Foliar copper fungicide spray programs were evaluated for multiple years and were provided excellent control of cherry leaf spot (CLS), the most important fungal disease limiting tart cherry production. These results were incorporated into Michigan State University Extension (MSU-E) programming for Michigan tart cherry growers. By incorporating two cover sprays of copper for CLS control, growers saved approximately $70/acre compared to ‘standard’ fungicide programs that did not utilize copper. In addition to cost savings, the potential for Blumeriella japii, the pathogen that causes CLS, to develop resistance to copper is low. Because of these advantages, grower adoption of copper use as a foliar fungicide has increased approximately 11% between 2007 and 2009. In order for copper to remain a viable and sustainable option for tart cherry growers, we investigated phytoremediating organisms that would minimize copper build up in the soils. Greenhouse experiments revealed that alfalfa plants were not efficient in hyperaccumulating copper from soils. The potential for using copper-accumulating soil bacteria in remediation was examined, and copper-resistant bacteria were isolated from orchard soils that accumulated copper in laboratory growth media. Two promising copper-resistant bacterial strains were shown to survive over a 45-day period in orchard soils. These bacteria need to be further field tested for use as copper accumulators in orchard soils containing elevated copper levels. Over the course of the project period, the co-PI’s delivered 48 extension talks to growers and published five articles on copper use for CLS control and on copper bioremediation from soils.
Michigan is the leading producer of tart cherries (Prunus cerasus L.) in the nation with 10,926 bearing hectares (27,000 acres), and the North Central region (primarily MI and WI) produces 84% of the nation’s tart cherries (NASS 2003). Traditionally, tart cherries have been sold frozen, canned, or dried for use in the baking industry. However, in recent years, studies have shown that tart cherries are a potent source of antioxidants and have many health benefits. Additionally, the introduction of the new cultivar ‘Balaton’ has opened new markets, both in processing and fresh sales. In addition to direct sales and the farm gate value, the cherry industries in northwestern Michigan and the Door Peninsula of Wisconsin are vital to the thriving tourism industries of those regions. For example, the National Cherry Festival in Traverse City, MI is conservatively estimated to contribute $15 to 20 million annually to the local economy (Anonymous 2003).
Major constraints to economically viable tart cherry production include fungal diseases, of which cherry leaf spot (CLS) caused by the pathogen Blumeriella jaapii (Rehm) is the most important, and soft fruit, a more recent problem that can significantly reduce yield during harvest. Because most of the Michigan tart cherry acreage consists of the CLS-susceptible cultivar ‘Montmorency’ and the new ‘Balaton’ cultivar is also susceptible to CLS, fungicide inputs of up to eight seasonal applications are required for adequate disease control. Currently, the development of fungicide resistance in the CLS pathogen to the sterol inhibitor (SI) class of fungicides has seriously impacted effective CLS control in Michigan. In some orchards, outright control failures of SI’s have resulted in severe CLS infections leading to the death of significant numbers of trees due to winter kill.
Due to the paucity of available fungicide chemistries that incorporate different modes of action, we have been reevaluating the use of copper compounds as an alternative fungicide for control of CLS and SI-resistant B. jaapii in Michigan orchards. Copper was widely used for tart cherry disease control in the 1930s and 1940s until its gradual replacement by modern synthetic fungicides. Successful efficacy of copper compounds aids both conventional growers, as copper extends the life of traditional fungicides, and organic growers because copper is the only viable option for disease control in tart cherry. Copper is also about one-third the cost of traditional fungicides, an attribute that lends appreciably to the economic stability of Michigan orchards, particularly smaller orchard operations.
One potential detriment to a re-introduction of copper into widespread use in tart cherry orchards is the possibility of phytotoxicity effects due to copper build-up in soils. Copper is naturally present in all soils at normal ranges of 8-150 mg kg-1, and typically accumulates in the upper 15 cm of soil, where it is bound to organic matter and clay particles (Baker 1990). An unfortunate consequence of sustained copper usage for disease control is an increase in soil copper levels, which eventually leads to tree decline and long-term reductions in orchard health. For example, the prolonged use of copper in citrus groves in California and Florida has resulted in increased levels of copper in soils which has a direct negative effect on tree health; indirect effects of copper use also impacts beneficial organisms such as mycorrhizal fungi as high levels are toxic to these organisms. Copper concentrations as high as 1,500 mg kg-1 have been reported in agricultural soils where repeated copper applications have occurred.
