Examining the Sustainability of Copper Use for Disease Management and Horticultural Benefit in Tart Cherry Systems

Examining the Sustainability of Copper Use for Disease Management and Horticultural Benefit in Tart Cherry Systems

Summary

Foliar copper fungicide spray programs were evaluated and determined to provide excellent control of cherry leaf spot, the most important fungal disease limiting tart cherry production. These results were incorporated into Extension outreach programming for tart cherry growers in Michigan. A survey of soils from six organic and four conventional tart cherry orchards in Michigan revealed that copper levels in soils rose in 7 of 9 orchards between 2006 and 2007. The possibility of utilizing alfalfa plants for copper hyperaccumulation from soil was studied. Results show that alfalfa plants could survive in soil containing up to 2,230 ppm copper.

Objectives/Performance Targets

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.

Accomplishments/Milestones

Objective 1: In 2006, copper was incorporated into fungicide spray programs in seven treatments in a trial conducted on Balaton and Montmorency tart cherry trees. In all cases, the use of copper was associated with excellent control of cherry leaf spot, a significant increase in control compared to non-treated trees. Reductions in both disease incidence and leaf defoliation were observed in the copper treatments. Phytotoxicity was not observed on the cherry trees following the copper applications.

Application of copper sprays for the control of cherry leaf spot on tart cherries in Traverse City, Michigan 2006.

Fungicide sprays were applied to a block of 12-yr-old Montmorency and 11-yr-old Balaton tart cherry trees at the Northwest Michigan Horticultural Research Station, near Traverse City, MI. This experiment was designed to test the efficacy of copper sprays as a possible substitute for conventional fungicides as part of a reduced-risk, IPM program. Single rows of Montmorency alternated with single rows of Balaton, and sprays were applied concentrate (6X) at 50 gallons of water per acre with a 3-point FMC airblast sprayer. Treatments were replicated 4-times on 3-tree plots of each variety with buffer trees between each plot. Spray dates and growth stages were: 9 May (bloom); 17 May (early shuck split); 26 May (first cover); 5 Jun (second cover); 15 Jun (third cover) and 29 Jun (fourth cover and final spray). Cherry leaf spot infection periods and their level of severity were identified on 2 May (low); 11 May (low); 12 May (moderate); 25 May (high); 28 May (low); 31 May (high); 6 Jun (moderate); 18 Jun (high); 26 Jun (moderate); 28 Jun (moderate); 1 Jul (moderate); 9 Jul (moderate); 17 Jul (moderate); 26 Jul (low); 1 Aug (high); 9 Aug (low); 14 Aug (low); 23 Aug (moderate); 24 Aug (low) and 26 Aug (moderate) (courtesy of www.enviroweather.com). Harvest dates for the Balatons and Montmorency were 28 Jul and 21 Jul respectively. The summer was dry with only 19 days of precipitation from 1 Jun to 22Aug that totaled 4.21 inches. As a result, cherry leaf spot developed late, and there was an unusually long interval of 54 days between the final spray and the evaluation on 15 Sep. Chemicals with strong protectant activity and/or visible residues gave the best control in this experiment.

The best control of both defoliation and leaf infection on Montmorency was achieved with two early sprays of Bravo Ultrex followed by a spray of Cuprofix at 3 lbs/A or Pristine at 10.5 oz and finishing with sprays of Elite plus Captan. Increasing the rate of Cuprofix from one lb to 3 lbs when applied during first, second, and third covers improved defoliation control on Montmorency but not on Balaton. Where Cuprofix was applied at second and third cover following Pristine, control of defoliation was not improved over other treatment schedules. The Balaton variety tended to have less defoliation than Montmorency which supports observations that while Balaton and Montmorency are similar in susceptiblity to cherry leaf spot, the Balaton variety does not defoliate as readily. On 15 Sep, all of the leaves on unsprayed Balaton and Montomorency were infected with leaf spot and more than 68% had fallen on Montmorency versus about 67% on Balaton. We observed no phytotoxicity.

Work left to do: These experiments need to be repeated to confirm the efficacy of copper in cherry leaf spot control. Also, the effect of coppers on other tart cherry diseases including brown rot and powdery mildew needs to be evaluated. More knowledge is also needed on the environmental parameters linking copper use to phytotoxicity.

Objective 2: Organic cherry orchards in Michigan which rely solely on copper fungicides for disease control have the potential to have elevated levels of copper in soils with repeated use. We found copper levels to rise dramatically in some organic orchards. For example, levels increased from 7.3 ppm to 37.8 ppm in one orchard and from 15.9 ppm to 46.6 ppm in another block. These initial observations and yearly analysis are driving our work to attempt to phytoremediate the copper from orchard soils, particularly because copper is a critical fungicide needed for disease control in organic systems.

Alfalfa plants have been studied in other systems in copper phytoremediation, and this plant species can survive and grow in soils containing up to 2,230 ppm copper. In our trials, we had 524 ppm copper in soil, and the plants appeared healthy.

Results from 90-day pilot experiments with alfalfa grown in copper-containing soils show that the plants can concentrate copper in roots. For example, after 30 days growth in soil containing 524 ppm copper, alfalfa roots contained 141 ppm copper versus 6.4 ppm at the beginning of the experiment. After 90 days, the concentration was 125 ppm. Likewise, with alfalfa planted in soil containing 2,230 ppm copper, after 30 days, the roots contained 530 ppm copper and 182 ppm after 90 days. We believe that the alfalfa plants would be beneficial in cherry orchards as a source to remove available copper from soils.

Objectives 3 and 4: A total of 21 Extensions presentations were given throughout Michigan by PI’s Sundin and Rothwell between 2005 and 2007 to educate growers about the use of copper to control cherry leaf spot in tart cherry orchards. In addition, one newsletter article was written in the MSU IPM Fruit CAT Alert, an online and written publication which, in an average week, reaches over 800 people.

Presentations:
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.

Newsletter Article:

Sundin, G.W, N. Rothwell. 2006. Cover spray options for cherry leaf spot control. MSU IPM Fruit CAT Alert, 5-16-06 issue.

Impacts and Contributions/Outcomes

The most important impact of this work is utilizing copper as an alternate fungicide for disease control in Michigan tart cherry orchards, particularly as copper is a broad-spectrum fungicide and has a critical alternative mode of action than many of our single-site fungicides on which we heavily rely. As other fungicide modes of action are lost due to both the evolution of fungicide resistance in important cherry pathogens and to regulatory restrictions, new fungicides are vital to maintain orchard productivity and grower profitability. However, the downside of copper use is the potential long-term impact on orchard systems as the heavy metal can build-up in soil. Our goal is to offset this negative impact by investigating plants that have the potential to accumulate copper from the soils. We hypothesize these plants will be effective at phytoremediating copper to reduce the potential negative impacts and to provide a closed-loop approach to sustainable orchard systems.

Collaborators: