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Publication #ENY-624

2018–2019 Florida Citrus Production Guide: Pesticide Resistance and Resistance Management1

L. M. Diepenbrock and M. M. Dewdney2

Populations of animals, fungi, bacteria, and plants possess the ability to respond to sustained changes or stresses in their environment in ways that enable the continued survival of the species. Such environmental stresses include physical factors (e.g. temperature or humidity), biological factors (e.g., predators, parasites, or pathogens) and environmental contaminants. In any population, a small percentage of individuals will be better able to respond to new stresses because of unique traits or characteristics that they possess. Consequently, those individuals will survive, reproduce, and become more common in a population. This phenomenon is commonly referred to as “survival of the fittest.”

Many pest species, such as the citrus rust mite, are exceptionally well-equipped to respond to environmental stresses because of their short generation time and large reproductive potential. The use of chemical sprays to control insect, mite, bacterial, and fungal diseases of citrus creates a potent environmental stress. There are now many examples of pests and pathogens that have responded by developing resistance to one or more pesticides. Pesticide-resistant individuals are those that have developed the ability to tolerate doses of a toxicant that would be lethal to the majority of individuals. The resistance mechanisms can vary according to pest species and/or the class of chemical to which the pest is exposed. Resistance mechanisms include an increased capacity to detoxify the pesticide once it has entered the pest’s body, a decreased sensitivity of the target site that the pesticide acts upon, a decreased penetration of the pesticide through the cuticle, or sequestration of the pesticide within the organism. The main resistance mechanism for fungal pathogens is a change in the target site so that the pathogen is less susceptible or fully resistant. A single resistance mechanism can sometimes provide defense against different classes of chemicals and this is known as cross-resistance. When more than one resistance mechanism is expressed in the same individual, this individual is said to show multiple resistance.

Because the traits for resistance are passed from one generation to the next, continued stress from a pesticide may, over time, create resistance in the majority of individuals in a population. From an operational perspective, this process would be expressed as a gradual decrease and eventual loss of effectiveness of a chemical. Resistance to a particular chemical may be stable or unstable. When resistance is stable, the pest population does not revert to a susceptible state even if the use of that chemical is discontinued. When resistance is unstable and use of the chemical is temporarily discontinued, the population will eventually return to a susceptible state, at which time the chemical in question could again be used to manage that pest. However, in this situation, previously resistant populations are likely to show resistance again.

Of the factors that affect the development of resistance, which include the pest’s or pathogen’s biology, ecology and genetics, only the operational factors can be manipulated by the grower. The key operational factor that will delay the onset of pesticidal resistance and prolong the effective life of a compound is to assure the survival of some susceptible individuals to dilute the population of resistant individuals. The following operational procedures should be on a grower’s checklist to steward sound pesticidal resistance management for acaricides, insecticides, fungicides, and herbicides:

  1. Never rely on a single pesticide class.

  2. Integrate chemical control with effective, complementary cultural and biological control practices.

  3. Always use pesticides at recommended rates and strive for thorough coverage.

  4. When there is more than one generation of pest, alternate different pesticide classes.

  5. Do not use tank mixtures of products that have the same mode of action.

  6. If control with a pesticide fails, do not re-treat with a chemical that has the same mode of action.

Reports of resistance have been documented for certain acaricides used to control citrus rust mite and fungicides used to combat diseases in Florida. Resistance to Benlate developed in the greasy spot fungus shortly after the product was introduced about 30 years ago and is still widespread. Benlate resistance also occurs in the scab fungus in isolated situations and is stable. Resistance has been detected in tangerine groves with Alternaria brown spot to strobilurin fungicides (Abound, Gem, and Headline and contained in the mixtures Pristine, Priaxor and Amistar Top) but no resistance has developed to ferbam. Dicofol resistance in citrus rust mite was detected throughout the citrus industry about 10 years ago, but resistance proved

to be unstable and usage of dicofol has continued. Agri-mek tolerance in citrus rust mite is of concern and growers should follow sound resistant management practices when using this product. Recent studies have shown reduced susceptibility to several insecticides in populations of Asian Citrus Psyllid after repeated exposure to similar materials and that susceptibility can be restored by rotating modes of action used in management programs. Resistance management is crucial to the management of this insect.

The following tables are provided to aid in the rotation of pesticides with different modes of action within a season or from year to year. There is a separate table for insecticides/acaricid- es, fungicides, and herbicides. The information in these tables was derived from information produced by the Insecticide Resistance Action Committee (IRAC) (http://www.irac-online.org/), Fungicide Resistance Action Committee (FRAC) (http://www.frac.info/) and the Herbicide Resistance Action Committee (HRAC) (http://hracglobal.com/pages/classificationofher-bicidesiteofaction.aspx). Each table lists the number (or letter in the case of herbicides) of the group code for each pesticide class, the group name or general description of that group of pesticides, the common name of pesticides used in citrus production that belong to each group and examples of trade names of pesticides for each common name listed. When using the table to rotate between using products with different modes of action, choose products with a different group code than previously used in the grove during the current growing season. In the case of insecticides/acaricides, many of these pesticides are broken into subgroups. It is unclear whether cross-resistance will occur between these subgroups. When possible, it is recommended to rotate with an entirely different group. (Note: The IRAC and FRAC mode of action systems both use a similar numbering system. There is no cross-resistance potential between the insecticides and fungicides.) Products with broad- based activity such as sulfur, copper, and oil are not included in this list because the development of resistance to them is not likely.

Tables

Table 1. 

Insecticides and miticides used in Florida citrus grouped by mode of action.