Microbial remediation is a potentially viable solution to copper build-up in soils and is a process that uses specific copper-accumulating bacteria that remove potentially toxic metal ions from the soil. We hypothesize that these bacteria will accumulate copper, thereby limiting copper availability in soil and therefore the potential toxic effect of the elevated copper levels to cherry trees.
The following objectives were addressed in this proposal:
1. To incorporate foliar copper sprays into tart cherry management programs on commercial and organic farms in Michigan and to evaluate its efficacy on key diseases including CLS and to investigate copper’s potential to reduce soft fruit at harvest.
2. To assess the potential of copper-hyperaccumulating plants in removing copper from agricultural soils in greenhouse experiments and at on-farm sites.
3. To educate tart cherry growers about the utility of copper in their management programs and about phytoremediation.
4. To increase the adoption of these practices in the long-term in an effort to promote agricultural sustainability.
Evaluation of copper in the control of fungal diseases of tart cherry. We evaluated copper fungicides for disease control in tart cherry orchards both on-farm and at the Northwest Michigan Horticultural Research Station. In short, replicated field plots were set up and various spray treatments of copper fungicides were used and compared ot conventional fungicide programs. Disease ratings were conducted to determine the percentage of infection due to CLS, brown rot, and powdery mildew.
Copper content in soils from tart cherry orchards. We examined the copper content in soils in the spring of 2006 to establish baseline copper levels prior to remediation experiments. The level of available copper ions in soils at the orchard sites prior to and during the experiments was determined by mass spectroscopy of bulked soil samples taken along transects in each block. Sampling locations were mapped using a portable global positioning system (GPS) device for return sampling.
Bioremediation of copper from contaminated soils. Our initial experiments with copper accumulation from soils utilized alfalfa plants. Alfalfa plants were tested under greenhouse and field conditions for their ability to accumulate copper from soils and to partition the copper into their above-ground (leaf and stem) tissue. Plants were grown in soils containing approximately 60-120 ppm copper in the greenhouse experiments and in natural orchard soils in field experiments. In both sets of experiments, plants, roots, and soil were sampled 30-90 days after planting. In two separate greenhouse experiments, levels of copper in alfalfa roots and shoots increased only slightly after 90 days growth in soil amended with copper (see data in 2008 report). In the field experiment, alfalfa plants were planted into pots placed under the drip-line of tart cherry trees that received two applications of copper fungicides. The alfalfa plants grew considerably well under the shady orchard conditions, but there was no evidence of copper accumulation into the roots or shoots of the plants.
These results, combined with the loss of a key collaborator on the project who left MSU, led us to study the use of copper-resistant soil bacteria to bind copper ions in soil. We initiated a study to isolate and identify copper-resistant bacteria from soil samples collected from six organic tart cherry orchards in northwest Michigan. Many copper-resistant bacteria turn blue when grown on copper-amended growth medium in petri dishes in the lab. Copper-amended medium is blue due to the color of copper solutions. When copper-resistant bacteria absorb copper from the medium, the bacteria become progressively more blue as the medium loses its blue color. We hypothesized that copper-resistant bacteria could be used to bind copper present at elevated levels in contaminated soils. While the copper would not be removed from soils using this strategy, the copper will be bound to the bacteria and thus unavailable for uptake by cherry roots. This then acts as to protect the cherry roots from copper exposure.
A total of 120 bacterial isolates were recovered from soil, and they were tested for their ability to grow on media with high levels of copper: 250, 500, 750, and 1000 ppm. Ten isolates grew most vigorously on media with 1000 ppm copper; these bacteria produced blue or green colonies on the high copper media, suggesting that these species were taking up copper from the media. Two of these bacteria were selected for field studies in soil. To facilitate this work, a spontaneous antibiotic (rifampicin) resistant strain was developed from each of the selected isolates in order for bacterial populations to be tracked in soil. These bacteria were then inoculated into field soil at two locations and tracked using plating on rifampicin-amended media over a 45-day period to determine if the bacteria could successfully colonize and persist in the soil.
Objective 1. The experiments utilizing foliar copper sprays for fungal disease control of tart cherry were completed in 2008. These experiments were highly successful and established copper as an excellent fungicide for cherry leaf spot control. Consistent, positive results were observed for copper efficacy against CLS in the experiments conducted in 2006, 2007, and 2008.
