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 2012 grower survey, published in 2013, defined current apple scab management practices and charted the course of collaboration for project scientists and growers in MA, NH, and ME. Scientists assisted growers with potential ascospore dose (PAD) assessments during Fall 2012 and with sanitation methods (urea application and leaf-chopping) between leaf fall 2012 and the green tip bud stage in Spring 2014 at university orchards in all states and at a total of 17 commercial sites. At the 11 orchards which had low enough scab levels to “pass” the PAD assessment in the Fall, the 1^st scab spray the following Spring was delayed until the pink bud stage or later. This was done successfully in almost all cases. At the 9 orchards that “failed” the Fall PAD, the sanitation methods were performed without the delays in the spring fungicide spray programs. In most cases, sanitation reduced scab levels in blocks of apple trees as compared to un-sanitized blocks of trees. The season was unusually dry from green tip through pink: there were no infection periods during this interval. For this reason, spraying in some blocks of trees was delayed until bloom to give these scab management alternatives (SMA) a more rigorous challenge. Decision-support for tracking infection risk and making pesticide recommendations was provided by project scientists and weather-based support tools (NEWA and Orchard Radar). Project concepts, methods, and results were presented and discussed at grower workshops and meetings. Additional orchards entered the project in Fall 2013.

Objectives/Performance Targets

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 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

Under the guidance of UMass scientists, the 1^st scab spray was delayed in apple blocks until the pink bud stage in Spring 2013 at 5 sites in MA, CT, VT, and southwest NH. Test blocks also received urea applications and leaf-chopping. These sites had low enough levels of scab infestation to pass a PAD assessment in Fall 2012. 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 below the economic injury level. There was no rainfall between the green tip and pink bud stages and therefore no infection periods. Because of this, the differences between test blocks and control blocks were fewer than expected. However, 4 of the growers who delayed their 1^st sprays until the pink bud stage and started spraying their control blocks earlier and averaged 9 days of delay between the test blocks and the control blocks. At 6 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 leaf-chopping. 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 2 of the sites, there was less scab in the test blocks compared to the control blocks. At 4 sites the amounts were not different. PAD assessments were done on 1 or more blocks at all sites and a few new sites in Fall 2013 to prepare for the 2014 season. A 12^th grower, new to apples and struggling with scab, is being trained to increase sanitation and use diseases forecasting models.

At the UNH research farm, sprays in 4 blocks of apples trees were delayed until full bloom, sprays in 3 blocks were delayed until tight cluster, and 4 blocks (controls) were given a standard protectant program starting at green tip. All blocks received urea and flail leaf chopping in the Fall of 2012. The bloom sprays were delayed 35 days and the tight cluster sprays were delayed 10 days as compared to the control blocks. There was 1 infection period prior to bloom. In 2 of the comparisons, there was more fruit scab in the trees that were delayed until bloom than in the controls. In the other 2, the amount of scab was not different. UNH scientists also worked with 5 commercial growers. One of them delayed successfully until late pink and had no scab on leaves in July or on fruit in September. Three growers performed the sanitation strategies, after failing the PAD in Fall 2012. Levels of scab were low in July and September and all 3 passed the PAD in Sept. At least 2 of them will delay in 2014. A fifth grower, who has a great deal of scab, is being advised on sanitation and timing of sprays.

At the UME research farm, 3 blocks of apples trees were delayed until bloom (a delay of 11 days), 3 were delayed until tight or open cluster (a delay of 5 days), and 3 (controls) were sprayed from green tip on (no delay). In 8 of the 9 blocks, the amount of scab was very low in the PADs each year, the July leaf counts, and the September fruit counts. Scab management was very successful and there were no differences among treatments. In the 9^th block, there was 4.2% fruit scab in the section that was delayed until bloom, 0.8% in the section delayed until open cluster, and 0% in the control. UME scientists also worked with 3 commercial growers. These all had very low PAD counts going into the study. Each had a delayed block (delayed 20 days) and a control block. All 3 had very low amounts of scab in leaves and fruit in delayed blocks as well as control blocks (no differences). All 3 also passed the PAD assessments in Fall 2013.

In most of the research sites in 2013, there were no infection periods before the pink bud stage. For this reason, the UNH and UME scientists pushed one of the treatments at some of the sites to a “delay until full bloom 1^st spray”. One infection period occurred between pink and bloom. UMass growers were not willing to change the protocol and wait that long. This was reasonable as a similar dry spell in Spring 2012 resulted in a massive infection period at bloom and some scab problems. For both 2012 and 2013, the scab management alternative strategies of this study did not get challenged as vigorously as planned in this study. In an average year, there would be 2-3 infection periods before the pink bud stage. We hope 2014 will have more typical weather.

Growers in this study have 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. All of the growers routinely check for scab forecasting from one of these sources and many have 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 for spore-trapping and maturation assessment during primary scab season and adjustments for dry periods. We need to more accurately predict the beginning and end of scab season.

In Fall 2013 all the grower sites were re-visited and another round of PAD assessments were performed, many with the growers, to prepare for the 2014 season. Three additional orchards were added to the study in MA. Sanitation strategies were planned with all growers. Plans for delayed 1^st scab spray and/or leaf sanitation experiments are underway for 2014 in all 3 states. Spray application records are being collected from all cooperating growers in the study. Pesticide usage will be compared between experimental treatments and their controls.

Impacts and Contributions/Outcomes

Groups of apple growers were educated in scab management alternatives (SMA) at two grower meetings in 2013: one each MA (Oct.) (45 attendees) and ME (Aug.) (~40 attendees). The sessions included the delayed 1^st spray strategy, sanitation strategies, reduced-risk fungicides, potential ascospore dose assessments (PAD), and use of decision support tools, such as NEWA and Orchard Radar. William MacHardy was the featured speaker in ME. Arthur Tuttle spoke in MA. The concepts and strategies pertaining to scab management alternatives (SMA) were also presented at 5 grower twilight meetings, and at the eIPM Stakeholder’s Meeting at Ward’s Berry Farm by UMass project scientists during April-June 2013. (approx. 30 attendees each). UME scientists presented project ideas, strategies, and results at the Maine Agricultural Trades Show (Jan.), at the Preseason Tree Fruit Meeting (Mar.), and at the UME Highmoor Farm Summer Tour (July), the Great Maine Apple Day (Oct.), the NH Risk Management Meeting (Nov.), and at a Pesticide Applicator Training Session (Nov.). UNH scientists presented project ideas, strategies and results at 2 additional twilight meetings (April and June). In all 3 states, project scientists worked with cooperating growers and their staff to train them in scab management alternatives. These alternatives were also discussed in Spring issues of Healthy Fruit (http://extension.umass.edu/fruitadvisor), J. Clements, editor and in the Maine Tree Fruit Newsletter.

The New England Apple Scab Control Practices Survey

The survey that was conducted in May-July 2012 to learn about current apple scab management in commercial apple orchards within New England was published in Fall 2013 in Fruit Notes 78(4):9-11 (http://extension.umass.edu/fruitadvisor) . 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.

Publications:

2013. Moran, R. et al. Survey of New England Apple Growers on Using Sanitation and Delaying Early-season Fungicide Applications. Fruit Notes 78(4): 9-11.

2013. Cooley, D. et al. Increasing Fungicide Use in New England Apples. Fruit Notes 78(4): 1-6.

2013. 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.

Collaborators: