Agriculture: Walnut Pest Management Guidelines

Most Effective Treatment Timing for Key Diseases

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 7–10 day intervals Apr. May June July Aug.
(3-wk before hull split)
Sept.
(20–30% hull split)
Oct. Nov.
(1st wk)
Anthracnose1 0 0 0 24 3 2 0 0 0 0 0
Botryosphaeria blight 0 0 0 1 2 3 3 2 0 1 1
Kernel mold2 0 0 0 0 0 0 0 2 2 0 0
Walnut blight3, 4, 5 25 3 3 3 2 1 0 0 0 0 0
Rating: 3 = most effective, 2 = moderately effective, 1 = least effective, and 0 = ineffective
1 Make the first application when the size of the expanding leaves is about half of its final size. This first application stage is critical.
2 Timing for kernel mold is based on a mixture rotation of Merivon (FRAC group 7/11) and Teb (FRAC group 3) followed by Rhyme (FRAC group 3) at the timings indicated. This mixture rotation is ‘3' based on the ratings in the efficacy table above.
3 A temperature-leaf wetness model (e.g., Xanthocast) is available for determining optimum timing of bactericide applications.
4 Late spring rains are less conducive to disease, provided bloom is not delayed by low chilling.
5 Male and female flowers are susceptible beginning with their emergence, depending on wetness and temperatures conducive to disease development.

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: 03/22