Publication 360, Guide to Fruit Production:
Resistance Management Strategies


Excerpt from Publication 360, Guide to Fruit Production, 2012-13
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Cover of Publication 360, Fruit Production RecommendationsTable of Contents

  1. Resistance Management Strategies
  2. Other information on pest resistance:
  3. Chapter 12 - Managing Pest Resistance (PDF 119 kb)
  4. Related Links

Resistance management strategies

General resistance management strategies:

  • Follow an integrated pest management program that makes use of a variety of different pest control strategies including monitoring and crop rotation, biological, and chemical control options.
  • Spray only when necessary. Use established thresholds where available.
  • Spray at the best timing for the pest and the product you are using.
  • Apply registered products as directed, with a well calibrated sprayer.
  • Read the product label. New products include resistance management recommendations on the label.
  • Know the active ingredient of a pesticide. Many chemicals with the same active ingredients are marketed under different brand names. For example, the insecticide permethrin is marketed under the brand names Pounce and Perm-Up.
  • Know the mode of action. Different chemicals may also have the same mode of action. For example, both Assail and Admire have the same mode of action. To use Assail after Admire is equivalent to using Assail after Assail, since resistance to both chemicals develops at the same time. This can happen even if only one has been used repeatedly.

For a list of chemical groups and their modes of action, see Table 12-2. Fungicide/Bactericide Groups Based on Sites of Action, and Table 12-3. Insecticide and Miticide Groups Based on Sites of Action.

Managing resistance to fungicides

  • Rotate products from different chemical groups. Do not exceed the recommended number of applications per season or sequential applications of a pesticide or group of pesticides.
  • Tank mix products from different families. This is an accepted resistance management strategy for fungicides. Use only registered tank mixes (specified on the label).
  • Apply fungicides before disease occurs. Follow disease prediction models when possible. Applications of fungicides after the disease is established are more likely to select for resistant populations of the pathogen.
  • Know which fungicides are combinations of chemicals from more than one fungicide group (e.g. Pristine, Switch). It is important to rotate these fungicides with products from different groups for all active ingredients in the combination.

Not all fungicides are prone to resistance. Most fungicides that affect a wide range of different metabolic processes in fungi are not prone to the development of resistance. These fungicides are known as multi-site inhibitors and are designated with an M in the group number (Table 12-2. Fungicide/Bactericide Groups Based on Sites of Action). These products can be applied to fungal pathogens repeatedly without rotation without significant risk of resistance development. Coppers and streptomycin are exceptions to this with respect to bacteria. For example, bacteria causing fire blight or blister spot can develop resistance to these products.

The strategy for preventing fungicide resistance depends on:

  • the resistance risk of the pathogen to a particular ­fungicide group
  • the availability of rotation options

Two components of a resistance management strategy for a fungicide group include:

  • the number of consecutive applications before rotating to a different family group
  • the maximum number of applications per season

In some cases, a single fungicide group can control more than one pathogen. In this case, the maximum number of consecutive and total applications per season should be based on the pathogen with the highest risk of developing resistance. For high-risk pathogens with fungicide options from many groups, rotation to a different group is recommended after a single application of a resistance-prone fungicide, although this is not necessarily required by the label. For pathogens controlled by few registered fungicide families, the recommendation is to use no more than two consecutive applications of a resistance-prone fungicide and then alternate to a different fungicide family. When a product contains active ingredients from more than one family, each application counts as a use for each family.

Resistance management strategies by fungicide group and disease for Ontario fruit crops

These strategies reduce the risk for resistance development, and may be more stringent than label guidelines. Solo products have one active ingredient. Combination products have more than one active ingredient and are indicated with an asterisk (*).

Group 3: Sterol biosynthesis inhibitors, demethylation inhibitors (Funginex, Indar, Nova, Nustar, Mission, Topas, Inspire, Jade)

  • Apple scab resistance to Nova and Nustar has recently been confirmed in Ontario. Avoid using these products in orchards with resistance.
  • For apple scab and for powdery mildew in berries, use no more than two consecutive applications then rotate to a different fungicide group; use fungicides from this group no more than four times per season.
  • For powdery mildew in grape and brown rot in stone fruit, use once and then rotate to a different group; use fungicides from this group no more than twice per season.

Group 7: Lance, Cantus, Pristine*

  • For botrytis grey mould in berries, use no more than two consecutive applications then rotate to a different fungicide group. No more than 30% of total fungicides applied per season should include a solo or mixture product from this group. See Group 11 for recommendations for Pristine use.
  • For powdery mildew in grape and brown rot in stone fruits use once and then rotate to a different group. Apply no more than twice per season as a solo or mixture product. See Group 11 for recommendations for Pristine use.
  • Avoid using Pristine in apple orchards with documented resistance to Group 11 fungicides.

Group 9: Scala, Vangard, Switch*

  • For apple and pear scab, use once then rotate to a different fungicide group. Use prebloom, no more than two applications per season.
  • For botrytis grey mould in berries, use once then rotate to a different fungicide group. No more than 30% of total fungicides applied per season should include a solo or mixture product from this group.
  • For botrytis bunch rot in grape and brown rot in stone fruit, use once then rotate to a different group. Use products from this group no more than twice per season.

Group 11: Strobilurins (Flint, Sovran, Cabrio, Pristine*, Tanos*)

  • Apple scab resistance to Flint and Sovran has recently been confirmed in Ontario. Avoid using these products in orchards with resistance.
  • For apple and pear scab, use no more than two consecutive applications then rotate to a different fungicide group. Use products from this group no more than three times per crop.
  • For botrytis grey mould in berries use no more than two consecutive applications then rotate to a different fungicide group. No more than 30% of total fungicides applied per season should include a solo product from this group or no more than 50% of total fungicides applied per season if using combination products.
  • For powdery mildew in grape and brown rot in stone fruit, use once and then rotate to a different group. Use fungicides from this group no more than twice per season as a solo or mixture product.

