Towards sustainable disease management in northeastern apples using risk forecasts and cultural controls
An end-of-project grower survey was conducted in 2014 in New England to follow-up on the 2012 survey and further document grower experience with and adoption of the project’s apple scab management practices. It served to evaluate impacts of the study: changes in knowledge, actions, and conditions. Project scientists assisted growers in MA, NH, ME, VT, and CT with potential ascospore dose (PAD) assessments during Fall 2013 and with sanitation methods (urea applications and leaf-chopping) between leaf fall 2013 and the green tip bud stage in Spring 2014 at university orchards in MA, NH, and ME and at a total of 22 commercial sites in the region.
There were 17 “Test” plots of apple trees in 16 orchards which had low enough scab levels to “pass” the PAD assessment in the fall and to qualify for delaying the 1st scab spray the following spring until the pink bud stage. At 14 of these “Test” sites, the delay was performed successfully with an average delay in spraying (as compared to the non-delayed “Control” plots) of 9.4 days. While the other 3 “Test” sites did not delay the 1st spray of the spring scab season, they did reduce the number of sprays over the whole scab season as compared to their respective “Control” plots. Each spray event was converted into a dosage equivalent (DE). One DE = the maximum recommended field rate (MRFR) of a given pesticide. Over primary scab season (approx. 4/13-6/20 depending on location), there was as average reduction in DE of fungicide applications of 1.63 in the “Test” plots as compared to the “Control” plots. This is equivalent to a savings of 1.6 full-rate fungicide sprays for each site. This reduction in fungicide did not result in more scab in the leaves (end of June evaluations) or in the fruit (Sept. evaluations).
In the 5 orchard plots that had too much scab to pass the Fall PAD, the sanitation methods were performed in “Test” plots without the delays in the spring fungicide spray programs. Our intent was to help the growers reduce scab to levels that were not economically injurious and to prove to them the value of sanitation. We succeeded on both counts. In contrast to the unusually dry periods in 2013 and 2012 from green tip apple bud stage through pink, there were 2-4 infection periods during this interval in 2014. This gave us a good challenge. In the 17 “Test” blocks that were to be delayed, the protocol specified delaying until Pink or until 2 infection periods had passed. 14 growers complied perfectly and the other 3 complied with modifications. Decision-support for tracking infection risk and making pesticide recommendations was provided by project scientists and weather-based support tools (NEWA, Skybit, or AgRadar). Project concepts, methods, and results were presented and discussed in grower workshops, meetings, and publications.
Fifty apple growers will document adoption of scab management alternatives on a total of 500 acres, reducing their fungicide use and maintaining or reducing scab incidence in those blocks. Our calculations indicate that this should save a total of from $50,000 to $75,000 in production costs per year.
Our objective has been to work with New England apple growers to improve apple scab disease management in 3 specific areas: to improve methods of measuring scab inoculum in the field, to reduce scab inoculum by increasing and improving sanitation methods (urea sprays and leaf-chopping), and to make better use of decision support tools to track infection risks. These objectives have been carried out by a combination of university and commercial orchard research and demonstration trials, grower collaborations, educational events and publications, and grower surveys.
Under the guidance of UMass scientists, 15 sites in MA, CT, VT, and southwest NH were evaluated for fall leaf scab infestation in Oct. 2013. Nine of them had low enough levels of scab to pass the PAD test and thus qualify for the delayed 1st scab spray strategy for Spring 2014. The average number of days the blocks were delayed as compared to the “Control” plots was 9.4 days. At the time of that 1st scab spray, the average % maturity of the scab ascospores was 20%. Due to the delays, less fungicide was used in the “Test” plots: 5.5 dosage equivalents (DE) of fungicide as compared to 6.6 in the “Control” plots. “Test” plots also received urea applications and maximum leaf-chopping while “Control” plots received minimal leaf-chopping. Scab incidence was assessed in foliage in June 2014 and in fruit in Sept. and was found to be comparable to grower control blocks that received a standard fungicide program. In 7 of the 9 sites, injury was kept below the economic injury level. For 1 of the exceptions, the higher amount of fruit scab (12% incidence) was caused by the use of very low fungicide rates and by waiting too long to make the 1st application. The other high incidence of scab (8%) was probably caused by proximity to an abandoned orchard. At 5 additional sites, where blocks of apple trees failed the PAD in Fall 2012, the sanitation part of the study was performed. Test blocks received urea applications and maximum leaf-chopping. We defined maximum leaf-chopping as at least 2 passes with a flail or a rotary mower (and minimum as one pass). Many growers also added leaf-sweeping, leaf-raking and/or flexible arms that could get close to tree trunks to their maximum sanitation practices. Control blocks received no urea and less leaf-chopping. Fungicides were not delayed: rather a full protectant spray program was used from the green tip bud stage on. At 4 of the sites, there was very little scab in the leaves in June or in fruit in September in either of the plots. At the 5th site there was little scab in June, but a moderate amount appeared in the fruit in September. In both the Delayed and the Sanitation-only trials, plots ranged in size from 1 to 5 acres. Most plots were assessed for leaf scab in Fall 2014 (PADs were performed). Most growers indicated plans to continue with urea applications, leaf-chopping, and delays after the study is over. We believe this is a good indication of the positive impact of the project.