We also evaluated the effects of copper utilization on soft fruit in 2006 and 2008. Montmorency tart cherries often lack firmness at harvest, which can result in losses to growers and processors conservatively estimated at $6.3M per year (J. Nugent, personal communication). To alleviate the frequency of soft fruit, we have examined the use of copper to reduce the incidence of this problem. In 2006 and 2008, we found that one application of copper resulted in orchards with slightly less incidence of soft fruit (3.72%) than orchards that received no copper (5.5%). No copper was applied in these orchards in 2007 due to high temperatures. At this time, we cannot conclude if minimal applications of copper will reduce the amount of soft fruit; however, increasing the number of sprays per season may result in firmer fruit.
Objective 2. A study leading to the use of bacteria as copper accumulators from contaminated soil was initiated in 2008 and continued into 2009 and a field study was conducted. From an initial 120 bacterial isolates, 10 highly copper-resistant isolates were recovered and tested for long-term persistence in soil. We use marked strains with spontaneous rifampicin resistance so that we could track each isolate. Suspensions of the antibiotic resistant isolates were inoculated into sterile soil in covered plastic containers in the lab. Soil samples were taken immediately following inoculation and after 2, 7, and 14 days. Dilution platings were made on rifampicin-containing media to measure the bacteria concentrations in the soil over time. Further sampling was done after 3 or 4 weeks for the most promising isolates. From these experiments, two isolates (GT8.1 and GT10.1) were selected to be tested in the field this summer. These bacteria were successfully recovered from field soil over a 45-day period. Thus, these bacteria represent excellent candidates for field remediation of copper from contaminated orchard sites.
We also monitored soil copper levels in orchards that we had sampled previously in 2006 and 2007. The results illustrated that copper levels had actually decreased in two of the orchards (A and B) even though copper fungicides were applied in these orchards in 2008. Since copper has been used for a period of years in these orchards now, we wonder if the bacterial flora in the soils of these orchards has been modified to select for increased copper resistance, and if these resistant native bacteria are already functioning to reduce the bioavailable copper load in these soils. This is an exciting prospect for the long-term sustainability of copper use for disease management programs in tart cherry.
Objectives 3 and 4. A total of 48 Extensions presentations were given throughout Michigan by PI’s Sundin and Rothwell during the 2006 to 2009 project period to educate growers about the use of copper to control cherry leaf spot in tart cherry orchards. In addition, five newsletter articles were written in the MSU IPM Fruit CAT Alert, an online and written publication which, in an average week, reaches over 800 people. The presentation and article information is compiled in the 2007, 2008, and 2009 reports and is also presented in the Publications/Outreach section.
This project was highly successful in establishing the efficacy of copper for fungal disease management in tart cherry. As the cherry industry struggles with the loss of fungicides to resistance issues, copper represents a low-cost alternative, that is as or more effective than existing fungicides, and also is not prone to resistance development. We also addressed negative issues related to copper use, namely the potential for phytotoxicity and the potential for copper accumulation in soils. While the use of plants for phytoremediation was one possibility, the deployment of plants in orchards for this purpose would have been technologically difficult for growers. We believe that the use of copper-accumulating bacteria has high potential for use and that these organisms could be deployed by spraying. Our work has identified excellent candidate organisms for this purpose.
Copper use in northwest Michigan for cherry leaf spot (CLS) control has increased by 15% in a three-year period based on increased copper sales in the region (M. Evans, personal communication). In 2009, we documented more calls, orchard visits, and questions at IPM Updates regarding copper use than in all years of the project (>45). We hypothesize that the interest was driven by cool growing conditions as well as multiple years of communication by MSU Extension personnel regarding the successful incorporation of copper into fungicide spray programs. Additionally, the information has spread to Wisconsin and Ontario tart cherry growers, who are now using copper in their orchards. The increase in copper use may also be influenced by our studies that show minimal phytotoxicity, even under 90 degree F conditions with no lime as a saftener. Additionally newer formulations of copper have built-in saftening components, and growers have a higher comfort level with these products.
Integrating copper into a standard fungicide program has the potential to be beneficial for tart cherry growers in three ways: 1) economically advantageous, 2) biologically sustainable, and 3) efficacious against the most devastating fungal disease, cherry leaf spot. As evident in the economic analysis (see below), copper provides an inexpensive option for CLS control; at this time, costs for copper applications are approximately $7/acre compared to traditional fungicides at a cost of $35-$44/acre. These substantial savings greatly impact grower returns, particularly for smaller farms where profit margins are much narrower. Copper also has been shown to have lower risk of developing fungicide resistance compared with the other fungicides. For example, both stobulurins and sterol inhibitors are both at high risk of fungicide resistance development and are estimated to develop resistance within 25-40 applications. Because copper is not prone to resistance, growers can maximize its use and its potential longevity in the field. Lastly, we have shown copper to be highly efficacious against CLS at a 1.2lb actual Cu rate. In fact, copper in high pressure blocks, such as organic orchards that have no other effective materials, keep leaves for one to two weeks longer than orchards that do not apply copper. However, to reap the full advantages of copper, we need further testing and refinement of remediating bacteria in tart cherry systems.
Despite the change of direction of the phytoremediation portion of the project, we feel the copper-accumulating bacteria show tremendous potential to bind copper in the soil. Our 2009 preliminary data in the field show that bacteria survive and reproduce in soil amended with copper. We hope to continue these field trials and expand this concept in future studies. The use of copper-resistant bacteria for phytoremediation, although at its initial stages of field testing, offers promise for increasing the utility of a critical fungicide and for orchard sustainability through maintaining soil health.
Because copper is an inexpensive choice for CLS control, integrating copper into a tart cherry fungicide program is economically beneficial. With two copper cover sprays in a standard program, growers spend $162/acre compared to $232/acre, a savings of $70 per acre per season.
Because copper has economic advantages over standard fungicides, we thought growers would readily adopt copper cover sprays into their cherry leaf spot (CLS) control program. However, many growers had past experiences or heard anecdotal reports of incidences with phytotoxcity caused by copper applications. Therefore, we conducted further studies that measured environmental conditions that could potentially amplify copper phytotoxicity in order to improve grower adoption. For two years, we measured temperature and rainfall and the incidence of copper phytotoxicity; our results showed no measurable phytotoxicity at temperatures as high as 32ºC (90ºF). These results coupled with our data demonstrating effective CLS control with copper has increased the amount of growers using copper in their fungicide programs. Additionally, growers have not only used copper more readily for CLS control, but they also have increased the number of sprays per season (from one to two applications), particularly in cool seasons such as 2009. This season, at six on-farm demonstration sites, two copper applications were incorporated into tart cherry fungicide programs. Lastly, copper sales to cherry growers have increased 11% in the past two years.
Educational & Outreach Activities
1. Resistance to sterol-inhibitor fungicides in the cherry leaf spot pathogen: status in Michigan and alternative control strategies. Northwest Orchard and Vineyard show, Traverse City, MI, 1-18-05.
2. Resistance to sterol-inhibitor fungicides in the cherry leaf spot pathogen: status in Michigan and alternative control strategies. Southwest Hort Days, Benton Harbor, MI, 2-3-05.
3. Cherry leaf spot. IPM Fruit School, Hickory Corners, MI, 2-14-05.
4. Stone fruit disease management. Spring meeting, Hart, MI, 2-24-05.
5. Tree fruit disease update and stone fruit disease management. Spring meeting, Flint, MI, 2-25-05.
6. Tree fruit fungicides. Understanding pesticides workshop, Fennville, MI, 3-18-05.
7. Cherry leaf spot control. Wilbur-Ellis grower meeting, Hart, MI, 3-16-05.
8. Cherry leaf spot trials. NWMHRS open house, 8-23-05.
9. Resistance to SI fungicides in the cherry leaf spot pathogen. Great Lakes Fruit Workers meeting, E. Lansing, MI, 11-2-05.
10. Tree fruit disease update. Southwest Hort Days, Benton Harbor, MI, 2-9-06.
11. Disease management update. Spring meeting, Hart, MI, 2-27-06.
12. Apple and stone fruit disease control update. Spring meeting, Flint, MI, 3-10-06.
13. Mode of action and performance of fungicides for brown rot and leaf spot control. IPM Cherry advanced training, 3-14-06.
14. Fungicide and antibiotic resistance management. IPM Cherry advanced training, 3-14-06.
15. Cherry IPM update. Leelanau grower meeting, 6-07-06.
16. Cherry IPM update. Old Mission grower meeting, 6-07-06.
17. Cherry leaf spot trials. NWMHRS open house, 8-24-06.
18. Cherry leaf spot management in 2007. Northwest Orchard and Vineyard show, Traverse City, MI, 1-16-07.
19. Modes of action of fungicides and copper. MSU Tree Fruit IPM school, Hickory Corners, MI, 1-29-07.
20. Tree fruit disease update. Southwest Hort Days, Benton Harbor, MI, 2-06-07.
21. Tree fruit disease update. Benzie-Manistee Hort Show, Crystal Mountain, MI, 3-14-07.
22. Disease management update. Spring meeting, Hart, MI, 3-16-07.
23. Disease control update for 2007. Spring Tree Fruit meeting, Grand Rapids, MI, 4-19-07.
24. Disease control update for 2007. Spring Tree Fruit meeting, Belding, MI, 4-26-07.
25. RAMP report, plant pathology update. Great Lakes Fruit and Vegetable EXPO, Grand Rapids, MI, 12-05-07.
26. Fungicide Resistance Issues in Important Cherry Diseases, Northwest Orchard and Vineyard Show, Traverse City, MI, 1-16-08.