Group 12: Scholar, Switch*

  • For Botrytis control in berries, use no more than two consecutive applications then rotate to a different fungicide group. No more than 50% of total fungicides applied per season should include a product from this group.
  • For storage rots in tree fruit, do not make more than one post harvest application.

Group 13: Quintec

  • For powdery mildew in strawberries, use no more than two consecutive applications then rotate to a different fungicide group. No more than 50% of total fungicides applied per season should include a product from this group.
  • For powdery mildew in grape and stone fruits, use once and then rotate to a different group. Apply no more than twice per season.

Group 17: Elevate

  • For botrytis grey mould in berries, use no more than two consecutive applications then rotate to a different group. Do not use more than four times per season.
  • For botrytis bunch rot in grapevine and brown rot in stone fruits, use once then rotate to a different group. Do not use more than twice per season.

Group 43: Presidio

  • For grape downy mildew, tank mix with a labelled rate of another fungicide registered for downy mildew, but with a different mode of action. Use once then rotate to a different group. Do not use more than twice per season.

Group U8: Vivando

  • For grape powdery mildew, use once then rotate to a different group. Do not use more than twice per season.

Managing resistance to insecticides and miticides

  • Rotate products from different chemical groups. Avoid sequential applications or repeated use of any pesticide or group of pesticides.
  • For insects with discrete generations, manage each generation of an insect pest as separate units. Use products from a single chemical group to manage a given generation of a pest. If the pest emergence or activity for that generation is prolonged, apply a second application of the same product. This exposes each generation to only one chemical group. Rotate to another chemical group (or groups) for subsequent generations. If re-treatments are necessary for a particular generation, choose a product in that same group.
  • Avoid unnecessary or repeated applications of miticides and rotate between products in different chemical groups. Many labels limit the number of applications of a product to one per season. Consider a multi-year rotation of miticides, so that mites are not exposed to products with a similar mode of action more frequently that once every three to four years. The use of an annual preventative delayed dormant oil or summer oils may help to suppress mite populations and reduce the need for rescue miticides when numbers exceed the treatment threshold(s).
  • Applications should be timed and directed to contact the most susceptible life stage of the pest.
  • Avoid tank mixing different insecticides to manage a single pest as this increases the probability that the target pest population will develop multiple resistance. Alternating products, rather than tank mixing them, is the preferred strategy for insecticides and miticides.
  • Consider area-wide resistance management programs, especially for pests of more than one crop.

Resistance management strategies by insecticide group for Ontario fruit crops

Group 1A, 1B & 2A

  • Resistance to these older, broad spectrum insecticides has occurred in various fruit pest populations in Ontario. Documented cases include resistance to organophosphates in spotted tentiform leafminer on apples, obliquebanded leafrollers on apples and pears, pear psylla on pears and oriental fruit moth on peaches, nectarines, pears and apples. Research from the University of Guelph and Agriculture & Agri-Food Canada has recently documented resistance development to organophosphates in Ontario and Quebec codling moth populations in apples.

Group 3: Ambush, Decis, Matador, Perm-Up, Pounce, Ripcord, Silencer, Up-Cyde (pyrethroids)

  • Present status of spotted tentiform leafminer and pear pyslla resistance is unknown given that resistance in these pests has not been monitored since the early 1990s. Previous studies demonstrate that spotted tentiform leafminer adults became resistant to all pyrethroids in many orchards in Ontario when exposed to repeated applications of these chemicals. Pear pyslla resistance to pyrethroids has been documented in western North America and some pear orchards in the Niagara peninsula. Resistance may occur in other parts of the province. Documented cases of resistance in populations of obliquebanded leafroller on apples have been found.
  • The repeated use of pyrethroid insecticides (more than once per season) is discouraged because of the potential for further resistance development and because pyrethroids are toxic to beneficial insects and mites.

Group 4: Calypso

  • Documented cases of tolerance to the neonicotinoid, Calypso has been found in some codling moth populations in Ontario and Quebec. Research is ongoing to determine if resistance to Group 4 is developing in apples.

Group 18 : Confirm, Intrepid

  • Documented cross resistance between organophospate insecticides and the growth regulators, Confirm and Intrepid have been found in some obliquebanded leafroller and codling moth populations, respectively, in Ontario. Where resistance is suspected for obliquebanded leafroller or codling moth, do not use Group 18, 1A or 1B. Always use one group of insecticides within the generation and rotate insecticide groups between generations. Consult the apple calendar for the appropriate timing of these products.

Group 5, 11, 15 & 28

  • There are no documented cases of resistance in Ontario for fruit crops. Use the basic principles of resistance management to ensure that insecticides in these groups work well in the future. Resistance management strategies by miticide group for Ontario fruit crops

Group 6: Agri-Mek

  • There are no documented cases of resistant mite populations in Ontario to this group. Use resistance management principles. Apply this product early before threshold numbers are reached.

Group 10: Apollo

  • Isolated cases of mite resistance to Apollo have been found in Ontario. Resistance has occurred where Apollo has been applied repeatedly in one season, or applied too late in the season. To delay resistance to Apollo, do not use Apollo every year. Apply Apollo when the mite population is synchronous and in the first summer generation egg stage.

Group 20B, 21, & 25

  • There are no documented cases of resistant mite populations in Ontario. Use resistance management principles.

Group 23

  • There are no documented cases of resistant mite populations in Ontario. Use resistance management principles. These products work slowly so patient and careful monitoring is needed to asses the results.


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 25 June 2007
Last Reviewed: 10 May 2012