- Fruits: general tree fruits
- Pest Management: general pest management
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.