27. Cherry leaf spot: life after DMI’s. Northwest Michigan Orchard and Vineyard show, Traverse City, MI, 1-17-08.
28. RAMP Management Team Meeting, Northwest Michigan Horticultural Research Station, Traverse City, MI, 1-18-08.
29. Aspects and management of bactericide and fungicide resistance in tree fruit pathogens. Michigan State University Department of Horticulture, East Lansing, MI, 2-28-08.
30. Tree fruit disease update for 2008. West Central Spring Tree Fruit meeting, Hart, MI, 3-06-08.
31. Copper Use in Tart Cherry Systems. Benzie-Manistee Horticultural Society Annual Meeting, Benzonia, MI, 3-11-08.
32. Fungicide Spray Programs for Tart Cherry Growers, Spring IPM Kick-off, NW Michigan, Hort. Research Station, Traverse City, MI, 4-9-08.
33. Disease control update for 2008. Spring Tree Fruit meeting, Grand Rapids, MI, 4-17-08.
34. Cherry IPM update. Leelanau County grower meeting, 5-14-08.
35. Cherry IPM update. Old Mission Peninsula grower meeting, 5-14-08.
36. Cherry IPM update. Benzie-Manistee Counties grower meeting, 5-27-08.
37. Tart cherry disease trial results, 2008. Northwest Michigan Horticultural Research Station Open House, 8-21-08.
38. Continuing to Investigate Copper Use for Cherry Leaf Spot Control,
NWMHRS Annual Open House, 8-21-08.
39. Disease control highlights, 2008. Tree Fruit Organic Field Day, Flint, MI, 11-11-08.
40. Stone fruit disease control. Great Lakes Fruit and Vegetable EXPO, Grand Rapids, MI, 12-08-08.
41. Cherry leaf spot: 2008 trial results. Northwest Michigan Orchard and Vineyard show, Traverse City, MI, 1-21-09.
42. Tree fruit disease update for 2009. Southwest Michigan Hort Days, Benton Harbor, MI, 2-04-09.
43. Disease control update, 2009. West Central Spring Tree Fruit meeting, Hart, MI, 3-16-09.
44. Cherry Leaf Spot: 2008 Field Trial Results, Northwest Michigan Orchard and Vineyard Show, Traverse City, MI, 1-21-09.
45. Cherry IPM update. Leelanau County grower meeting, 5-20-09.
46. Cherry IPM update. Old Mission Peninsula grower meeting, 5-20-09.
47. Cherry IPM update. Antrim County grower meeting, 6-9-09.
48. Cherry IPM update. Benzie-Manistee Counties grower meeting, 6-9-09.
1. Sundin, G.W, N. Rothwell. 2006. Cover spray options for cherry leaf spot control. MSU IPM Fruit CAT Alert, 5-16-06 issue.
2. Sundin, G.W., and N.L. Rothwell. 2007. Fungicide cover spray considerations for cherry leaf spot control. MSU IPM Fruit CAT Alert, 5-15-07 issue.
3. Rothwell, N.L., and G.W. Sundin. 2007. Postharvest sprays for cherry leaf spot. MSU IPM Fruit CAT Alert, 7-24-07 issue.
4. Sundin, G.W., and N.L. Rothwell. 2008. Managing cherry leaf spot in poor spraying weather. MSU IPM CAT Alert 6-24-08 issue.
5. Sundin, G.W., N. Rothwell, and E. Lizotte. 2009. Fungicide cover spray considerations for cherry leaf spot control. MSU IPM Fruit CAT Alert, 6-09-09 issue.
Areas needing additional study
The one area of work needing additional study in this project is an evaluation of the copper-resistant bacteria in the accumulation of copper from soil and the potential deployment of these organisms in orchards. We are hoping to gain funding to pursue these studies during the 2010 season. Additionally, we need to further refine the use of copper accumulating bacteria in order to make recommendations to growers on proper and sustainable copper use in orchards and bacterial deployment.