At 4 commercial sites in NH, 1 “Test” plot of apples was delayed until Pink or until 2 infection periods had passed. At the time of that 1st scab spray, the average % maturity of the scab ascospores was 21%. The fungicide dosage equivalents (DE) in the “Test” plots was 3.62 versus 4.12 in the “Control”. All “Test” plots received maximum leaf chopping. Some received urea applications as well. The “Control” plots had minimum leaf-chopping and no urea. The 3 other sites did not delay the 1st spray in the “Test” plots, but did reduce the overall number of sprays. The average DE in the “Test” plots was 4.6 versus 7.4 in the “Controls”. A savings of 2.8 fungicide full-rate applications was achieved. Scab levels were never higher in the “Test” plots (leaves or fruit) than they were in the “Controls” and were always well below 1 % incidence. All plots were assessed for leaf scab in Fall 2014, and all passed the PAD. All growers indicated plans to continue with urea applications, leaf-chopping, and delays where possible, even after the project is over.
At 4 commercial sites in ME, all “Test” plots of apples were delayed until Pink or until 2 or more infection periods had passed. The average number of days that the 1st spray was delayed was 9.8. At the time of that 1st scab spray, the average % maturity of the scab ascospores was 38%. The average fungicide dosage equivalents (DE) in the “Test” plots were 4.9 versus 6.12 in the “Control”. A savings of 1.2 fungicide full-rate applications was achieved. Scab levels were kept very low in all plots except for 1 “Control” plot, which had a fruit scab incidence of 5 %. All “Test” plots were assessed for leaf scab in Fall 2014, and all passed the PAD. All growers indicated plans to continue with urea applications, leaf-chopping, and delays where possible after the study is over.
Growers in this study have had the benefit of access to weather-based decision support tools (within NEWA or Skybit, or AgRadar) and training from project scientists on how to use these tools. Project scientists have purchased weather stations and annual contracts with NEWA for many of the growers that worked with UMass. They have also purchased Skybit data for farms that did not have on-site weather stations and have collaborated with Glen Koehler at UME to provide AgRadar for those sites. All of the growers routinely monitored scab forecasting from one of these sources and many had weather stations directly linked to NEWA. To make the information more accurate and site-specific, this project continues work in all 3 states to improve the scab ascospore maturation model. This includes new methods and equipment for spore-trapping and maturation assessment during primary scab season (designed by Bill MacHardy at UNH). We are working on methods to adjust the models to account for dry periods. We need to more accurately predict the beginning and end of scab season. UMass scientists have also been performing replicated spray trials to compare the advantages and disadvantages of using two data sources (RainWise weather stations and Skybit) with 4 analytical tools (NEWA, Skybit, AgRadar, and RIMPro) to time scab spray applications (see Publications).
Impacts and Contributions/Outcomes
Groups of apple growers were educated in scab management alternatives (SMA) at 1 grower seminar in late 2013 in NH and in 6 grower meetings in 2014 in NH and MA. The average number of attendees was 41. Topics included the delayed 1st spray strategy, sanitation strategies, reduced-risk fungicides, potential ascospore dose assessments (PAD), and use of decision support tools, such as NEWA and AgRadar. The concepts and strategies pertaining to scab management alternatives (SMA) were also presented at 5 grower twilight meetings in MA and RI, and at the eIPM Stakeholder’s Meeting (February in Grafton, MA) by UMass project scientists during March-June 2014. (approx. 30 attendees each). In all 3 states, project scientists worked with cooperating growers and their staff to train them in scab management alternatives. In 2014 we worked closely with 22 growers to implement and adopt advanced scab management alternatives via replicated trials. Several other growers participated in scab management activities that were not replicated. These activities were also discussed in April-June issues of Healthy Fruit (http://extension.umass.edu/fruitadvisor), J. Clements, editor, the Maine Tree Fruit Newsletter, and in the April-July issues of the New Hampshire Integrated Pest Management Newsletter (http://nhipm.wordpress.com). Frequent updates on apple scab ascospore maturity lab and field tests were sent out via these newsletters.
The New England Apple Scab Control Practices Survey
The survey that was conducted in May-July 2012 to learn about the state of apple scab management in commercial apple orchards within New England (published in Fall 2013 in Fruit Notes 78(4): 9-11 (http://extension.umass.edu/fruitadvisor) was followed-up with an end-of-project survey in April-July 2014. Both surveys were designed and analyzed by Renae Moran at UME. The results highlight impacts of the study. In summary, we obtained the following results from 77 responding growers:
- Sanitation, an approach to disease control implementing leaf-sweeping/raking/mowing/chopping and/or urea spraying, is practiced by 74% of surveyed growers in northern New England, an increase of 7% over the last two years. The proportion of acres in which sanitation was used increased by 23%.
- Scab indexing, a method to predict disease and to reduce the use of fungicide (includes the PAD or potential ascospore dose evaluations), is practiced by 24% of growers, an increase of 9% over the last two years.
- In 2014, 28% of the responding apple growers reduced fungicide use on all or part of their apple acreage by using sanitation, measuring the scab index or by growing resistant varieties.
Clements, J. and D. Cooley. A Comparison Of Two Sources Of Environmental Data And Three Model Outputs For Primary Apple Scab In 2012 At The UMass Cold Spring Orchard. Fruit Notes 78(2): 4-11. (https://cdn.sare.org/wp-content/uploads/20171204135414/954241delta-agenda2.pdf)
- Cooley, D., A. Tuttle, S. Villani, K. Cox, G. Koehler, T. Green, and P. Werts. Increasing fungicide use in New England apples. Fruit Notes 78 (Fall): 1-6. (http://umassfruitnotes.com/v78n4/a1.pdf)
- Cooley, D., A. Tuttle, J. Clements, S. Schloemann, and E. Garofalo. University of Massachusetts Fruit IPM Report 2014. Horticultural News 94 (Fall): 5-8. (https://cdn.sare.org/wp-content/uploads/20171204135414/954241delta-agenda2.pdf)
2014 or 2015. Moran, R. et al. The New England Apple Scab Control Practices Survey. Submitted to Fruit Notes.
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