IRAC Group1

Subgroup

Group Name

Common Name

Trade Name

1

1A

Carbamates

carbaryl oxamyl

Sevin Vydate

1

1B

Organophosphates

acephate chlorpyrifos dimethoate malathion methidathion naled phosmet

Orthene Lorsban Dimethoate Malathion Supracide Dibrom Imidan

2

 

Cyclodiene Organochlorines

endosulfan

Phaser

3

3A

Pyrethroids

bifenthrin fenpropathrin zeta-cypermethrin

Brigade Danitol Mustang

4

4A

Neonicotinoids

acetamiprid clothianidin imidacloprid thiamethoxam

Actara, Assail, Admire Pro, Advise, Alias, Belay, Couraze, Imida E-Ag, Impulse, Macho, Montana, Nuprid, Pasada, Platinum, Prey, Torrent, Widow

 

4D

Butenolides

flupyradifurone

Sivanto

5

 

Spinosyns

spinosad

spinetoram

Spintor

Delegate

6

 

Avermectins

abamectin

Abacus, Abba, Agri-mek, Clinch, Epi-mek, Reaper, Zoro

7

7A

Juvenile Hormone Analogues

methoprene

Extinguish Ant Bait

7B

Fenoxycarb

fenoxycarb

Precision

7C

Pyriproxyfen

pyriproxyfen

Knack

10

10A

Hexythiazox

hexythiazox

Savey

11

 

Bacillus thuringiensis (B.t.)

B.t. var. aizawai

B.t. var. kurstaki

Various

Various

12

12B

Organotin miticides

fenbutatin oxide

Vendex

12C

Propargite

propargite

Comite

15

 

Benzoylureas

diflubenzuron

Micromite

16

 

Buprofezin

buprofezin

Applaud

18

 

Diacylhydrazines

methoxyfenozide

Intrepid

21

 

METI acaricides

pyridaben fenpyroximate

Nexter Portal

23

 

Tetronic/Tetramic acid derivatives

spirodiclofen spirotetramat

Envidor Movento

28

 

Diamides

chlorantraniliprole

Exirel, Verimark, Voliam Flexi (one component)

UN

 

Unknown MOA

bifenazate

Acramite

 

cryolite

Kryocide

 

dicofol

Kelthane

1 Mode of action based on the Insecticide Resistance Action Committee (IRAC) Mode of Action Classification V8.4 (2018)

Table 2. 

Fungicides used in Florida citrus grouped by mode of action.

FRAC Group1

Group Name

Common Name

Trade Name

1

MBC—fungicides

(Methyl benzimidazole carbamates)

thiabendazole

Many (TBZ)

3

DMI—fungicides (Demethylation inhibitors)

difenoconazole fenbuconazole imazalil propiconazole

Amistar Top Enable Many

Banner Maxx, Bumper, Orbit, Propimax

4

PA—fungicides (Phenylamides)

metalaxyl mefenoxam

Ridomil

Ultraflourish, Ridomil Gold, Subdue

7

SDHI—fungicides

(Succinate-dehydrogenase inhibitors)

boscalid fluopyram fluxapyroxad

Pristine

Luna Sensation Priaxor Xemium

11

QoI—fungicides

(Quinone outside inhibitors)

azoxystrobin trifloxystrobin pyraclostrobin

Abound, Graduate A+, Amistar Top Gem

Headline, Pristine

12

PP—fungicides (Phenylpyrroles)

fludioxonil

Graduate, Graduate A+

40

CAA—fungicide (Carboxylic acid amides)

mandipropamid

Revus

43

Benzamides

Fluopicolide

Adorn, Presidio

M03

Dithiocarbamates

ferbam

Ferbam Granuflo

M01

Inorganic

copper

Many

P07

Phosphonates

fosetyl-Al phosphorous acid

Aliette

Phostrol, ProPhyt

1 Mode of action based on the Fungicide Resistance Action Committee (FRAC) 2018.

Table 3. 

Herbicides used in Florida citrus grouped by mode of action.

HRAC Group1

Group Name

Common Name

Trade Name

A

FOPs DIMs

fluazifop-p-butyl clethodim sethoxydim

Fusilade

Prism, Select, Volunteer Poast

C1

Triazine Uracil

simazine bromacil

Princep, Sim-Trol Hyvar, Krovar

C2

Urea

diuron

Direx, Karmex, Krovar

D

Bipyridylium

diquat paraquat

Reglone-Dessicant Gramoxone

E

Diphenylether

N-phenylphthalimide Triazolinone

oxyfluorfen flumioxazin carfentrazone-ethyl

Galigan, Goal, Oxiflo Chateau, Suregard Aim

F1

Pyridazinone

norflurazon

Solicam

G

Glycine

glyphosate

Many (Roundup)

K1

Dinitroaniline Pyridine

oryzalin pendimethalin trifluralin thiazopyr

Surflan, Oryza Pendulum, Prowl Treflan, Snapshot Mandate

L

Benzamide

isoxaben

Gallery, Snapshot

N

Thiocarbamate

EPTC

Eptam

Z

Organoarsenical

MSMA

MSMA-6

1 Mode of action of herbicides based on the Herbicide Resistance Action Committee (HRAC) 2005.

Footnotes

1.

This document is ENY-624, one of a series of the Department of Entomology and Nematology, UF/IFAS Extension. Original publication date December 1995. Revised May 2018. Visit the EDIS website at https://edis.ifas.ufl.edu for the currently supported version of this publication.

2.

L. M. Diepenbrock, assistant professor, Department of Entomology and Nematology; and M. M. Dewdney, associate professor, Plant Pathology Department, Citrus Research and Education Center; UF/IFAS Extension, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other products of suitable composition. Use pesticides safely. Read and follow directions on the manufacturer's label.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.