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UC Pest Management Guidelines

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Walnut

Efficacy of Bactericides and Treatment Timings for Walnut Blight

(Reviewed 3/10, updated 5/10)

In this Guideline:

BACTERICIDE EFFICACY

Material Resistance risk (FRAC#)1 Walnut blight2 Phytotoxicity
Bordeaux2 low (M1) +++ NP
Fixed coppers2 medium (M1) +++ ++3
Copper-maneb** low (M1/M3) ++++ NP
Copper-mancozeb*4 low (M1/M3) ++++ NP
Copper-maneb-surfactant
(single application)**		 low (M1/M3) + NP
Regalia low ++ NP
Serenade low (44) + NP
Zinc-Copper Bordeaux low (M1) +++ NP
Rating: ++++ = excellent and consistent, +++ = good and reliable, ++ = moderate and variable, + = limited and erratic, and NP = not phytotoxic.
* Registration pending in California.
** Not registered, label withdrawn or inactive.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.
2 Copper resistance occurs within sub-populations of Xanthomonas axenopodis pv. juglandis.
3 Phytotoxicity of fixed coppers can be reduced with the addition of lime or agricultural oils to the tank mixture.
4 Currently, in 2010, a Section 18 Emergency registration has been approved for mancozeb under the label Manzate Prostick 75DF or Manzate Flowable.
5 A single application with a surfactant is not recommended because of build up of populations on buds that may increase disease in subsequent years.

TREATMENT TIMINGS

Note: Timings listed are effective but not all may be required for disease control. Timings used
will depend upon orchard history of disease and weather conditions each year.
Disease Catkin emergence Terminal bud break 1 week after bud break 7-10 day intervals1 May2
Walnut blight3 ++ +++ +++ ++1 +
1 A temperature-leaf wetness model (e.g., XanthoCast) is available for determining optimum timing of bactericide applications.
2 Late spring rains are less conducive to disease provided bloom is not delayed by low chilling.
3 Male and female flowers are susceptible beginning with their emergence, depending on wetness and temperatures conducive to disease development.

Adaskaveg, J. E., B. A. Holtz, T. J. Michailides, and W. D. Gubler. 2010. Efficacy and Timing of Fungicides, Bactericides, and Biologicals for Deciduous Tree Fruit, Nut, Strawberry, and Vine Crops (1.1 MB, PDF)

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471
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