Pesticide Risk Reduction Program
Pest Management Centre
Reduced-Risk Strategy for Apple Scab Management
For inquiries please contact:
Pesticide Risk Reduction Program
Pest Management Centre, AAFC
pmc.cla.info@agr.gc.ca
March 2014
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Preface
Pesticide risk reduction strategies are developed under the Pesticide Risk Reduction Program (PRRP), a joint
program of Agriculture and Agri-Food Canada (AAFC) and the Pest Management Regulatory Agency (PMRA)
of Health Canada. The key objective of the program is to reduce the risks to the environment and to human
health from pesticide use in agriculture. To achieve this objective, the PRRP works with grower groups,
industry, provinces, and researchers to identify gaps in pest management and opportunities for pesticide
risk reduction, and to develop and implement strategies to address these.
A pesticide risk reduction strategy is a detailed plan that aims to address grower needs for reduced-risk
management tools and practices for specific pest issues. The strategies are developed through extensive
consultation with stakeholders. The strategy document presented here summarizes the framework and
activities supported by the PRRP. It is intended to provide an update on the progress in developing and
implementing the strategy and new tools and practices made available through this process.
For more information, please visit the www.agr.gc.ca/pmc.
Acknowledgement
The Pesticide Risk Reduction Program acknowledges all participating stakeholders for their contribution and
collaboration in the development and implementation of this reduced-risk strategy for apple scab
management.
1. Executive Summary
This document reports on the collaborative development of a reduced-risk strategy for control of apple scab
management in orchards across Canada. The strategy is a national initiative developed with industry
stakeholders and with the support of the federal government. The objective of the strategy is to minimize
the need for using fungicides to control apple scab while promoting viable disease management and farm
profitability.
The pesticide risk reduction strategy includes the identification of potential pesticide risks, knowledge gaps
and barriers to the adoption of reduced-risk management practices, potential reduced risk solutions for
these issues, goals and milestones, a strategic action plan and information on progress of the activities
implemented to support the strategy.
Within the context of the strategy, pesticide risks and pest management issues were identified by an expert
working group. One of the core issues raised by the group members was the development of resistance to
commonly used fungicides among apple scab pathogen populations. This issue was addressed by identifying
areas where new knowledge and practices were needed, initiating projects to generate the knowledge and
to support the development of practices, and disseminate the information to growers.
Overall, the strategy addresses three main goals with identified targets, milestones, and activities: i)
development and implementation of alternative strategies for apple scab management, ii) Facilitate the
adoption of bio-fungicides, and iii) Improve adoption of resistance management strategies.
Since 2006, AAFC's Pest Management Centre has funded six risk reduction projects to support the
implementation of apple scab strategy. One project facilitated the testing of a microbial control agent
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(Microsphaeropsis ochracea) that lowers the amount of overwintering inoculum of apple scab pathogen.
Another has advanced the development of an in vitro method, which evaluates the efficacy of fungicides
against pathogen ascospore samples in order to determine whether the pathogen population shows
resistance to fungicides. A grower's guide including information on the biology of the apple scab pathogen
and approaches for management of primary and secondary infections was developed and published online.
A national survey was also conducted to document the spread of pathogen resistance to sterol inhibitors and
strobilurins fungicides. As an outcome, a commercial service is now offered to growers by the University of
Guelph where leaf samples can be tested to determine the level of pathogen resistance to various fungicides
in individual orchards.
It is anticipated that the use of the knowledge and tools developed through this strategy will help growers in
adopting sustainable apple scab management in their orchards.
2. Introduction
Apples are produced across Canada on a total area of 17,000 hectares. The main regions are Ontario
(37%), Quebec (29%), British Columbia (21%), and the Maritimes (12%).
In Canada, apple scab is the most serious disease of apple and is a significant economic threat in all
growing regions. Caused by the pathogenic fungus Venturia inaequalis it is of particular importance in
Eastern Canada, as infection and disease spread are favored by cold winters and wet growing conditions. In
these areas the disease occurs every year and often causes significant economic losses, both directly from
fruit infections (which affect yield, fruit quality and storability) or indirectly from defoliation (which affects
tree vigor and winter survival). If not controlled, apple scab can result in 100% crop loss in any given year.
