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Publication #ENY-624

2019–2020 Florida Citrus Production Guide: Pesticide Resistance and Resistance Management1

Lauren M. Diepenbrock, Megan M. Dewdney, Ramdas Kanissery2

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, and weeds of citrus creates a potent environmental stress. There are now many examples of pests, pathogens, and weeds 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. With repeated or intense exposure to herbicides, some weeds develop resistance because only individuals that are capable of detoxifying the chemical persist over time. A single resistance mechanism can sometimes provide defense against different classes of chemicals; 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.

Of the factors that affect the development of resistance, including 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 assuring 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 and 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 is also likely to be found in weeds with repeated exposure to certain herbicides. 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. In tangerine groves with Alternaria brown spot, resistance has been detected 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 resistance 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, but that susceptibility can be restored by rotating modes of action used in management programs. Resistance management is crucial to the management of this insect. Glyphosate-resistant weeds are becoming commonplace in many production systems with the repeated use of this popular pre-emergence herbicide, highlighting the need to rotate materials for weed management.

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 are separate tables for insecticides/ acaricides, 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/classificationofherbicidesiteofaction.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 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

2A

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

11A

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

21A

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

and salts

Aliette

Phostrol, ProPhyt

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

Table 3. 

Herbicides used in Florida citrus grouped by mode of action.

HRAC Group1

Group name / Chemical family

Common Name

Trade Name(s)

A

Aryloxyphenoxy-propionate

Cyclohexanedione

fluazifop-p-butyl

sethoxydim

Fusilade

Poast

C1

Triazine

Uracil

simazine

bromacil

Caliber, Princep, Simazine

Hyvar, Krovar

C2

Urea

diuron

Direx, Karmex, Krovar

D

Bipyridylium

paraquat

Gramoxone

E

N-phenyl-phthalimide Triazolinone

Pyrimidinedione

flumioxazin

carfentrazone-ethyl

saflufenacil

Chateau

Aim

Treevix

F1

Pyridazinone

norflurazon

Solicam

F2

Triketone

mesotrione

Broadworks

G

Glycine

glyphosate

(Various)

E.g., Roundup, Gly Star

K1

Dinitroaniline

oryzalin

pendimethalin

Surflan

Prowl

L

Alkylazine

indaziflam

Alion

1 Mode of action based on the 2018 Herbicide Resistance Action Committee (HRAC) Mode of Action Classification

Footnotes

1.

This document is ENY-624, one of a series of the Entomology and Nematology Department, UF/IFAS Extension. Original publication date December 1995. Revised May 2018 and March 2019. Visit the EDIS website at https://edis.ifas.ufl.edu for the currently supported version of this publication.

2.

Lauren M. Diepenbrock, assistant professor, Entomology and Nematology Department; Megan M. Dewdney, associate professor, Plant Pathology Department, UF/IFAS Citrus Research and Education Center; and Ramdas Kanissery, assistant professor, weed science, Agronomy Department, UF/IFAS Southwest Florida REC; 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.