomly selected twigs per tree in early spring. Thirty random buds from the 10 twigs per tree were pooled and processed with PMA-qPCR to quantify the viable Xap cells. Data were analyzed with a generalized linear mixed model in MiniTab.
Bacterial canker control: In the 2022 dormant season, we evaluated 10 biopesticide treatments for managing bacterial canker on peach twigs of potted trees using two different methods. In both methods, peach twigs with the same age were pruned and sprayed with each biopesticide strain, copper, or sterile tap water (control). Then, pruning cuts were: 1) spray-inoculated on the next day with a cocktail of Pss strains (108 cfu/ml) previously collected from bacterial canker in local peach orchards and wrapped with parafilm (method 1); or 2) exposed to natural infection through rain events and sprayed with the biopesticide/copper treatments two more times (method 2). Lesion length was measured after 3 months. There were four replications/twigs per treatment using each method. The experiment was conducted twice for both methods.
Objective 2: Assess sustainable soil management practices and their integration with spray programs on reducing bacterial diseases in research orchards.
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 (with or without chicken manure) to a mature orchard; 2) Addition of mulch to a young orchard that previously received composted mulch before planting (incorporated); and 3) Addition of compost to a young orchard that received compost from food waste before planting (incorporated). The mature orchard (#1) has natural presence of bacterial spot every year, but bacterial spot was spray-inoculated with a local Xap strain (106 cfu/ml) in the young orchards (2 and 3).
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 (gas exchange tree water status were measured monthly). 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. Fruit severity was evaluated with a visual scale (0-5). Xap canker was rated in spring.
Objective 1: Develop sustainable spray programs with biopesticides to reduce bacterial diseases.
Bacterial spot control: All Bacillus strains showed inhibition zones (2.5-3.75 mm) against the four Xap strains tested, indicating that they can directly antagonize Xap growth and have potential to improve bacterial spot control on peach trees.
In the greenhouse trial, none of the biopesticide and chemical treatments was able to reduce bacterial spot incidence and severity compared to the untreated control, suggesting that one spray of the biopesticides and chemicals is not enough to suppress the disease development from Xap inoculation in the greenhouse. Weekly spray of biopesticides will be tested in the future greenhouse trials.
In the field trial of the 2022 growing season, two biopesticide treatments significantly reduced the bacterial spot incidence and provided statistically similar efficacy as copper. However, copper caused significant phytotoxicity on peach leaves whereas the biopesticide treatments did not. These results suggest that these two biopesticides could have potential to serve as alternative options in a spray program to improve management of bacterial spot. They will be further tested in the 2023 field trial.
In the first dormant season trial, one commercial biopesticide product significantly reduced the spring canker incidence and severity compared to the untreated control. Copper was able to reduce the spring canker incidence but not the severity. In the second dormant season trial, one local biopesticide strain and the copper treatment significantly reduced the spring canker incidence and severity and there was no statistical difference between these two treatments. The PMA-qPCR samples are being processed in the lab now. These results indicate that the biopesticide and copper spray program in the dormant season could contribute to reduced spring canker, which is the major inoculum source for bacterial spot in the growing season. The dormant season trial will be repeated in 2023.
Bacterial canker control: With natural infection (method 2), the untreated control had the longest canker lesions; seven spray treatments (six biopesticides and one copper) significantly reduced the canker lesions. With artificial inoculation (method 1), there were no statistical differences among treatments, which could be possibly explained by the high disease pressure from high inoculum concentration. These results indicate that natural infection (method 2) is a better method in evaluating treatments for bacterial canker control and the dormant season sprays of biopesticides have significant effect in reducing bacterial canker. The trial will be repeated in 2023 with method 2.
Objective 2: Assess sustainable soil management practices and their integration with spray programs on reducing bacterial diseases in research orchards.
The addition of mulch to a mature orchard where natural infections of bacterial spot are found every year resulted in reduced incidence and severity of bacterial spot in those trees that received mulch (with or without chicken manure), compared to control trees that did not receive mulch (bare soil). Compost additions have not shown significant differences on bacterial spot as the pressure in those orchards was very low.
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. Soil amendments also increased tree trunk cross-sectional area (TCSA) compared to bare soil when incorporated at planting and added to young orchards. Nevertheless, no differences in TCSA have been observed when amendments were applied to a mature orchard. So far, there have not been differences in other physiological parameters such as gas exchange.
In regard to soil water holding capacity, soil moisture sensors indicated that amendments buffered the soil from drying out at 15 cm depth, although this did not appear to have influence on yield of mature trees, as they have access to moisture at lower soil depths. Soil cores also showed that soil amendment increased soil water content when soil was amended with mulch, which however was not observed when compost 1 and 2 were applied. The results suggested that organic inputs increase water availability for fruits, which however is not linear and may be greatly dependent on the quality and quantity of the amendments. No significant differences were observed in leaf gas exchange among different treatments.
Higher soil inorganic nitrogen was observed when soil amendments were applied, regardless of the quantity, however, the extent of which was less significant for compost treatments when compared to mulch, suggests increased soil fertility resulting from some soil amendments compared to others. Regardless of amendment types, the application increased potentially mineralizable nitrogen, suggesting higher organic nitrogen mineralization rates when amendments were added. Soil amendments also stimulated soil microbial activities, as demonstrated by increased soil respiration and enzyme activities. The decomposition of organic materials provided energy and nutrient sources to induce microbial activities.
In summary, the first-year data generally indicated that soil amendment improved soil functions associated with water retention, microbial activities, and nutrient cycling. However, the quality and quantity of the amendment may affect the outcomes.
Educational & Outreach Activities
Participation Summary:
- Surveyed underrepresented minority producers for needs assessment through Sierra Club, SCNBFP, SC WAgN, and our collaborator Julian Nixon. Surveys were also given out at the Appreciation Festival for Farmers and Farmworkers in Rembert, SC.
- Presented a poster about this project at the Southeast Regional Fruit and Vegetable Conference. Over 200 farmers and agricultural professionals attended this conference.
- Wang, H., G. Schnabel, J.C. Melgar, R. Ye, M. Vassalos, and B. Blaauw. 2023. Development of sustainable strategies for managing bacterial diseases and improving tree health in the peach production system. Southeast Regional Fruit and Vegetable Conference, Savannah, GA, January 2023.
- Presented a talk about this project at the Peach Production Meeting in Edgefield, SC. About 40 farmers and agricultural professionals attended this meeting.
- Schnabel, G. Peach Disease Management. Peach Production Meeting, Clemson Extension, Edgefield SC. February 2023.
- 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 2023.
- Presented a talk about this project at the Materials Innovation for Sustainable Agriculture (MISA) symposium. About 50 agricultural professionals attended this meeting.
- Wang, H. Management of bacterial spot in the southeastern peach production. 2022 MISA Symposium, Orlando, FL, October 2022.
- Presented an invited seminar about this project at the Presbyterian college. About 30 students and 10 faculty members attended this seminar.
- Wang, H. Towards a better understanding and improved management of plant bacterial diseases. Seminar, Presbyterian College, Clinton, SC, April 2022.
- Presented a round table on soil health of peach orchards that included a discussion on field studies part of this project at the Southeast Regional Fruit and Vegetable Conference. About 20 farmers and agricultural professionals attended the discussion.
- Presented about peach production at the SCNBFP annual workshop. About 40 farmers attended this workshop.
- Presented a talk at the SE Professional Fruit Workers Conference. About 70 agricultural professionals attended this meeting.
- Lykins, S., Lawrence, B.T., Melgar, J.C, and Schnabel, G. 2022. Bronzing and bacterial spot in peach trees under municipal mulch and chicken litter soil amendments. Southeastern Professional Fruit Workers Conference, Lake Alfred, FL, November 2022.
- Established a Clemson blog https://blogs.clemson.edu/pbds/ for this project. The Blog will contain information about the PI’s, the project objectives, and the progress of the project.
- Gave four tours of the experimental orchards to six stakeholders (from compost/mulch and fertilizer companies); the different soil management treatments, and the impact on reducing synthetic fertilization and on tree health were discussed with them.
- Recruited and trained three graduate students under this project. Trained five undergraduate interns.
- The PIs and students on the project presented annual progress to the farmer cooperators, collaborators, and advisory board at the annual project team meeting in January, 2023. The meeting notes were sent to the whole project team afterwards.
- A news article was published about this project.
- Attaway, D. 2022. Grant helps Clemson researchers fight peach bacterial diseases, support underserved producers. https://news.clemson.edu/grant-helps-clemson-researchers-fight-peach-bacterial-diseases-support-underserved-producers/?utm_source=rss&utm_medium=rss&utm_campaign=grant-helps-clemson-researchers-fight-peach-bacterial-diseases-support-underserved-producers
Learning Outcomes
N/A
Information Products
- Grant helps Clemson researchers fight peach bacterial diseases, support underserved producers (Article/Newsletter/Blog)
- Bacterial diseases need our attention (Website)