In BC, where the weather is usually dryer, the disease is less serious although it could be significant in
certain growing areas in the interior parts of the province.
3. Pest Management and Pesticide Risk Issues
Chemical control of apple scab by fungicides is the most common method of controlling this disease on
commercial cultivars. Some fungicides have protectant activity, which inactivates and kills fungal spores and
prevents infection. Some have eradicant activity which prevents or reduces further growth of infections that
have already started. All pesticides used, sold, or imported into Canada, are regulated by Health Canada's
Pest Management Regulatory Agency (PMRA).
Cultural practices are also used for apple scab management. These include scab-resistant cultivars (Belmac,
Britegold, Macfree, Moira, Murray, Nova Easygro, Novamac, Novaspy, Primevere, Richelieu, Rouville and
Trent), and sanitation by means of tree pruning and removal of leaf litter to physically reduce fungal
inoculum in the orchard. As the pathogen overwinters in the dead leaves on the orchard floor, destruction of
the leaf litter by burning or flail-mowing contributes to the reduction of primary inoculum in the next
growing season. Urea applications between the growing seasons also contribute to the reduction of primary
inoculum.
Several of the newer fungicides registered in Canada for apple scab pose medium to high risk for resistance
development. If used repeatedly, these products are at risk of losing their efficacy over time. Resistance in
V. inaequalis populations and lack of efficacy for some of the fungicides (e.g. strobilurins and sterol
inhibitors) has been already observed over the years in some orchards.
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Resistance development often results in increased fungicide use, as more frequent applications are required
to compensate for the reduced efficacy, which increases production costs and environmental concerns.
Overall, successful management of apple scab must address various challenges due to the endemic nature
of the disease, variable environmental conditions, potential removal of some pesticides following reevaluation by PMRA, potential development of pathogen resistance to fungicides, and high apple quality
standard demanded by consumers.
The apple scab strategy is thus centered on the development of reduced risk tools and practices to
determine appropriate timing and need for fungicide applications, with the goal of minimizing unnecessary
fungicide sprays and managing pathogen resistance to fungicides.
4. Reduced Risk Management Strategy for Apple Scab
Apple scab was identified as a priority issue for apple growers through consultations between AAFC’s
Pesticide Risk Reduction Program and the Canadian Horticultural Council's (CHC) Apple Working Group, a
subgroup of the CHC’s Apple and Fruit Committee. A new working group was established in 2006 under the
PRRP that included researchers, growers’ reps, provincial specialists, and other stakeholders and tasked
with the development of the strategy. Recommendations generated through working group consultations
were captured in the strategy’s Action Plan and activities to address identified gaps were carried out through
the support of various projects. Specific issues identified in the process of consultations are outlined below.
4.1 Issues and needs for apple scab management
The apple scab working group identified the issues facing apple growers in coping with the disease. The
following is a list of the most important issues brought forward through discussions with the working group.
Some of these issues were addressed within the context of this strategy; others, in particular #6, are to be
pursued through other channels available to the industry.
1.
2.
3.
4.
5.
6.
Registration of new and effective low-risk products
Knowledge and management of pathogen resistance to fungicides
Develop new cultural control options
Improve timing of fungicide applications
Reduction of overwintering pathogen inoculum
Replacement of susceptible apple cultivars with resistant ones
5. Apple Scab Pesticide Risk Reduction Action Plan
Based on the information collected through consultations with the apple scab working group, an action plan
has been developed (Table 1). The plan outlines the goals of the strategy, the targets and the milestones,
as well as the activities supported over the course of the strategy (2006-2014).
