June Walnut Orchard Management Considerations

Katherine Jarvis-Shean, UCCE Orchard Advisor, Sacramento, Solano and Yolo Counties
Luke Milliron, UCCE Orchard Advisor, Butte, Glenn, & Tehama Counites
Janine Hasey, UCCE Farm Advisor Emerita, Sutter, Yuba, Colusa Counties

Please note that the following are general recommendations intended to help you keep track of regular practices in a busy time; the optimal timing for management practices may vary based on specific location and conditions.

  • Irrigation: Keep an eye on soil moisture and/or stem water potential to avoid overwatering, and potential subsequent harm to root and overall tree health. If using the pressure chamber, waiting to irrigate until trees are 2 to 3 bars drier than the fully watered baseline is a prudent approach. Learn more from our article on Advanced SWP Interpretation in Walnut.
  • Walnut Husk Fly: Hang walnut husk fly traps by June 1. Yellow sticky traps charged with an ammonium carbonate lure work best. Check traps 2 to 3 times per week and treat based on detection of eggs in trapped females, overall trap catch numbers, or the first flies caught depending on spray material used, husk fly population, and previous damage. For more details on treatment decision-making, see our article on Walnut Husk Fly Biology, Monitoring, and Spray Timing.
  • Codling Moth: Keep monitoring codling moth traps, to determine subsequent biofixes. Use trap catches, dropped nut evaluation, canopy counts, and orchard history to determine need to treat second flight. See the UC IPM page on Codling Moth in Walnuts for more information.
  • Spider Mites: Look for spider mites and their predators on the leaflets already being examined for aphids. Examine an additional 5 leaflets from higher branches for a total of 10 leaflets from 10 trees. Yellows sticky cards for sixspotted thrips will also inform presence and activity of this spider mite predator. Monitor weekly through August. Treatment guidelines based on spider mite and predator presence, as well as organophosphate or pyrethroid use can be found on the UC IPM page for Webspinning Spider Mite.
  • Bot Canker: If applying only one fungicide spray for Bot canker, a mid-June to mid-July spray timing significantly reduced blighted shoots compared with a no spray treatment. Prune out dead branches to reduce inoculum now that threat of rain has passed.


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