Agriculture: Citrus Pest Management Guidelines

General Properties of Fungicides Used in Citrus

Common name
(Example trade name)
Chemical class Activity Mode of action
(group number)1
Resistance potential Comments
PREHARVEST
azoxystrobin (Abound) Qol2 (strobilurin) contact and systemic single-site (11) high7
azoxystrobin/difenoconazole (Quadris Top) QoI2/DMI3 contact and systemic (local) single-site/
single-site (3/11)
medium premixture
Bordeaux inorganic contact multi-site (M1) low copper and lime based mixture that often includes a zinc adjuvant.
copper inorganic contact multi-site (M1) low fixed coppers (non-copper sulfate materials such as copper hydroxide and copper oxide)
fluopyram/trifloxystrobin
(Luna Sensation)
SDHI4/QoI2 contact and systemic single-site/
single-site (7/11)
medium to high premixture
fluxapyroxad/pyraclostrobin (Priaxor) SDHI4/QoI2 contact and systemic single-site/
single-site (7/11)
medium to high premixture
fosetyl-al (Aliette) phosphonate systemic unknown (P07, 33) low to medium resistant pathogen populations reported
hydrated lime inorganic contact multi-site (M1) low
mefenoxam (Ridomil Gold) phenylamide contact and systemic single-site (4) high7
oxathiapiprolin (Orondis) oxysterol binding proteins contact—fruit/ systemic (local)—roots single-site (49) high
oxytetracycline (Fireline) antibiotic contact protein synthesis (41) high
polyoxin-D (Tavano/Oso) polyoxin contact single-site (19) medium biopesticide
potassium phosphite (Fungi-Phite, Prophyt) phosphonate systemic unknown (multi-site?) (P07, 33) low to medium biopesticide, resistant pathogen populations reported
streptomycin (Firewall) antibiotic systemic protein synthesis (25) high
POSTHARVEST
fludioxonil (Graduate) phenylpyrrole contact single-site (oligo-site) (12) medium
fludioxonil/azoxystrobin (Graduate A+) phenylpyrrole/Qol2 (strobilurin) contact/locally systemic few (multi-site) (11/12) medium premixture
imazalil (FungaFlor 500EC) DMI3 systemic (local) single-site (3) high resistant pathogen populations reported
pyrimethanil (Penbotec) AP5 mostly contact, slightly systemic (on most crops) single-site (9) high7 resistant pathogen populations reported
                                                                                           
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. Fungicides with different group numbers are suitable to alternate in a resistance management program. In California, make no more than one application of a fungicide with a mode-of-action group number associated with high resistance risk before rotating to a fungicide with a different mode-of-action group number; for other fungicides, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action group number.
2 QoI = Quinone outside inhibitor (strobilurin)
3 DMI = Demethylation inhibitors
4 SDHI = Succinate dehydrogenase inhibitors
5 AP = Anilinopyrimidine
6 MBC = methylbenzimidazole carbamate
7 Resistance has been found in California for certain fungicides with a single-site mode of action. To reduce the risk of resistance development, take the mode of action into account when choosing a fungicide. At the beginning of a treatment program, use a fungicide with a multi-site mode of action; for subsequent applications rotate or mix fungicides with different mode of action FRAC numbers. Use labeled rates (preferably the upper range) of the single-site fungicides, and limit the total number of applications per season.

Acknowledgment: Adaskaveg et al., 2022. Fungicides, Bactericides, Biocontrols, and Natural Products for Deciduous Tree Fruit and Nut, Citrus, Strawberry, and Vine Crops in California. (PDF)

Text Updated: 01/19