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Table 1: Action plan for reduced risk apple scab management (status February 2014)
Strategy Goal #1
Target
Develop a
management plan
to reduce
overwintering
inoculum
Develop and
implement
alternative
strategies for
apple scab
management
Use of practices
that maximize
sprayer efficacy
Develop and
encourage the use
of prediction tools
Improve grower
knowledge and
adoption of newly
introduced tools
and methods
Milestones
Assess efficacy of a new
microbial agent
Develop information on
cultural practices for crop
residue management
Completed
X
X
Activities
Work conducted through AAFC project BPI06-030 and focused on testing a novel biocontrol
agent, Microsphaeropsis ochracea. Results indicate potential reduction in inoculum levels of
apple scab in the field.
Work conducted through AAFC project PRR05-050. A guide on Apple scab: improving
understanding for better management was published on AAFC’s website and made
available to growers. It demonstrates the use of various cultural techniques, such as flailmowing and urea applications in the fall, to lower scab inoculum.
Encourage annual pruning to
optimize spray coverage
Outreach activities outside the scope of the strategy may be required (e.g. demonstrations,
presentations, workshops, factsheets).
Incorporate sequential
sampling into IPM system
Work conducted through AAFC project BPI06-030. The use of a sequential sampling plan
allowed a pesticide use reduction of 24% and 45% at two apple orchards in Quebec,
respectively, as compared to the standard conventional practice. The Apple scab: improving
understanding for better management guide which includes information about sequential
sampling plan, was made available to growers in Quebec and Ontario.
X
Promote the use of apple
scab forecasting software
Growers in some regions, primarily in Quebec, are using RIMpro forecasting software. The
technology is posted on the web and is available to all growers.
Develop and disseminate a
guide on apple scab
management
As part of project PRR05-050, the Apple scab: improving understanding for better
management guide can be downloaded from the PMC homepage and St-Jean-sur-Richelieu
homepage. The guide was presented to growers and advisors at various grower meetings in
Quebec and Ontario.
X
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Strategy Goal #2
Facilitate the
adoption of new
bio-fungicides
Strategy goal #3
Target
Milestones
Timorex Gold and
Regalia adoption
Evaluate Timorex Gold and
Regalia for use in apple scab
management
Microsphaeropsis
ochracea adoption
Target
Develop methods
to reduce
development of
pathogen
resistance in
orchards
Improve adoption
of resistance
management
strategies
Improve grower
awareness of
resistance
management for
apple scab
Enable growers to
test for fungicide
resistance in their
orchards
Completed
X
The biocontrol agent is licensed to the German company Prophyta, currently a unit of Bayer
CropScience. Sufficient level of efficacy in the field, however, still needs to be demonstrated
for a European registration. In Canada, further work towards the registration of M. ochracea
for apple scab management is currently considered low priority by the working group.
Registration submission
Milestones
Develop thresholds for
summer sprays and refine
the spray approach
Activities
Field trials to evaluate the efficacy of Timorex Gold and Regalia, when used in an integrated
management plan for apple scab, were conducted in New Brunswick, Quebec, and Ontario,
through AAFC project BPI09-060. The use pattern of the two products was found to be
ineffective for apple scab control under the conditions of the trials.
Completed
X
Activities
Work conducted through AAFC project PRR06-910. A refined summer spray approach
contributed to lowering pesticide residues on fruit by reducing the number of targeted
fungicide applications and increasing their effectiveness.
Develop a tool to evaluate
the level of resistance in
fungal populations
X
Work conducted through AAFC project PRR06-920. An in vitro method was developed to
evaluate the efficacy of fungicides against ascospore samples harvested from leaves of
infested orchards. A delivery agent or mechanism is required to implement at the farm level.
Develop and publish a guide
on resistance management
X
The guide Apple scab: improving understanding for better management developed
under project PRR05-050, includes a section on resistance management.
Inform growers on apple
scab resistance development
X
Work conducted through AAFC project PRR06-920. Presentations at grower meetings served
to promote fungicide resistance monitoring. Information on development of fungicide
resistance was also made available through the Quebec agriculture warning network.
