Agriculture: Walnut Pest Management Guidelines

General Properties of Fungicides Used in Walnuts

Common name
(Example trade name)
Chemical class1 Mode of action
(FRAC1 group number)
Activity Resistance potential Comments
azoxystrobin/difenoconazole (Quadris Top) QoI2/DMI3-triazole single-site/single-site (11/3) contact, systemic (local) medium  
azoxystrobin/propiconazole (Quilt Xcel) QoI2/DMI3-triazole single-site/single-site (11/3) contact, systemic (local) medium  
copper inorganic multi-site (M1) contact low  
difenoconazole/cyprodinil
(Inspire Super)
DMI3-triazole /AP7 single-site/single-site (3/9) contact, systemic medium  
fluopyram/tebuconazole
(Luna Experience)
SDHI4 single-site/single-site (7/3) contact, systemic medium  
fluopyram/trifloxystrobin
(Luna Sensation)
SDHI4/QoI2 single-site/single-site (7/11) contact, systemic (local) medium to high  
flutriafol (Rhyme) DMI3-triazole single-site (3) systemic (local) high  
mancozeb (Dithane, Manzate) carbamate (EBDC) 5 multi-site (M3) contact low  
mefenoxam (Ridomil Gold) phenylamide single-site (4) contact, systemic high8  
metconazole (Quash) DMI3-triazole single-site (3) systemic (local) high  
penthiopyrad (Fontelis) SDHI4 single-site (7) contact high8  
phosphorous acid (Fosphite) phosphorous acid and salts unknown, multi-site? (P 07, 33) systemic medium  
polyoxin-D (Ph-D) chitin synthesis
inhibitor
single-site (19) contact medium  
pyraclostrobin/boscalid
(Pristine)
Qol2/SDHI4 single-site/single-site (11/7) contact, systemic (local) medium to high  
pyraclostrobin/fluxapyroxad (Merivon) Qol3/SDHI4 single-site/single-site (11/7) contact, systemic medium to high  
tebuconazole (Tebuzol) DMI3-triazole single-site (3) systemic (local) high  
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 or strobilurin
3 DMI = demethylation (sterol) inhibitor
4 SDHI = succinate dehydrogenase inhibitor
5 EBDC = ethylene bisdithiocarbamate
6 MBC = methyl benzimidazole carbamate
7 AP = anilinopyrimidine
8 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: 06/17