Towards sustainable disease management in northeastern apples using risk forecasts and cultural controls

Towards sustainable disease management in northeastern apples using risk forecasts and cultural controls

Summary

A grower survey distributed in Spring 2012 defined current apple scab management practices and charted a course of collaboration for project scientists and growers. Collaborators began research and demonstration trials at 3 university research farms and 6 commercial orchards. Methods of measuring scab inoculum, reducing inoculum load, and delaying fungicide applications in Spring 2012 until the pink bud stage were tested and employed successfully in all sites. The season was early and unusually dry at that time. Fungicide applications were also delayed to bloom in 2 trials and to petal fall in another. Decision support for tracking infection risk and making pesticide recommendations was provided by project scientists and weather-based support tools like Orchard Radar and NEWA. Project concepts, methods, and results were presented and discussed at grower workshops and meetings. Several more orchards entered the project in Fall 2012.

Objectives/Performance Targets

Our objective for the 1st several months of the study 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 using 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 collaboration and education events, and a start-of-project grower survey.

Performance target: 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.

Accomplishments/Milestones

Project scientists assisted grower collaborators with potential ascospore dose (PAD) assessments during Fall 2011 in preparation for the beginning of the study. Between leaf fall in Nov. 2011 and the green tip bud stage in Spring 2012, urea application and leaf-chopping sanitation was discussed and documented for the commercial and university orchard sites.

Under the guidance of UMASS scientists, the 1st scab spray was delayed in apple blocks until the pink bud stage in Spring 2012 at 6 commercial sites in MA, CT, VT, and southwest NH. Scab incidence was assessed in foliage in June and in fruit in Sept. and was found to be comparable to grower control blocks that received a standard fungicide program. In all cases, injury was kept well below the economic level. At 2 of the sites (Walpole, NH and Saxton’s River, VT) there were infection periods before the pink bud stage.

At the UMASS research farm, test plot fungicide applications were delayed successfully until the pink bud stage, but were unsuccessful when pushed further to the bloom stage. A significant infection period occurred between the 2 dates and too much unprotected green tissue was infected.

At the UNH research farm, test plot fungicide applications were successfully delayed to the petal fall bud stage after 3 infection periods had occurred in 1 trial and until the pink bud stage in another trial. As in MA and ME, scab incidence was assessed in foliage in June and in fruit in September.

At the UME research farm, test plot fungicide applications were successfully delayed to the pink and to the bloom bud stages. Powdery mildew was also assessed and was not found to be higher in plots that had delayed fungicide programs.

In most of the research sites in 2012, there were no infection periods before the pink bud stage. For this reason, the UNH trial pushed one of the treatments to petal fall (by which time 3 infection periods had occurred, as noted above). Because of very early spring in 2012 with unusually dry weather between the green tip and pink bud stages the scab management alternatives did not get a rigorous challenge. Traditionally, apple growers in New England start spraying for scab at green tip. If they were not calculating their infection periods carefully in 2012, they might have applied 2 or more unnecessary applications before the pink bud stage. Growers in this study, however, had the benefit of access to weather-based decision support tools (within NEWA and/or Orchard Radar) and training from project scientists on how to use these tools. This part of the study benefitted all. As we were adjusting to the erratic and unusual weather patterns we discerned that the scab ascospore maturation model was not accurately predicting the beginning or end of primary scab season. This finding has spurred research within the project to test and improve the model.

In Fall, 2012, all the grower sites were re-visited and another round of PAD assessments were performed, many with the growers, to prepare for the 2013 season. Three additional orchards were added to the study in MA. Sanitation strategies were planned with all growers. Plans for delayed 1st scab spray and/or leaf sanitation experiments are underway for 2013 at 2 university research facilities and at 10 commercial sites directed by UMASS (MA, CT, VT, and 1 in NH), 3 commercial sites directed by UME and 3 by UNH.

Impacts and Contributions/Outcomes

The major impacts of the 1st several months of the study have been in increased knowledge and changes in actions of the apple growers as well as the project scientists. Grower education events have led to increased collaboration and implementation of scab management alternatives (SMA).

Two workshops/advisory meetings, one in MA (Oct.) (18 attendees) and one in ME (Aug.) (70 attendees), were held in 2012 to train groups of apple growers in scab management alternatives (SMA). The trainings included developing reduced fungicide and sanitation strategies, demonstrations of potential ascospore dose assessments (PAD), and use of decision support tools, such as NEWA Orchard Radar. William MacHardy, Daniel Cooley, Glen Koehler, and Renae Moran were featured speakers/leaders in ME. Daniel Cooley, Arthur Tuttle, and Jon Clements were speakers/leaders in MA. In July 2012, the delayed fungicide program research plots at UMASS were toured and discussed at the annual summer fruit grower’s meeting. The concepts and strategies pertaining to scab management alternatives (SMA) were also presented at 9 grower twilight meetings by project scientists during April-June 2012. (approx. 30 attendees each). The project was also discussed at the Winter 2013 meeting of the Maine State Pomological Society. (60 attendees).

The New England Apple Scab Control Practices Survey

A survey was conducted in May-July 2012 to learn about current apple scab management in commercial apple orchards within New England. 507 growers were invited to take the survey and 115 responded. A report has been written by Renae Moran and will be web-published at http://extension.umass.edu/fruitadvisor/ and at comparable websites in ME and NH. In summary, growers reported use of at least one sanitation measure on 41% of acres, but only 15% of growers were doing a fall scab PAD index. The primary reasons for not doing a fall scab PAD were lack of time (37%) and lack of training (36%). Seventy nine percent of growers reported routine start of scab fungicide protection at Green Tip or Half inch Green bud stages, but 75% would consider delaying fungicide use with additional demonstration of effectiveness of delay strategy and training in methods that reduce scab risk such as sanitation and measuring the scab risk with a PAD index.

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