X
Project PRR11-060 was initiated in 2011 to document the extent of apple scab resistance to
systemic fungicides, including sterol inhibitors and strobilurins, in apple orchards. Led by
Ontario Apple Growers, the survey involved all apple growing regions in Canada. The survey
confirmed the presence – and revealed new trends – of resistance development to these
fungicide groups. As an additional outcome, a new established testing protocol is now offered
to growers as a commercial service by the University of Guelph’s Pest Diagnostic Laboratory
(PDL) where leaf samples sent to the lab can be tested to determine the level of pathogen
resistance to various fungicides in individual orchards. Provincial results of the 2011 field
season of the apple scab resistance survey in Ontario were published by Ontario Ministry of
Agriculture and Food. A new factsheet ‘Resistance of apple scab pathogen to fungicides in
Canadian Orchards: Knowing and managing the risk’ is under development to disseminate
results from the national resistance survey to stakeholders.
Conduct a national survey of
resistance to fungicides;
develop advanced testing
protocols
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6. Strategy progress
The goals outlined below have been actively pursued since 2006.
6.1 Goal #1: Development and implementation of alternative control
strategies
The Pesticide Risk Reduction Program supported the development and publication of a manual,
titled "Apple scab: improving understanding for better management", written by Dr. Odile
Carisse. This document contains information on the biology of the apple scab pathogen and
recommendations on integrated management of the primary and the secondary infections. It
provides information on cultural practices and preventive approaches, such as using resistant
cultivars. The guide suggests the use of fall sampling plans, which can help forecasting disease
pressure for the following year and reduce the number of fungicide sprays in cases of low disease
pressure. Other parts of the manual are dealing with fungicide resistance management.
Reduced risk alternatives, such as biocontrol agents, were identified as potential tools to help in
resistance management and to be part of the control toolkit in case older fungicides would be
lost due to re-evaluation. Dr. Odile Carisse (Agriculture and Agri-Food Canada, St. Jean-surRichelieu, QC) and her team had discovered and studied a microbial pest control agent
(Microsphaeropsis ochracea) which could lower the level of overwintering inoculum in the
orchards. With the reduction in pathogen inoculum, it was demonstrated that the first chemical
fungicide application may be delayed in the spring and potentially reduce the overall number of
fungicide applications required per season. Workshops were held in Ontario and Quebec to
inform growers about the efficacy of M. ochracea and the potential of integrating it into an IPM
system in the event that it becomes available commercially.
6.2 Goal #2: Facilitate the adoption of bio-fungicides
The Pesticide Risk Reduction Program supported field tests with Timorex Gold, a reduced-risk,
broad spectrum fungicide derived from tea tree oil, to evaluate its efficacy in controlling the
disease. The Program also supported field tests with Regalia, a biofungicide designed to activate
the plant’s natural defenses to protect against a variety of fungal and bacterial diseases. These
trials were conducted in apple growing areas in three provinces (ON, QC, NB). While results
indicated inefficacy for apple scab control, Timorex Gold has been registered in Canada to
control/suppress other diseases on other crops.
6.3 Goal #3: Improve adoption of fungicide resistance management
strategies
Vincent Philion, a researcher from the "Institut de Recherche et de Développement en
Agroenvironnement" in Quebec, developed an in vitro method to evaluate the efficacy of
fungicides on samples of the pathogen’s ascospore collected from leaves in infected orchards.
This tool could help growers determine if pathogen populations in their orchard show resistance
to various control products. This, in turn, could allow for improved selection of fungicides for
individual orchards.
The same team has also developed a fungicide spray action threshold to help minimize the use of
captan for summer management of scab. A refine summer spray approach could contribute to
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lower the risk of resistance development, as the fungicide applications are expected to be fewer
and more effective.
The guide by Dr. Carisse contains a section on resistance management for apple scab and makes
references to the state of resistance in Quebec orchards.
A 2-year national apple scab fungicide resistance testing project launched in 2011 elucidated the
spread of pathogen resistance in apple-producing regional of Canada. The project also led to the
establishment of a commercial standard protocol for apple scab fungicide resistance test which is
being offered to growers as a diagnostic service since 2013 for a fee. The service enables
growers to send leaf samples and obtain an indication about the status of pathogen’s resistance
to a range of fungicides in their orchards. This new tool allows for better decisions regarding the
use of fungicides, including tank mixes, timing, and number of applications.
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