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2008 Florida Citrus Pest Management Guide: Pesticide Resistance and Resistance Management1
M.E. Rogers, L.W. Timmer and C.W. McCoy2Populations of animals 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 and reproduce. 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, and some fungal diseases of citrus pests creates a potent environmental stress. There are now many examples of pests 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 mechanisms of resistance 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. 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 may eventually show resistance again.
Of the factors that affect the development of resistance, which include the pest'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. Since Topsin is also a benzimidazole fungicide, isolates of fungi resistant to Benlate would also be resistant to Topsin. No resistance has developed to ferbam or strobilurin fungicides at this time, however, strobilurin fungicides (Abound, Gem, and Headline) have potential for resistance development. 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.
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/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://www.plantprotection.org/hrac/). 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
Aldicarb
Carbaryl
Oxamyl
Temik
Sevin
Vydate
1
1B
Organophosphates
Acephate
Chlorpyrifos
Dimethoate
Fenamiphos
Malathion
Methidathion
Naled
Phosmet
Orthene
Lorsban
Dimethoate
Nemacur
Malathion
Supracide
Dibrom
Imidan
2
Cyclodiene
Organochlorines
Endosulfan
Phaser
3
Pyrethroids
Bifenthrin
Fenpropathrin
Brigade
Danitol
4
Neonicotinoids
Acetamiprid
Imidacloprid
Assail
Admire, Advise, Alias, Couraze, Imida E-Ag, Impulse, Macho, Montana, Nuprid, Pasada, Prey, Torrent, Widow
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
9
Cryolite
Cryolite
Kryocide
10
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
12
12C
Propargite
Propargite
Comite
15
Benzoylureas
Diflubenzuron
Micromite
16
Buprofezin
Buprofezin
Applaud
18
Moulting disruptors
Azadirachtin
Neemix
21
METI acaricides
Pyridaben
Fenpyroximate
Nexter
Portal
23
Tetronic acid derivative
Spirodiclofen
Envidor
25
Bifenazate
Bifenazate
Acramite
UN
Unknown MOA
Dicofol
Kelthane
1Mode of action based on the Insecticide Resistance Action Committee (IRAC) Mode of Action Classification V4.2.1 (2005).
Table 2. Fungicides used in Florida citrus grouped by mode of action.
FRAC Group1
Group Name
Common Name
Trade Name
1
MBC - fungicides
benomyl
thiabendazole
thiophanate methyl
Benlate
Many (TBZ)
Topsin
3
DMI - fungicides
imazalil
propiconazole
Many
Banner Maxx, Bumper,
Orbit, Propimax
4
PA - fungicides
metalaxyl
mefenoxam
Ridomil
Ultraflourish, Ridomil
Gold, Subdue
11
QoI - fungicides
azoxystrobin
trifloxystrobin
pyraclostrobin
Abound
Gem
Headline
12
PP - fungicides
fludioxonil
Graduate
13
Phosphonates
Fosetyl-Al
Phosphorous acid
Aliette
Phostrol, ProPhyt
M
M2
ferbam
mancozeb
Ferbam Granuflo
ManKocide
M
M9
copper
Many
1Mode of action based on the Fungicide Resistance Action Committee (FRAC) 2003.
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
1Mode 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 Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Date first printed: December 1990. Date revised: November 2007. This publication is included in SP-43, 2008 Florida Citrus Pest Management Guide. A copy of this publication may be found at http://edis.ifas.ufl.edu/CG026. Please visit the EDIS Web site at http://edis.ifas.ufl.edu. For a copy of this handbook, request information on its purchase at your county extension office.2. M.E. Rogers, assistant professor, Entomology and Nematology Department; L.W. Timmer, professor emeritus, Plant Pathology Department; and C.W. McCoy, professor emeritus, Entomology and Nematology Department; Citrus REC, Lake Alfred, Florida; Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 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 does 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 extension publications, contact your county Cooperative Extension service.
U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
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